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Maxim Svistunov Marie Doleželová Stephen Wadeley Tomáš Čapek Jaromír Hradílek Douglas Silas Jana Heves Petr Kovář Peter Ondrejka Petr Bokoč Martin Prpič Eliška Slobodová Eva Kopalová Miroslav Svoboda David OBrien Michael Hideo Don Domingo John Ha Red Hat Enterprise Linux 7 System Administrators Guide Deployment Configuration and Administration of Red Hat Enterprise Linux 7

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Red Hat Enterprise Linux 7 System Administrators Guide Deployment Configuration and Administration of Red Hat Enterprise Linux 7 Maxim Svistunov Red Hat Customer Content Services msvistunredhat.com Marie Doleželová Red Hat Customer Content Services mdolezelredhat.com Stephen Wadeley Red Hat Customer Content Services swadeleyredhat.com Tomáš Čapek Red Hat Customer Content Services tcapekredhat.com Jaromír Hradílek Red Hat Customer Content Services Douglas Silas Red Hat Customer Content Services Jana Heves Red Hat Customer Content Services Petr Kovář Red Hat Customer Content Services Peter Ondrejka Red Hat Customer Content Services Petr Bokoč Red Hat Customer Content Services Martin Prpič Red Hat Product Security Eliška Slobodová Red Hat Customer Content Services Eva Kopalová Red Hat Customer Content Services Miroslav Svoboda Red Hat Customer Content Services David OBrien Red Hat Customer Content Services

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Michael Hideo Red Hat Customer Content Services Don Domingo Red Hat Customer Content Services John Ha Red Hat Customer Content Services

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Legal Notice Copyright © 2016 Red Hat Inc. This document is licensed by Red Hat under the Creative Commons Attribution-ShareAlike 3.0 Unported License. If you distribute this document or a modified version of it you must provide attribution to Red Hat Inc. and provide a link to the original. If the document is modified all Red Hat trademarks must be removed. Red Hat as the licensor of this document waives the right to enforce and agrees not to assert Section 4d of CC-BY-SA to the fullest extent permitted by applicable law. Red Hat Red Hat Enterprise Linux the Shadowman logo JBoss OpenShift Fedora the Infinity logo and RHCE are trademarks of Red Hat Inc. registered in the United States and other countries. Linux ® is the registered trademark of Linus Torvalds in the United States and other countries. Java ® is a registered trademark of Oracle and/or its affiliates. XFS ® is a trademark of Silicon Graphics International Corp. or its subsidiaries in the United States and/or other countries. MySQL ® is a registered trademark of MySQL AB in the United States the European Union and other countries. Node.js ® is an official trademark of Joyent. Red Hat Software Collections is not formally related to or endorsed by the official Joyent Node.js open source or commercial project. The OpenStack ® Word Mark and OpenStack logo are either registered trademarks/service marks or trademarks/service marks of the OpenStack Foundation in the United States and other countries and are used with the OpenStack Foundations permission. We are not affiliated with endorsed or sponsored by the OpenStack Foundation or the OpenStack community. All other trademarks are the property of their respective owners. Abstract The System Administrators Guide documents relevant information regarding the deployment configuration and administration of Red Hat Enterprise Linux 7. It is oriented towards system administrators with a basic understanding of the system. To expand your expertise you might also be interested in the Red Hat System Administration I RH124 Red Hat System Administration II RH134 Red Hat System Administration III RH254 or RHCSA Rapid Track RH199 training courses.

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Table of Contents ⁠Part I. Basic Syst em Configurat ion ⁠Chapt er 1 . Syst em Locale and Keyboard Configurat ion ⁠1.1. Setting the System Lo cale ⁠1.2. Chang ing the Keyb o ard Layo ut ⁠1.3. Ad d itio nal Reso urces ⁠Chapt er 2 . Configuring t he Dat e and T ime ⁠2.1. Using the timed atectl Co mmand ⁠2.2. Using the d ate Co mmand ⁠2.3. Using the hwclo ck Co mmand ⁠2.4. Ad d itio nal Reso urces ⁠Chapt er 3. Managing Users and Groups ⁠3.1. Intro d uctio n to Users and Gro up s ⁠3.2. Manag ing Users in a Grap hical Enviro nment ⁠3.3. Using Co mmand -Line To o ls ⁠3.4. Ad d itio nal Reso urces ⁠Chapt er 4 . Access Cont rol List s ⁠4.1. Mo unting File Systems ⁠4.2. Setting Access ACLs ⁠4.3. Setting Default ACLs ⁠4.4. Retrieving ACLs ⁠4.5. Archiving File Systems With ACLs ⁠4.6 . Co mp atib ility with Old er Systems ⁠4.7. ACL References ⁠Chapt er 5. Gaining Privileges ⁠5.1. The su Co mmand ⁠5.2. The sud o Co mmand ⁠5.3. Ad d itio nal Reso urces ⁠Part II. Subscript ion and Support ⁠Chapt er 6 . Regist ering t he Syst em and Managing Subscript ions ⁠6 .1. Reg istering the System and Attaching Sub scrip tio ns ⁠6 .2. Manag ing So ftware Rep o sito ries ⁠6 .3. Remo ving Sub scrip tio ns ⁠6 .4. Ad d itio nal Reso urces ⁠Chapt er 7 . Accessing Support Using t he Red Hat Support T ool ⁠7.1. Installing the Red Hat Sup p o rt To o l ⁠7.2. Reg istering the Red Hat Sup p o rt To o l Using the Co mmand Line ⁠7.3. Using the Red Hat Sup p o rt To o l in Interactive Shell Mo d e ⁠7.4. Co nfig uring the Red Hat Sup p o rt To o l ⁠7.5. Op ening and Up d ating Sup p o rt Cases Using Interactive Mo d e ⁠7.6 . Viewing Sup p o rt Cases o n the Co mmand Line ⁠7.7. Ad d itio nal Reso urces ⁠Part III. Inst alling and Managing Soft ware ⁠Chapt er 8 . Yum ⁠8 .1. Checking Fo r and Up d ating Packag es ⁠8 .2. Wo rking with Packag es 6 7 7 9 10 1 2 12 15 17 19 2 1 21 22 24 32 34 34 34 36 36 36 37 37 39 39 40 41 4 3 4 4 44 45 45 46 4 7 47 47 47 47 49 51 51 52 53 53 59 T able of Cont ent s 1

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. . . . . . . . . . . . . . . . . . . . ⁠8 .2. Wo rking with Packag es ⁠8 .3. Wo rking with Packag e Gro up s ⁠8 .4. Wo rking with Transactio n Histo ry ⁠8 .5. Co nfig uring Yum and Yum Rep o sito ries ⁠8 .6 . Yum Plug -ins ⁠8 .7. Ad d itio nal Reso urces ⁠Part IV. Infrast ruct ure Services ⁠Chapt er 9 . Managing Services wit h syst emd ⁠9 .1. Intro d uctio n to systemd ⁠9 .2. Manag ing System Services ⁠9 .3. Wo rking with systemd Targ ets ⁠9 .4. Shutting Do wn Susp end ing and Hib ernating the System ⁠9 .5. Co ntro lling systemd o n a Remo te Machine ⁠9 .6 . Creating and Mo d ifying systemd Unit Files ⁠9 .7. Ad d itio nal Reso urces ⁠Chapt er 1 0 . OpenSSH ⁠10 .1. The SSH Pro to co l ⁠10 .2. Co nfig uring Op enSSH ⁠10 .3. Op enSSH Clients ⁠10 .4. Mo re Than a Secure Shell ⁠10 .5. Ad d itio nal Reso urces ⁠Chapt er 1 1 . T igerVNC ⁠11.1. VNC Server ⁠11.2. Sharing an Existing Deskto p ⁠11.3. VNC Viewer ⁠11.4. Ad d itio nal Reso urces ⁠Part V. Servers ⁠Chapt er 1 2 . Web Servers ⁠12.1. The Ap ache HTTP Server ⁠Chapt er 1 3. Mail Servers ⁠13.1. Email Pro to co ls ⁠13.2. Email Pro g ram Classificatio ns ⁠13.3. Mail Transp o rt Ag ents ⁠13.4. Mail Delivery Ag ents ⁠13.5. Mail User Ag ents ⁠13.6 . Ad d itio nal Reso urces ⁠Chapt er 1 4 . File and Print Servers ⁠14.1. Samb a ⁠14.2. FTP ⁠14.3. Print Setting s ⁠Chapt er 1 5. Configuring NT P Using t he chrony Suit e ⁠15.1. Intro d uctio n to the chro ny Suite ⁠15.2. Und erstand ing chro ny and Its Co nfig uratio n ⁠15.3. Using chro ny ⁠15.4. Setting Up chro ny fo r Different Enviro nments ⁠15.5. Using chro nyc ⁠15.6 . Ad d itio nal Reso urces 59 6 8 71 78 8 9 9 3 9 4 9 5 9 5 9 7 10 5 10 9 111 112 127 1 30 130 133 141 144 145 1 4 7 147 151 152 155 1 56 1 57 157 1 8 2 18 2 18 5 18 6 19 8 20 5 20 6 2 0 9 20 9 223 229 2 4 9 249 250 256 26 1 26 2 26 3 Syst em Administ rat ors Guide 2

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Configuring NT P Using nt pd ⁠16 .1. Intro d uctio n to NTP ⁠16 .2. NTP Strata ⁠16 .3. Und erstand ing NTP ⁠16 .4. Und erstand ing the Drift File ⁠16 .5. UTC Timezo nes and DST ⁠16 .6 . Authenticatio n Op tio ns fo r NTP ⁠16 .7. Manag ing the Time o n Virtual Machines ⁠16 .8 . Und erstand ing Leap Seco nd s ⁠16 .9 . Und erstand ing the ntp d Co nfig uratio n File ⁠16 .10 . Und erstand ing the ntp d Sysco nfig File ⁠16 .11. Disab ling chro ny ⁠16 .12. Checking if the NTP Daemo n is Installed ⁠16 .13. Installing the NTP Daemo n ntp d ⁠16 .14. Checking the Status o f NTP ⁠16 .15. Co nfig ure the Firewall to Allo w Inco ming NTP Packets ⁠16 .16 . Co nfig ure ntp d ate Servers ⁠16 .17. Co nfig ure NTP ⁠16 .18 . Co nfig uring the Hard ware Clo ck Up d ate ⁠16 .19 . Co nfig uring Clo ck So urces ⁠16 .20 . Ad d itio nal Reso urces ⁠Chapt er 1 7 . Configuring PT P Using pt p4 l ⁠17.1. Intro d uctio n to PTP ⁠17.2. Using PTP ⁠17.3. Using PTP with Multip le Interfaces ⁠17.4. Sp ecifying a Co nfig uratio n File ⁠17.5. Using the PTP Manag ement Client ⁠17.6 . Synchro nizing the Clo cks ⁠17.7. Verifying Time Synchro nizatio n ⁠17.8 . Serving PTP Time with NTP ⁠17.9 . Serving NTP Time with PTP ⁠17.10 . Synchro nize to PTP o r NTP Time Using timemaster ⁠17.11. Imp ro ving Accuracy ⁠17.12. Ad d itio nal Reso urces ⁠Part VI. Monit oring and Aut omat ion ⁠Chapt er 1 8 . Syst em Monit oring T ools ⁠18 .1. Viewing System Pro cesses ⁠18 .2. Viewing Memo ry Usag e ⁠18 .3. Viewing CPU Usag e ⁠18 .4. Viewing Blo ck Devices and File Systems ⁠18 .5. Viewing Hard ware Info rmatio n ⁠18 .6 . Checking fo r Hard ware Erro rs ⁠18 .7. Mo nito ring Perfo rmance with Net-SNMP ⁠18 .8 . Ad d itio nal Reso urces ⁠Chapt er 1 9 . OpenLMI ⁠19 .1. Ab o ut Op enLMI ⁠19 .2. Installing Op enLMI ⁠19 .3. Co nfig uring SSL Certificates fo r Op enPeg asus ⁠19 .4. Using LMIShell ⁠19 .5. Using Op enLMI Scrip ts ⁠19 .6 . Ad d itio nal Reso urces 2 6 5 26 5 26 5 26 6 26 7 26 7 26 7 26 8 26 8 26 8 270 270 271 271 271 271 272 273 278 279 28 0 2 8 2 28 2 28 4 28 7 28 7 28 7 28 8 28 9 29 1 29 2 29 2 29 6 29 6 2 9 8 2 9 9 29 9 30 2 30 4 30 4 310 312 314 327 32 9 329 330 331 336 374 374 T able of Cont ent s 3

slide 9:

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Ad d itio nal Reso urces ⁠Chapt er 2 0 . Viewing and Managing Log Files ⁠20 .1. Lo cating Lo g Files ⁠20 .2. Basic Co nfig uratio n o f Rsyslo g ⁠20 .3. Using the New Co nfig uratio n Fo rmat ⁠20 .4. Wo rking with Queues in Rsyslo g ⁠20 .5. Co nfig uring rsyslo g o n a Lo g g ing Server ⁠20 .6 . Using Rsyslo g Mo d ules ⁠20 .7. Interactio n o f Rsyslo g and Jo urnal ⁠20 .8 . Structured Lo g g ing with Rsyslo g ⁠20 .9 . Deb ug g ing Rsyslo g ⁠20 .10 . Using the Jo urnal ⁠20 .11. Manag ing Lo g Files in a Grap hical Enviro nment ⁠20 .12. Ad d itio nal Reso urces ⁠Chapt er 2 1 . Aut omat ing Syst em T asks ⁠21.1. Cro n and Anacro n ⁠21.2. At and Batch ⁠21.3. Sched uling a Jo b to Run o n Next Bo o t Using a systemd Unit File ⁠21.4. Ad d itio nal Reso urces ⁠Chapt er 2 2 . Aut omat ic Bug Report ing T ool ABRT ⁠22.1. Intro d uctio n to ABRT ⁠22.2. Installing ABRT and Starting its Services ⁠22.3. Co nfig uring ABRT ⁠22.4. Detecting So ftware Pro b lems ⁠22.5. Hand ling Detected Pro b lems ⁠22.6 . Ad d itio nal Reso urces ⁠Chapt er 2 3. OProfile ⁠23.1. Overview o f To o ls ⁠23.2. Using o p erf ⁠23.3. Co nfig uring OPro file Using Leg acy Mo d e ⁠23.4. Starting and Sto p p ing OPro file Using Leg acy Mo d e ⁠23.5. Saving Data in Leg acy Mo d e ⁠23.6 . Analyzing the Data ⁠23.7. Und erstand ing the /d ev/o p ro file/ d irecto ry ⁠23.8 . Examp le Usag e ⁠23.9 . OPro file Sup p o rt fo r Java ⁠23.10 . Grap hical Interface ⁠23.11. OPro file and SystemTap ⁠23.12. Ad d itio nal Reso urces ⁠Part VII. Kernel Module and Driver Configurat ion ⁠Chapt er 2 4 . Working wit h t he GRUB 2 Boot Loader ⁠24.1. Intro d uctio n to GRUB 2 ⁠24.2. Co nfig uring the GRUB 2 Bo o t Lo ad er ⁠24.3. Making Temp o rary Chang es to a GRUB 2 Menu ⁠24.4. Making Persistent Chang es to a GRUB 2 Menu Using the g rub b y To o l ⁠24.5. Custo mizing the GRUB 2 Co nfig uratio n File ⁠24.6 . Pro tecting GRUB 2 with a Passwo rd ⁠24.7. Reinstalling GRUB 2 ⁠24.8 . GRUB 2 o ver a Serial Co nso le 374 37 6 376 376 39 0 39 2 40 1 40 5 411 412 415 415 421 426 4 2 8 428 433 437 438 4 4 0 440 440 442 449 451 453 4 55 455 456 459 46 4 46 5 46 5 470 471 471 472 475 475 4 7 7 4 7 8 478 479 479 48 0 48 2 48 7 48 8 48 9 Syst em Administ rat ors Guide 4

slide 10:

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Terminal Menu Ed iting During Bo o t ⁠24.10 . Unified Extensib le Firmware Interface UEFI Secure Bo o t ⁠24.11. Ad d itio nal Reso urces ⁠Chapt er 2 5. Manually Upgrading t he Kernel ⁠25.1. Overview o f Kernel Packag es ⁠25.2. Prep aring to Up g rad e ⁠25.3. Do wnlo ad ing the Up g rad ed Kernel ⁠25.4. Perfo rming the Up g rad e ⁠25.5. Verifying the Initial RAM Disk Imag e ⁠25.6 . Verifying the Bo o t Lo ad er ⁠Chapt er 2 6 . Working wit h Kernel Modules ⁠26 .1. Listing Currently-Lo ad ed Mo d ules ⁠26 .2. Disp laying Info rmatio n Ab o ut a Mo d ule ⁠26 .3. Lo ad ing a Mo d ule ⁠26 .4. Unlo ad ing a Mo d ule ⁠26 .5. Setting Mo d ule Parameters ⁠26 .6 . Persistent Mo d ule Lo ad ing ⁠26 .7. Installing Mo d ules fro m a Driver Up d ate Disk ⁠26 .8 . Sig ning Kernel Mo d ules fo r Secure Bo o t ⁠26 .9 . Ad d itio nal Reso urces ⁠Part VIII. Syst em Backup and Recovery ⁠Chapt er 2 7 . Relax- and- Recover ReaR ⁠27.1. Basic ReaR Usag e ⁠27.2. Integ rating ReaR with Backup So ftware ⁠Appendix A. RPM ⁠A.1. RPM Desig n Go als ⁠A.2. Using RPM ⁠A.3. Find ing and Verifying RPM Packag es ⁠A.4. Co mmo n Examp les o f RPM Usag e ⁠A.5. Ad d itio nal Reso urces ⁠Appendix B. Revision Hist ory ⁠B.1. Ackno wled g ments ⁠Index 49 1 49 6 49 7 4 9 9 49 9 50 0 50 1 50 2 50 2 50 5 50 7 50 7 50 8 511 512 513 514 514 517 523 52 5 52 6 526 532 536 536 537 543 544 545 54 6 546 54 6 T able of Cont ent s 5

slide 11:

⁠Part I. Basic System Configuration This part covers basic system administration tasks such as keyboard configuration date and time configuration managing users and groups and gaining privileges. Syst em Administ rat ors Guide 6

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Chapter 1. System Locale and Keyboard Configuration The system locale specifies the language settings of system services and user interfaces. The keyboard layout settings control the layout used on the text console and graphical user interfaces. These settings can be made by modifying the /etc/locale.conf configuration file or by using the localectl utility. Also you can use the graphical user interface to perform the task for a description of this method see Red Hat Enterprise Linux 7 Installation Guide. 1.1. Setting the System Locale System-wide locale settings are stored in the /etc/locale.conf file which is read at early boot by the systemd daemon. The locale settings configured in /etc/locale.conf are inherited by every service or user unless individual programs or individual users override them. The basic file format of /etc/locale.conf is a newline-separated list of variable assignments. For example German locale with English messages in /etc/locale.conf looks as follows: LANGde_DE.UTF-8 LC_MESSAGESC Here the LC_MESSAGES option determines the locale used for diagnostic messages written to the standard error output. To further specify locale settings in /etc/locale.conf you can use several other options the most relevant are summarized in Table 1.1 “Options configurable in /etc/locale.conf”. See the locale7 manual page for detailed information on these options. Note that the LC_ALL option which represents all possible options should not be configured in /etc/locale.conf. Table 1.1. Options configurable in /etc/locale.conf Option Description LANG Provides a default value for the system locale. LC_COLLATE Changes the behavior of functions which compare strings in the local alphabet. LC_CTYPE Changes the behavior of the character handling and classification functions and the multibyte character functions. LC_NUMERIC Describes the way numbers are usually printed with details such as decimal point versus decimal comma. LC_TIME Changes the display of the current time 24-hour versus 12-hour clock. LC_MESSAGES Determines the locale used for diagnostic messages written to the standard error output. 1.1.1. Displaying the Current Status The localectl command can be used to query and change the system locale and keyboard layout settings. To show the current settings use the status option: localectl status ⁠Chapt er 1 . Syst em Locale and Keyboard Configurat ion 7

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Example 1.1. Displaying the Current Status The output of the previous command lists the currently set locale keyboard layout configured for the console and for the X11 window system. localectl status System Locale: LANGen_US.UTF-8 VC Keymap: us X11 Layout: n/a 1.1.2. Listing Available Locales To list all locales available for your system type: localectl list-locales Example 1.2. Listing Locales Imagine you want to select a specific English locale but you are not sure if it is available on the system. You can check that by listing all English locales with the following command: localectl list-locales | grep en_ en_AG en_AG.utf8 en_AU en_AU.iso88591 en_AU.utf8 en_BW en_BW.iso88591 en_BW.utf8 output truncated 1.1.3. Setting the Locale To set the default system locale use the following command as root: localectl set-locale LANGlocale Replace locale with the locale name found with the localectl list-locales command. The above syntax can also be used to configure parameters from Table 1.1 “Options configurable in /etc/locale.conf”. Example 1.3. Changing the Default Locale For example if you want to set British English as your default locale first find the name of this locale by using list-locales. Then as root type the command in the following form: localectl set-locale LANGen_GB.utf8 Syst em Administ rat ors Guide 8

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1.2. Changing the Keyboard Layout The keyboard layout settings enable the user to control the layout used on the text console and graphical user interfaces. 1.2.1. Displaying the Current Settings As mentioned before you can check your current keyboard layout configuration with the following command: localectl status Example 1.4 . Displaying the Keyboard Settings In the following output you can see the keyboard layout configured for the virtual console and for the X11 window system. localectl status System Locale: LANGen_US.utf8 VC Keymap: us X11 Layout: us 1.2.2. Listing Available Keymaps To list all available keyboard layouts that can be configured on your system type: localectl list-keymaps Example 1.5. Searching for a Particular Keymap You can use grep to search the output of the previous command for a specific keymap name. There are often multiple keymaps compatible with your currently set locale. For example to find available Czech keyboard layouts type: localectl list-keymaps | grep cz cz cz-cp1250 cz-lat2 cz-lat2-prog cz-qwerty cz-us-qwertz sunt5-cz-us sunt5-us-cz 1.2.3. Setting the Keymap ⁠Chapt er 1 . Syst em Locale and Keyboard Configurat ion 9

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To set the default keyboard layout for your system use the following command as root: localectl set-keymap map Replace map with the name of the keymap taken from the output of the localectl list-keymaps command. Unless the --no-convert option is passed the selected setting is also applied to the default keyboard mapping of the X11 window system after converting it to the closest matching X11 keyboard mapping. This also applies in reverse you can specify both keymaps with the following command as root: localectl set-x11-keymap map If you want your X11 layout to differ from the console layout use the --no-convert option. localectl --no-convert set-x11-keymap map With this option the X11 keymap is specified without changing the previous console layout setting. Example 1.6 . Setting the X11 Keymap Separately Imagine you want to use German keyboard layout in the graphical interface but for console operations you want to retain the US keymap. To do so type as root: localectl --no-convert set-x11-keymap de Then you can verify if your setting was successful by checking the current status: localectl status System Locale: LANGde_DE.UTF-8 VC Keymap: us X11 Layout: de Apart from keyboard layout map three other options can be specified: localectl set-x11-keymap map model variant options Replace model with the keyboard model name variant and options with keyboard variant and option components which can be used to enhance the keyboard behavior. These options are not set by default. For more information on X11 Model X11 Variant and X11 Options see the kbd4 man page. 1.3. Additional Resources For more information on how to configure the keyboard layout on Red Hat Enterprise Linux see the resources listed below: Installed Documentation localectl1 — The manual page for the localectl command line utility documents how to use this tool to configure the system locale and keyboard layout. Syst em Administ rat ors Guide 10

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loadkeys1 — The manual page for the loadkeys command provides more information on how to use this tool to change the keyboard layout in a virtual console. See Also Chapter 5 Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands. Chapter 9 Managing Services with systemd provides more information on systemd and documents how to use the systemctl command to manage system services. ⁠Chapt er 1 . Syst em Locale and Keyboard Configurat ion 11

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Chapter 2. Configuring the Date and Time Modern operating systems distinguish between the following two types of clocks: A real-time clock RTC commonly referred to as a hardware clock typically an integrated circuit on the system board that is completely independent of the current state of the operating system and runs even when the computer is shut down. A system clock also known as a software clock that is maintained by the kernel and its initial value is based on the real-time clock. Once the system is booted and the system clock is initialized the system clock is completely independent of the real-time clock. The system time is always kept in Coordinated Universal Time UTC and converted in applications to local time as needed. Local time is the actual time in your current time zone taking into account daylight saving time DST. The real-time clock can use either UTC or local time. UTC is recommended. Red Hat Enterprise Linux 7 offers three command line tools that can be used to configure and display information about the system date and time: the timedatectl utility which is new in Red Hat Enterprise Linux 7 and is part of systemd the traditional date command and the hwclock utility for accessing the hardware clock. 2.1. Using the timedatectl Command The timedatectl utility is distributed as part of the systemd system and service manager and allows you to review and change the configuration of the system clock. You can use this tool to change the current date and time set the time zone or enable automatic synchronization of the system clock with a remote server. For information on how to display the current date and time in a custom format see also Section 2.2 “Using the date Command”. 2.1.1. Displaying the Current Date and T ime To display the current date and time along with detailed information about the configuration of the system and hardware clock run the timedatectl command with no additional command line options: timedatectl This displays the local and universal time the currently used time zone the status of the Network Time Protocol NTP configuration and additional information related to DST. Example 2.1. Displaying the Current Date and Time The following is an example output of the timedatectl command on a system that does not use NTP to synchronize the system clock with a remote server: timedatectl Local time: Mon 2013-09-16 19:30:24 CEST Universal time: Mon 2013-09-16 17:30:24 UTC Timezone: Europe/Prague CEST +0200 NTP enabled: no NTP synchronized: no RTC in local TZ: no Syst em Administ rat ors Guide 12

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DST active: yes Last DST change: DST began at Sun 2013-03-31 01:59:59 CET Sun 2013-03-31 03:00:00 CEST Next DST change: DST ends the clock jumps one hour backwards at Sun 2013-10-27 02:59:59 CEST Sun 2013-10-27 02:00:00 CET Important Changes to the status of chrony or ntpd will not be immediately noticed by timedatectl. If changes to the configuration or status of these tools is made enter the following command: systemctl restart systemd-timedated.services 2.1.2. Changing the Current T ime To change the current time type the following at a shell prompt as root: timedatectl set-time HH:MM:SS Replace HH with an hour MM with a minute and SS with a second all typed in two-digit form. This command updates both the system time and the hardware clock. The result it is similar to using both the date --set and hwclock --systohc commands. The command will fail if an NTP service is enabled. See Section 2.1.5 “Synchronizing the System Clock with a Remote Server” to temporally disable the service. Example 2.2. Changing the Current Time To change the current time to 11:26 p.m. run the following command as root: timedatectl set-time 23:26:00 By default the system is configured to use UTC. To configure your system to maintain the clock in the local time run the timedatectl command with the set-local-rtc option as root: timedatectl set-local-rtc boolean To configure your system to maintain the clock in the local time replace boolean with yes or alternatively y true t or 1. To configure the system to use UTC replace boolean with no or alternatively n false f or 0. The default option is no. 2.1.3. Changing the Current Date To change the current date type the following at a shell prompt as root: ⁠Chapt er 2 . Configuring t he Dat e and T ime 13

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timedatectl set-time YYYY-MM-DD Replace YYYY with a four-digit year MM with a two-digit month and DD with a two-digit day of the month. Note that changing the date without specifying the current time results in setting the time to 00:00:00. Example 2.3. Changing the Current Date To change the current date to 2 June 2013 and keep the current time 11:26 p.m. run the following command as root: timedatectl set-time 2013-06-02 23:26:00 2.1.4 . Changing the T ime Zone To list all available time zones type the following at a shell prompt: timedatectl list-timezones To change the currently used time zone type as root: timedatectl set-timezone time_zone Replace time_zone with any of the values listed by the timedatectl list-timezones command. Example 2.4 . Changing the Time Zone To identify which time zone is closest to your present location use the timedatectl command with the list-timezones command line option. For example to list all available time zones in Europe type: timedatectl list-timezones | grep Europe Europe/Amsterdam Europe/Andorra Europe/Athens Europe/Belgrade Europe/Berlin Europe/Bratislava … To change the time zone to Europe/Prague type as root: timedatectl set-timezone Europe/Prague 2.1.5. Synchronizing the System Clock with a Remote Server Syst em Administ rat ors Guide 14

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As opposed to the manual adjustments described in the previous sections the timedatectl command also allows you to enable automatic synchronization of your system clock with a group of remote servers using the NTP protocol. Enabling NTP enables the chronyd or ntpd service depending on which of them is installed. The NTP service can be enabled and disabled using a command as follows: timedatectl set-ntp boolean To enable your system to synchronize the system clock with a remote NTP server replace boolean with yes the default option. To disable this feature replace boolean with no. Example 2.5. Synchroniz ing the System Clock with a Remote Server To enable automatic synchronization of the system clock with a remote server type: timedatectl set-ntp yes The command will fail if an NTP service is not installed. See Section 15.3.1 “Installing chrony” for more information. 2.2. Using the date Command The date utility is available on all Linux systems and allows you to display and configure the current date and time. It is frequently used in scripts to display detailed information about the system clock in a custom format. For information on how to change the time zone or enable automatic synchronization of the system clock with a remote server see Section 2.1 “Using the timedatectl Command”. 2.2.1. Displaying the Current Date and T ime To display the current date and time run the date command with no additional command line options: date This displays the day of the week followed by the current date local time abbreviated time zone and year. By default the date command displays the local time. To display the time in UTC run the command with the --utc or -u command line option: date --utc You can also customize the format of the displayed information by providing the +"format" option on the command line: date +"format" ⁠Chapt er 2 . Configuring t he Dat e and T ime 15

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Replace format with one or more supported control sequences as illustrated in Example 2.6 “Displaying the Current Date and Time”. See Table 2.1 “Commonly Used Control Sequences” for a list of the most frequently used formatting options or the date1 manual page for a complete list of these options. Table 2.1. Commonly Used Control Sequences Control Sequence Description H The hour in the HH format for example 17. M The minute in the MM format for example 30. S The second in the SS format for example 24. d The day of the month in the DD format for example 16. m The month in the MM format for example 09. Y The year in the YYYY format for example 2013. Z The time zone abbreviation for example CEST. F The full date in the YYYY-MM-DD format for example 2013-09-16. This option is equal to Y-m-d. T The full time in the HH:MM:SS format for example 17:30:24. This option is equal to H:M:S Example 2.6 . Displaying the Current Date and Time To display the current date and local time type the following at a shell prompt: date Mon Sep 16 17:30:24 CEST 2013 To display the current date and time in UTC type the following at a shell prompt: date --utc Mon Sep 16 15:30:34 UTC 2013 To customize the output of the date command type: date +"Y-m-d H:M" 2013-09-16 17:30 2.2.2. Changing the Current T ime To change the current time run the date command with the --set or -s option as root: date --set HH:MM:SS Replace HH with an hour MM with a minute and SS with a second all typed in two-digit form. By default the date command sets the system clock to the local time. To set the system clock in UTC run the command with the --utc or -u command line option: date --set HH:MM:SS --utc Syst em Administ rat ors Guide 16

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Example 2.7. Changing the Current Time To change the current time to 11:26 p.m. run the following command as root: date --set 23:26:00 2.2.3. Changing the Current Date To change the current date run the date command with the --set or -s option as root: date --set YYYY-MM-DD Replace YYYY with a four-digit year MM with a two-digit month and DD with a two-digit day of the month. Note that changing the date without specifying the current time results in setting the time to 00:00:00. Example 2.8. Changing the Current Date To change the current date to 2 June 2013 and keep the current time 11:26 p.m. run the following command as root: date --set 2013-06-02 23:26:00 2.3. Using the hwclock Command hwclock is a utility for accessing the hardware clock also referred to as the Real Time Clock RTC. The hardware clock is independent of the operating system you use and works even when the machine is shut down. This utility is used for displaying the time from the hardware clock. hwclock also contains facilities for compensating for systematic drift in the hardware clock. The hardware clock stores the values of: year month day hour minute and second. It is not able to store the time standard local time or Coordinated Universal Time UTC nor set the Daylight Saving Time DST. The hwclock utility saves its settings in the /etc/adjtime file which is created with the first change you make for example when you set the time manually or synchronize the hardware clock with the system time. Note In Red Hat Enterprise Linux 6 the hwclock command was run automatically on every system shutdown or reboot but it is not in Red Hat Enterprise Linux 7. When the system clock is synchronized by the Network Time Protocol NTP or Precision Time Protocol PTP the kernel automatically synchronizes the hardware clock to the system clock every 11 minutes. ⁠Chapt er 2 . Configuring t he Dat e and T ime 17

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For details about NTP see Chapter 15 Configuring NTP Using the chrony Suite and Chapter 16 Configuring NTP Using ntpd. For information about PTP see Chapter 17 Configuring PTP Using ptp4l. For information about setting the hardware clock after executing ntpdate see Section 16.18 “Configuring the Hardware Clock Update”. 2.3.1. Displaying the Current Date and T ime Running hwclock with no command line options as the root user returns the date and time in local time to standard output. hwclock Note that using the --utc or --localtime options with the hwclock command does not mean you are displaying the hardware clock time in UTC or local time. These options are used for setting the hardware clock to keep time in either of them. The time is always displayed in local time. Additionally using the hwclock --utc or hwclock --local commands does not change the record in the /etc/adjtime file. This command can be useful when you know that the setting saved in /etc/adjtime is incorrect but you do not want to change the setting. On the other hand you may receive misleading information if you use the command an incorrect way. See the hwclock8 manual page for more details. Example 2.9 . Displaying the Current Date and Time To display the current date and the current local time from the hardware clock run as root: hwclock Tue 15 Apr 2014 04:23:46 PM CEST -0.329272 seconds CEST is a time zone abbreviation and stands for Central European Summer Time. For information on how to change the time zone see Section 2.1.4 “Changing the Time Zone”. 2.3.2. Setting the Date and T ime Besides displaying the date and time you can manually set the hardware clock to a specific time. When you need to change the hardware clock date and time you can do so by appending the --set and --date options along with your specification: hwclock --set --date "dd mmm yyyy HH:MM" Replace dd with a day a two-digit number mmm with a month a three-letter abbreviation yyyy with a year a four-digit number HH with an hour a two-digit number MM with a minute a two-digit number. At the same time you can also set the hardware clock to keep the time in either UTC or local time by adding the --utc or --localtime options respectively. In this case UTC or LOCAL is recorded in the /etc/adjtime file. Example 2.10. Setting the Hardware Clock to a Specific Date and Time Syst em Administ rat ors Guide 18

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If you want to set the date and time to a specific value for example to "21:17 October 21 2014" and keep the hardware clock in UTC run the command as root in the following format: hwclock --set --date "21 Oct 2014 21:17" --utc 2.3.3. Synchronizing the Date and T ime You can synchronize the hardware clock and the current system time in both directions. Either you can set the hardware clock to the current system time by using this command: hwclock --systohc Note that if you use NTP the hardware clock is automatically synchronized to the system clock every 11 minutes and this command is useful only at boot time to get a reasonable initial system time. Or you can set the system time from the hardware clock by using the following command: hwclock --hctosys When you synchronize the hardware clock and the system time you can also specify whether you want to keep the hardware clock in local time or UTC by adding the --utc or --localtime option. Similarly to using --set UTC or LOCAL is recorded in the /etc/adjtime file. The hwclock --systohc --utc command is functionally similar to timedatectl set-local- rtc false and the hwclock --systohc --local command is an alternative to timedatectl set-local-rtc true. Example 2.11. Synchroniz ing the Hardware Clock with System Time To set the hardware clock to the current system time and keep the hardware clock in local time run the following command as root: hwclock --systohc --localtime To avoid problems with time zone and DST switching it is recommended to keep the hardware clock in UTC. The shown Example 2.11 “Synchronizing the Hardware Clock with System Time” is useful for example in case of a multi boot with a Windows system which assumes the hardware clock runs in local time by default and all other systems need to accommodate to it by using local time as well. It may also be needed with a virtual machine if the virtual hardware clock provided by the host is running in local time the guest system needs to be configured to use local time too. 2.4. Additional Resources For more information on how to configure the date and time in Red Hat Enterprise Linux 7 see the resources listed below. Installed Documentation ⁠Chapt er 2 . Configuring t he Dat e and T ime 19

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timedatectl1 — The manual page for the timedatectl command line utility documents how to use this tool to query and change the system clock and its settings. date1 — The manual page for the date command provides a complete list of supported command line options. hwclock8 — The manual page for the hwclock command provides a complete list of supported command line options. See Also Chapter 1 System Locale and Keyboard Configuration documents how to configure the keyboard layout. Chapter 5 Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands. Chapter 9 Managing Services with systemd provides more information on systemd and documents how to use the systemctl command to manage system services. Syst em Administ rat ors Guide 20

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Chapter 3. Managing Users and Groups The control of users and groups is a core element of Red Hat Enterprise Linux system administration. This chapter explains how to add manage and delete users and groups in the graphical user interface and on the command line and covers advanced topics such as creating group directories. 3.1. Introduction to Users and Groups While users can be either people meaning accounts tied to physical users or accounts that exist for specific applications to use groups are logical expressions of organization tying users together for a common purpose. Users within a group share the same permissions to read write or execute files owned by that group. Each user is associated with a unique numerical identification number called a user ID UID. Likewise each group is associated with a group ID GID. A user who creates a file is also the owner and group owner of that file. The file is assigned separate read write and execute permissions for the owner the group and everyone else. The file owner can be changed only by root and access permissions can be changed by both the root user and file owner. Additionally Red Hat Enterprise Linux supports access control lists ACLs for files and directories which allow permissions for specific users outside of the owner to be set. For more information about this feature see Chapter 4 Access Control Lists. Reserved User and Gro up IDs Red Hat Enterprise Linux reserves user and group IDs below 1000 for system users and groups. By default the User Manager does not display the system users. Reserved user and group IDs are documented in the setup package. To view the documentation use this command: cat /usr/share/doc/setup/uidgid The recommended practice is to assign non-reserved IDs starting at 5000 as the reserved range can increase in the future. To make the IDs assigned to new users by default start at 5000 change the UID_MIN and GID_MIN directives in the /etc/login.defs file: file contents truncated UID_MIN 5000 file contents truncated GID_MIN 5000 file contents truncated Note For users created before you changed UID_MIN and GID_MIN directives UIDs will still start at the default 1000. Even with new user and group IDs beginning with 5000 it is recommended not to raise IDs reserved by the system above 1000 to avoid conflict with systems that retain the 1000 limit. 3.1.1. User Private Groups ⁠Chapt er 3. Managing Users and Groups 21

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Red Hat Enterprise Linux uses a user private group UPG scheme which makes UNIX groups easier to manage. A user private group is created whenever a new user is added to the system. It has the same name as the user for which it was created and that user is the only member of the user private group. User private groups make it safe to set default permissions for a newly created file or directory allowing both the user and the group of that user to make modifications to the file or directory. The setting which determines what permissions are applied to a newly created file or directory is called a umask and is configured in the /etc/bashrc file. Traditionally on UNIX-based systems the umask is set to 022 which allows only the user who created the file or directory to make modifications. Under this scheme all other users including members of the creators group are not allowed to make any modifications. However under the UPG scheme this “group protection” is not necessary since every user has their own private group. See Section 3.3.4 “Setting Default Permissions for New Files Using umask” for more information. A list of all groups is stored in the /etc/group configuration file. 3.1.2. Shadow Passwords In environments with multiple users it is very important to use shadow passwords provided by the shadow-utils package to enhance the security of system authentication files. For this reason the installation program enables shadow passwords by default. The following is a list of the advantages shadow passwords have over the traditional way of storing passwords on UNIX-based systems: Shadow passwords improve system security by moving encrypted password hashes from the world-readable /etc/passwd file to /etc/shadow which is readable only by the root user. Shadow passwords store information about password aging. Shadow passwords allow to enforce some of the security policies set in the /etc/login.defs file. Most utilities provided by the shadow-utils package work properly whether or not shadow passwords are enabled. However since password aging information is stored exclusively in the /etc/shadow file some utilities and commands do not work without first enabling shadow passwords: The chage utility for setting password-aging parameters. For details see the Password Security section in the Red Hat Enterprise Linux 7 Security Guide. The gpasswd utility for administrating the /etc/group file. The usermod command with the -e --expiredate or -f --inactive option. The useradd command with the -e --expiredate or -f --inactive option. 3.2. Managing Users in a Graphical Environment The Users utility allows you to view modify add and delete local users in the graphical user interface. 3.2.1. Using the Users Settings T ool Press the Super key to enter the Activities Overview type Users and then press Enter. The Users settings tool appears. The Super key appears in a variety of guises depending on the keyboard and other hardware but often as either the Windows or Command key and typically to the left of the Syst em Administ rat ors Guide 22

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Spacebar. Alternatively you can open the Users utility from the Settings menu after clicking your user name in the top right corner of the screen. To make changes to the user accounts first select the Unlock button and authenticate yourself as indicated by the dialog box that appears. Note that unless you have superuser privileges the application will prompt you to authenticate as root. To add and remove users select the + and - button respectively. To add a user to the administrative group wheel change the Account Type from Standard to Administrator. To edit a users language setting select the language and a drop-down menu appears. Figure 3.1. The Users Settings Tool When a new user is created the account is disabled until a password is set. The Password drop- down menu shown in Figure 3.2 “The Password Menu” contains the options to set a password by the administrator immediately choose a password by the user at the first login or create a guest account with no password required to log in. You can also disable or enable an account from this menu. ⁠Chapt er 3. Managing Users and Groups 23

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Figure 3.2. The Password Menu 3.3. Using Command-Line Tools Apart from the Users settings tool described in Section 3.2 “Managing Users in a Graphical Environment” which is designed for basic managing of users you can use command line tools for managing users and groups that are listed in Table 3.1 “Command line utilities for managing users and groups”. Table 3.1. Command line utilities for managing users and groups Utilities Description id Displays user and group IDs. useradd usermod userdel Standard utilities for adding modifying and deleting user accounts. groupadd groupmod groupdel Standard utilities for adding modifying and deleting groups. gpasswd Utility primarily used for modification of group password in the /etc/gshadow file which is used by the newgrp command. pwck grpck Utilities that can be used for verification of the password group and associated shadow files. pwconv pwunconv Utilities that can be used for the conversion of passwords to shadow passwords or back from shadow passwords to standard passwords. grpconv grpunconv Similar to the previous these utilities can be used for conversion of shadowed information for group accounts. Syst em Administ rat ors Guide 24

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3.3.1. Adding a New User To add a new user to the system type the following at a shell prompt as root: useradd options username …where options are command-line options as described in Table 3.2 “Common useradd command- line options”. By default the useradd command creates a locked user account. To unlock the account run the following command as root to assign a password: passwd username Optionally you can set a password aging policy. See the Password Security section in the Red Hat Enterprise Linux 7 Security Guide. Table 3.2. Common useradd command-line options Option Description -c comment comment can be replaced with any string. This option is generally used to specify the full name of a user. -d home_directory Home directory to be used instead of default /home/username/. -e date Date for the account to be disabled in the format YYYY-MM-DD. -f days Number of days after the password expires until the account is disabled. If 0 is specified the account is disabled immediately after the password expires. If -1 is specified the account is not disabled after the password expires. -g group_name Group name or group number for the users default primary group. The group must exist prior to being specified here. -G group_list List of additional supplementary other than default group names or group numbers separated by commas of which the user is a member. The groups must exist prior to being specified here. -m Create the home directory if it does not exist. -M Do not create the home directory. -N Do not create a user private group for the user. -p password The password encrypted with crypt. -r Create a system account with a UID less than 1000 and without a home directory. -s Users login shell which defaults to /bin/bash. -u uid User ID for the user which must be unique and greater than 999. The command-line options associated with the usermod command are essentially the same. Note that if you want to add a user to another supplementary group you need to use the -a --append option with the -G option. Otherwise the list of supplementary groups for the user will be overwritten by those specified with the usermod -G command. ⁠Chapt er 3. Managing Users and Groups 25

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Important The default range of IDs for system and normal users has been changed in Red Hat Enterprise Linux 7 from earlier releases. Previously UID 1-499 was used for system users and values above for normal users. The default range for system users is now 1-999. This change might cause problems when migrating to Red Hat Enterprise Linux 7 with existing users having UIDs and GIDs between 500 and 999. The default ranges of UID and GID can be changed in the /etc/login.defs file. Explaining t he Pro cess The following steps illustrate what happens if the command useradd juan is issued on a system that has shadow passwords enabled: 1. A new line for juan is created in /etc/passwd: juan:x:1001:1001::/home/juan:/bin/bash The line has the following characteristics: It begins with the user name juan. There is an x for the password field indicating that the system is using shadow passwords. A UID greater than 999 is created. Under Red Hat Enterprise Linux 7 UIDs below 1000 are reserved for system use and should not be assigned to users. A GID greater than 999 is created. Under Red Hat Enterprise Linux 7 GIDs below 1000 are reserved for system use and should not be assigned to users. The optional GECOS information is left blank. The GECOS field can be used to provide additional information about the user such as their full name or phone number. The home directory for juan is set to /home/juan/. The default shell is set to /bin/bash. 2. A new line for juan is created in /etc/shadow: juan::14798:0:99999:7::: The line has the following characteristics: It begins with the username juan. Two exclamation marks appear in the password field of the /etc/shadow file which locks the account. Note If an encrypted password is passed using the -p flag it is placed in the /etc/shadow file on the new line for the user. Syst em Administ rat ors Guide 26

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The password is set to never expire. 3. A new line for a group named juan is created in /etc/group: juan:x:1001: A group with the same name as a user is called a user private group. For more information on user private groups see Section 3.1.1 “User Private Groups”. The line created in /etc/group has the following characteristics: It begins with the group name juan. An x appears in the password field indicating that the system is using shadow group passwords. The GID matches the one listed for juans primary group in /etc/passwd. 4. A new line for a group named juan is created in /etc/gshadow: juan::: The line has the following characteristics: It begins with the group name juan. An exclamation mark appears in the password field of the /etc/gshadow file which locks the group. All other fields are blank. 5. A directory for user juan is created in the /home directory: ls -ld /home/juan drwx------. 4 juan juan 4096 Mar 3 18:23 /home/juan This directory is owned by user juan and group juan. It has read write and execute privileges only for the user juan. All other permissions are denied. 6. The files within the /etc/skel/ directory which contain default user settings are copied into the new /home/juan/ directory: ls -la /home/juan total 28 drwx------. 4 juan juan 4096 Mar 3 18:23 . drwxr-xr-x. 5 root root 4096 Mar 3 18:23 .. -rw-r--r--. 1 juan juan 18 Jun 22 2010 .bash_logout -rw-r--r--. 1 juan juan 176 Jun 22 2010 .bash_profile -rw-r--r--. 1 juan juan 124 Jun 22 2010 .bashrc drwxr-xr-x. 4 juan juan 4096 Nov 23 15:09 .mozilla At this point a locked account called juan exists on the system. To activate it the administrator must next assign a password to the account using the passwd command and optionally set password aging guidelines see the Password Security section in the Red Hat Enterprise Linux 7 Security Guide for details. 3.3.2. Adding a New Group ⁠Chapt er 3. Managing Users and Groups 27

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3.3.2. Adding a New Group To add a new group to the system type the following at a shell prompt as root: groupadd options group_name …where options are command-line options as described in Table 3.3 “Common groupadd command-line options”. Table 3.3. Common groupadd command-line options Option Description -f --force When used with -g gid and gid already exists groupadd will choose another unique gid for the group. -g gid Group ID for the group which must be unique and greater than 999. -K --key keyvalue Override /etc/login.defs defaults. -o --non-unique Allows creating groups with duplicate GID. -p --password password Use this encrypted password for the new group. -r Create a system group with a GID less than 1000. 3.3.3. Creating Group Directories System administrators usually like to create a group for each major project and assign people to the group when they need to access that projects files. With this traditional scheme file management is difficult when someone creates a file it is associated with the primary group to which they belong. When a single person works on multiple projects it becomes difficult to associate the right files with the right group. However with the UPG scheme groups are automatically assigned to files created within a directory with the setgid bit set. The setgid bit makes managing group projects that share a common directory very simple because any files a user creates within the directory are owned by the group that owns the directory. For example a group of people need to work on files in the /opt/myproject/ directory. Some people are trusted to modify the contents of this directory but not everyone. 1. As root create the /opt/myproject/ directory by typing the following at a shell prompt: mkdir /opt/myproject 2. Add the myproject group to the system: groupadd myproject 3. Associate the contents of the /opt/myproject/ directory with the myproject group: chown root:myproject /opt/myproject 4. Allow users in the group to create files within the directory and set the setgid bit: chmod 2775 /opt/myproject At this point all members of the myproject group can create and edit files in the /opt/myproject/ directory without the administrator having to change file permissions every time users write new files. To verify that the permissions have been set correctly run the following command: Syst em Administ rat ors Guide 28

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ls -ld /opt/myproject drwxrwsr-x. 3 root myproject 4096 Mar 3 18:31 /opt/myproject 5. Add users to the myproject group: usermod -aG myproject username 3.3.4 . Setting Default Permissions for New Files Using umask When a process creates a file the file has certain default permissions for example -rw-rw-r--. These initial permissions are partially defined by the file mode creation mask also called file permission mask or umask. Every process has its own umask for example bash has umask 0022 by default. Process umask can be changed. What umask co nsist s o f A umask consists of bits corresponding to standard file permissions. For example for umask 0137 the digits mean that: 0 no meaning it is always 0 umask does not affect special bits 1 for owner permissions the execute bit is set 3 for group permissions the execute and write bits are set 7 for others permissions the execute write and read bits are set Umasks can be represented in binary octal or symbolic notation. For example the octal representation 0137 equals symbolic representation urw-gr--o---. Symbolic notation specification is the reverse of the octal notation specification: it shows the allowed permissions not the prohibited permissions. Ho w umask wo rks Umask prohibits permissions from being set for a file: When a bit is set in umask it is unset in the file. When a bit is not set in umask it can be set in the file depending on other factors. The following figure shows how umask 0137 affects creating a new file. ⁠Chapt er 3. Managing Users and Groups 29

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Figure 3.3. Applying umask when creating a file Important For security reasons a regular file cannot have execute permissions by default. Therefore even if umask is 0000 which does not prohibit any permissions a new regular file still does not have execute permissions. However directories can be created with execute permissions: johnserver tmp umask 0000 johnserver tmp touch file johnserver tmp mkdir directory johnserver tmp ls -lh . total 0 drwxrwxrwx. 2 john john 40 Nov 2 13:17 directory -rw-rw-rw-. 1 john john 0 Nov 2 13:17 file 3.3.4.1. Managing umask in Shells For popular shells such as bash ksh zsh and tcsh umask is managed using the umask shell builtin. Processes started from shell inherit its umask. Displaying t he current mask To show the current umask in octal notation: umask 0022 Syst em Administ rat ors Guide 30

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To show the current umask in symbolic notation: umask -S urwxgrxorx Set t ing mask in shell using umask To set umask for the current shell session using octal notation run: umask octal_mask Substitute octal_mask with four or less digits from 0 to 7. When three or less digits are provided permissions are set as if the command contained leading zeros. For example umask 7 translates to 0007. Example 3.1. Setting umask Using Octal Notation To prohibit new files from having write and execute permissions for owner and group and from having any permissions for others: umask 0337 Or simply: umask 337 To set umask for the current shell session using symbolic notation: umask -S symbolic_mask Example 3.2. Setting umask Using Symbolic Notation To set umask 0337 using symbolic notation: umask -S urgro Wo rking wit h t he default shell umask Shells usually have a configuration file where their default umask is set. For bash it is /etc/bashrc. To show the default bash umask: grep -i -B 1 umask /etc/bashrc The output shows if umask is set either using the umask command or the UMASK variable. In the following example umask is set to 022 using the umask command: grep -i -B 1 umask /etc/bashrc By default we want umask to get set. This sets it for non-login shell. ⁠Chapt er 3. Managing Users and Groups 31

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-- if UID -gt 199 "`id -gn`" "`id -un`" then umask 002 else umask 022 To change the default umask for bash change the umask command call or the UMASK variable assignment in /etc/bashrc. This example changes the default umask to 0227: if UID -gt 199 "`id -gn`" "`id -un`" then umask 002 else umask 227 Wo rking wit h t he default shell umask o f a specific user By default bash umask of a new user defaults to the one defined in /etc/bashrc. To change bash umask for a particular user add a call to the umask command in HOME/.bashrc file of that user. For example to change bash umask of user john to 0227: johnserver echo umask 227 /home/john/.bashrc Set t ing default permissio ns fo r newly creat ed ho me direct o ries To change permissions with which user home directories are created change the UMASK variable in the /etc/login.defs file: The permission mask is initialized to this value. If not specified the permission mask will be initialized to 022. UMASK 077 3.4. Additional Resources For more information on how to manage users and groups on Red Hat Enterprise Linux see the resources listed below. Installed Documentation For information about various utilities for managing users and groups see the following manual pages: useradd8 — The manual page for the useradd command documents how to use it to create new users. userdel8 — The manual page for the userdel command documents how to use it to delete users. usermod8 — The manual page for the usermod command documents how to use it to modify users. groupadd8 — The manual page for the groupadd command documents how to use it to create new groups. Syst em Administ rat ors Guide 32

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groupdel8 — The manual page for the groupdel command documents how to use it to delete groups. groupmod8 — The manual page for the groupmod command documents how to use it to modify group membership. gpasswd1 — The manual page for the gpasswd command documents how to manage the /etc/group file. grpck8 — The manual page for the grpck command documents how to use it to verify the integrity of the /etc/group file. pwck8 — The manual page for the pwck command documents how to use it to verify the integrity of the /etc/passwd and /etc/shadow files. pwconv8 — The manual page for the pwconv pwunconv grpconv and grpunconv commands documents how to convert shadowed information for passwords and groups. id1 — The manual page for the id command documents how to display user and group IDs. umask2 — The manual page for the umask command documents how to work with the file mode creation mask. For information about related configuration files see: group5 — The manual page for the /etc/group file documents how to use this file to define system groups. passwd5 — The manual page for the /etc/passwd file documents how to use this file to define user information. shadow5 — The manual page for the /etc/shadow file documents how to use this file to set passwords and account expiration information for the system. Online Documentation Red Hat Enterprise Linux 7 Security Guide — The Security Guide for Red Hat Enterprise Linux 7 provides additional information how to ensure password security and secure the workstation by enabling password aging and user account locking. See Also Chapter 5 Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands. ⁠Chapt er 3. Managing Users and Groups 33

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Chapter 4. Access Control Lists Files and directories have permission sets for the owner of the file the group associated with the file and all other users for the system. However these permission sets have limitations. For example different permissions cannot be configured for different users. Thus Access Control Lists ACLs were implemented. The Red Hat Enterprise Linux kernel provides ACL support for the ext3 file system and NFS-exported file systems. ACLs are also recognized on ext3 file systems accessed via Samba. Along with support in the kernel the acl package is required to implement ACLs. It contains the utilities used to add modify remove and retrieve ACL information. The cp and mv commands copy or move any ACLs associated with files and directories. 4.1. Mounting File Systems Before using ACLs for a file or directory the partition for the file or directory must be mounted with ACL support. If it is a local ext3 file system it can mounted with the following command: mount -t ext3 -o acl device-name partition For example: mount -t ext3 -o acl /dev/VolGroup00/LogVol02 /work Alternatively if the partition is listed in the /etc/fstab file the entry for the partition can include the acl option: LABEL/work /work ext3 acl 1 2 If an ext3 file system is accessed via Samba and ACLs have been enabled for it the ACLs are recognized because Samba has been compiled with the --with-acl-support option. No special flags are required when accessing or mounting a Samba share. 4 .1.1. NFS By default if the file system being exported by an NFS server supports ACLs and the NFS client can read ACLs ACLs are utilized by the client system. To disable ACLs on NFS shares when configuring the server include the no_acl option in the /etc/exports file. To disable ACLs on an NFS share when mounting it on a client mount it with the no_acl option via the command line or the /etc/fstab file. 4.2. Setting Access ACLs There are two types of ACLs: access ACLs and default ACLs. An access ACL is the access control list for a specific file or directory. A default ACL can only be associated with a directory if a file within the directory does not have an access ACL it uses the rules of the default ACL for the directory. Default ACLs are optional. ACLs can be configured: 1. Per user Syst em Administ rat ors Guide 34

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2. Per group 3. Via the effective rights mask 4. For users not in the user group for the file The setfacl utility sets ACLs for files and directories. Use the -m option to add or modify the ACL of a file or directory: setfacl -m rules files Rules rules must be specified in the following formats. Multiple rules can be specified in the same command if they are separated by commas. u:uid:perms Sets the access ACL for a user. The user name or UID may be specified. The user may be any valid user on the system. g:gid:perms Sets the access ACL for a group. The group name or GID may be specified. The group may be any valid group on the system. m:perms Sets the effective rights mask. The mask is the union of all permissions of the owning group and all of the user and group entries. o:perms Sets the access ACL for users other than the ones in the group for the file. Permissions perms must be a combination of the characters r w and x for read write and execute. If a file or directory already has an ACL and the setfacl command is used the additional rules are added to the existing ACL or the existing rule is modified. Example 4 .1. Give read and write permissions For example to give read and write permissions to user andrius: setfacl -m u:andrius:rw /project/somefile To remove all the permissions for a user group or others use the -x option and do not specify any permissions: setfacl -x rules files Example 4 .2. Remove all permissions For example to remove all permissions from the user with UID 500: setfacl -x u:500 /project/somefile ⁠Chapt er 4 . Access Cont rol List s 35

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4.3. Setting Default ACLs To set a default ACL add d: before the rule and specify a directory instead of a file name. Example 4 .3. Setting default ACLs For example to set the default ACL for the /share/ directory to read and execute for users not in the user group an access ACL for an individual file can override it: setfacl -m d:o:rx /share 4.4. Retrieving ACLs To determine the existing ACLs for a file or directory use the getfacl command. In the example below the getfacl is used to determine the existing ACLs for a file. Example 4 .4 . Retrieving ACLs getfacl home/john/picture.png The above command returns the following output: file: home/john/picture.png owner: john group: john user::rw- group::r-- other::r-- If a directory with a default ACL is specified the default ACL is also displayed as illustrated below. For example getfacl home/sales/ will display similar output: file: home/sales/ owner: john group: john user::rw- user:barryg:r-- group::r-- mask::r-- other::r-- default:user::rwx default:user:john:rwx default:group::r-x default:mask::rwx default:other::r-x 4.5. Archiving File Systems With ACLs Syst em Administ rat ors Guide 36

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By default the dump command now preserves ACLs during a backup operation. When archiving a file or file system with tar use the --acls option to preserve ACLs. Similarly when using cp to copy files with ACLs include the --preservemode option to ensure that ACLs are copied across too. In addition the -a option equivalent to -dR --preserveall of cp also preserves ACLs during a backup along with other information such as timestamps SELinux contexts and the like. For more information about dump tar or cp refer to their respective man pages. The star utility is similar to the tar utility in that it can be used to generate archives of files however some of its options are different. Refer to Table 4.1 “Command Line Options for star” for a listing of more commonly used options. For all available options refer to man star. The star package is required to use this utility. Table 4 .1. Command Line Options for star Option Description -c Creates an archive file. -n Do not extract the files use in conjunction with -x to show what extracting the files does. -r Replaces files in the archive. The files are written to the end of the archive file replacing any files with the same path and file name. -t Displays the contents of the archive file. -u Updates the archive file. The files are written to the end of the archive if they do not exist in the archive or if the files are newer than the files of the same name in the archive. This option only works if the archive is a file or an unblocked tape that may backspace. -x Extracts the files from the archive. If used with -U and a file in the archive is older than the corresponding file on the file system the file is not extracted. -help Displays the most important options. -xhelp Displays the least important options. -/ Do not strip leading slashes from file names when extracting the files from an archive. By default they are stripped when files are extracted. -acl When creating or extracting archives or restores any ACLs associated with the files and directories. 4.6. Compatibility with Older Systems If an ACL has been set on any file on a given file system that file system has the ext_attr attribute. This attribute can be seen using the following command: tune2fs -l filesystem-device A file system that has acquired the ext_attr attribute can be mounted with older kernels but those kernels do not enforce any ACLs which have been set. Versions of the e2fsck utility included in version 1.22 and higher of the e2fsprogs package including the versions in Red Hat Enterprise Linux 2.1 and 4 can check a file system with the ext_attr attribute. Older versions refuse to check it. 4.7. ACL References ⁠Chapt er 4 . Access Cont rol List s 37

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4.7. ACL References Refer to the following man pages for more information. man acl — Description of ACLs man getfacl — Discusses how to get file access control lists man setfacl — Explains how to set file access control lists man star — Explains more about the star utility and its many options Syst em Administ rat ors Guide 38

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Chapter 5. Gaining Privileges System administrators and in some cases users need to perform certain tasks with administrative access. Accessing the system as the root user is potentially dangerous and can lead to widespread damage to the system and data. This chapter covers ways to gain administrative privileges using setuid programs such as su and sudo. These programs allow specific users to perform tasks which would normally be available only to the root user while maintaining a higher level of control and system security. See the Red Hat Enterprise Linux 7 Security Guide for more information on administrative controls potential dangers and ways to prevent data loss resulting from improper use of privileged access. 5.1. The su Command When a user executes the su command they are prompted for the root password and after authentication are given a root shell prompt. Once logged in using the su command the user is the root user and has absolute administrative access to the system. Note that this access is still subject to the restrictions imposed by SELinux if it is enabled. In addition once a user has become root it is possible for them to use the su command to change to any other user on the system without being prompted for a password. Because this program is so powerful administrators within an organization may want to limit who has access to the command. One of the simplest ways to do this is to add users to the special administrative group called wheel. To do this type the following command as root: usermod -a -G wheel username In the previous command replace username with the user name you want to add to the wheel group. You can also use the Users settings tool to modify group memberships as follows. Note that you need administrator privileges to perform this procedure. 1. Press the Super key to enter the Activities Overview type Users and then press Enter. The Users settings tool appears. The Super key appears in a variety of guises depending on the keyboard and other hardware but often as either the Windows or Command key and typically to the left of the Spacebar. 2. To enable making changes click the Unlock button and enter a valid administrator password. 3. Click a user icon in the left column to display the users properties in the right-hand pane. 4. Change the Account Type from Standard to Administrator. This will add the user to the wheel group. See Section 3.2 “Managing Users in a Graphical Environment” for more information about the Users tool. After you add the desired users to the wheel group it is advisable to only allow these specific users to use the su command. To do this edit the Pluggable Authentication Module PAM configuration file for su /etc/pam.d/su. Open this file in a text editor and uncomment the following line by removing the character: ⁠Chapt er 5. Gaining Privileges 39

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auth required pam_wheel.so use_uid This change means that only members of the administrative group wheel can switch to another user using the su command. Note The root user is part of the wheel group by default. 5.2. The sudo Command The sudo command offers another approach to giving users administrative access. When trusted users precede an administrative command with sudo they are prompted for their own password. Then when they have been authenticated and assuming that the command is permitted the administrative command is executed as if they were the root user. The basic format of the sudo command is as follows: sudo command In the above example command would be replaced by a command normally reserved for the root user such as mount. The sudo command allows for a high degree of flexibility. For instance only users listed in the /etc/sudoers configuration file are allowed to use the sudo command and the command is executed in the users shell not a root shell. This means the root shell can be completely disabled as shown in the Red Hat Enterprise Linux 7 Security Guide. Each successful authentication using the sudo command is logged to the file /var/log/messages and the command issued along with the issuers user name is logged to the file /var/log/secure. If additional logging is required use the pam_tty_audit module to enable TTY auditing for specified users by adding the following line to your /etc/pam.d/system-auth file: session required pam_tty_audit.so disablepattern enablepattern where pattern represents a comma-separated listing of users with an optional use of globs. For example the following configuration will enable TTY auditing for the root user and disable it for all other users: session required pam_tty_audit.so disable enableroot Important Configuring the pam_tty_audit PAM module for TTY auditing records only TTY input. This means that when the audited user logs in pam_tty_audit records the exact keystrokes the user makes into the /var/log/audit/audit.log file. For more information see the pam_tty_audit8 manual page. Syst em Administ rat ors Guide 4 0

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Another advantage of the sudo command is that an administrator can allow different users access to specific commands based on their needs. Administrators wanting to edit the sudo configuration file /etc/sudoers should use the visudo command. To give someone full administrative privileges type visudo and add a line similar to the following in the user privilege specification section: juan ALLALL ALL This example states that the user juan can use sudo from any host and execute any command. The example below illustrates the granularity possible when configuring sudo: users localhost/usr/sbin/shutdown -h now This example states that any member of the users system group can issue the command /sbin/shutdown -h now as long as it is issued from the console. The man page for sudoers has a detailed listing of options for this file. Important There are several potential risks to keep in mind when using the sudo command. You can avoid them by editing the /etc/sudoers configuration file using visudo as described above. Leaving the /etc/sudoers file in its default state gives every user in the wheel group unlimited root access. By default sudo stores the sudoers password for a five minute timeout period. Any subsequent uses of the command during this period will not prompt the user for a password. This could be exploited by an attacker if the user leaves his workstation unattended and unlocked while still being logged in. This behavior can be changed by adding the following line to the /etc/sudoers file: Defaults timestamp_timeoutvalue where value is the desired timeout length in minutes. Setting the value to 0 causes sudo to require a password every time. If a sudoers account is compromised an attacker can use sudo to open a new shell with administrative privileges: sudo /bin/bash Opening a new shell as root in this or similar fashion gives the attacker administrative access for a theoretically unlimited amount of time bypassing the timeout period specified in the /etc/sudoers file and never requiring the attacker to input a password for sudo again until the newly opened session is closed. 5.3. Additional Resources ⁠Chapt er 5. Gaining Privileges 4 1

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While programs allowing users to gain administrative privileges are a potential security risk security itself is beyond the scope of this particular book. You should therefore refer to the resources listed below for more information regarding security and privileged access. Installed Documentation su1 — The manual page for su provides information regarding the options available with this command. sudo8 — The manual page for sudo includes a detailed description of this command and lists options available for customizing its behavior. pam8 — The manual page describing the use of Pluggable Authentication Modules PAM for Linux. Online Documentation Red Hat Enterprise Linux 7 Security Guide — The Security Guide for Red Hat Enterprise Linux 7 provides a more in-depth look at potential security issues pertaining to setuid programs as well as techniques used to alleviate these risks. See Also Chapter 3 Managing Users and Groups documents how to manage system users and groups in the graphical user interface and on the command line. Syst em Administ rat ors Guide 4 2

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⁠Part II. Subscription and Support To receive updates to the software on a Red Hat Enterprise Linux system it must be subscribed to the Red Hat Content Delivery Network CDN and the appropriate repositories enabled. This part describes how to subscribe a system to the Red Hat Content Delivery Network. Red Hat provides support via the Customer Portal and you can access this support directly from the command line using the Red Hat Support Tool. This part describes the use of this command-line tool. ⁠Part II. Subscript ion and Support 4 3

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Chapter 6. Registering the System and Managing Subscriptions The subscription service provides a mechanism to handle Red Hat software inventory and allows you to install additional software or update already installed programs to newer versions using the yum package manager. In Red Hat Enterprise Linux 7 the recommended way to register your system and attach subscriptions is to use Red Hat Subscription Management. Note It is also possible to register the system and attach subscriptions after installation during the initial setup process. For detailed information about the initial setup see the Initial Setup chapter in the Installation Guide for Red Hat Enterprise Linux 7. Note that the Initial Setup application is only available on systems installed with the X Window System at the time of installation. 6.1. Registering the System and Attaching Subscriptions Complete the following steps to register your system and attach one or more subscriptions using Red Hat Subscription Management. Note that all subscription-manager commands are supposed to be run as root. 1. Run the following command to register your system. You will be prompted to enter your user name and password. Note that the user name and password are the same as your login credentials for Red Hat Customer Portal. subscription-manager register 2. Determine the pool ID of a subscription that you require. To do so type the following at a shell prompt to display a list of all subscriptions that are available for your system: subscription-manager list --available For each available subscription this command displays its name unique identifier expiration date and other details related to your subscription. To list subscriptions for all architectures add the --all option. The pool ID is listed on a line beginning with Pool ID. 3. Attach the appropriate subscription to your system by entering a command as follows: subscription-manager attach --poolpool_id Replace pool_id with the pool ID you determined in the previous step. To verify the list of subscriptions your system has currently attached at any time run: subscription-manager list --consumed For more details on how to register your system using Red Hat Subscription Management and associate it with subscriptions see the designated solution article. For comprehensive information about subscriptions see the Red Hat Subscription Management collection of guides. Syst em Administ rat ors Guide 4 4

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6.2. Managing Software Repositories When a system is subscribed to the Red Hat Content Delivery Network a repository file is created in the /etc/yum.repos.d/ directory. To verify that use yum to list all enabled repositories: yum repolist Red Hat Subscription Management also allows you to manually enable or disable software repositories provided by Red Hat. To list all available repositories use the following command: subscription-manager repos --list The repository names depend on the specific version of Red Hat Enterprise Linux you are using and are in the following format: rhel-variant-rhscl-version-rpms rhel-variant-rhscl-version-debug-rpms rhel-variant-rhscl-version-source-rpms Where variant is the Red Hat Enterprise Linux system variant server or workstation and version is the Red Hat Enterprise Linux system version 6 or 7 for example: rhel-server-rhscl-7-eus-rpms rhel-server-rhscl-7-eus-source-rpms rhel-server-rhscl-7-eus-debug-rpms To enable a repository enter a command as follows: subscription-manager repos --enable repository Replace repository with a name of the repository to enable. Similarly to disable a repository use the following command: subscription-manager repos --disable repository Section 8.5 “Configuring Yum and Yum Repositories” provides detailed information about managing software repositories using yum. 6.3. Removing Subscriptions To remove a particular subscription complete the following steps. 1. Determine the serial number of the subscription you want to remove by listing information about already attached subscriptions: subscription-manager list --consumed The serial number is the number listed as serial. For instance 744993814251016831 in the example below: ⁠Chapt er 6 . Regist ering t he Syst em and Managing Subscript ions 4 5

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SKU: ES0113909 Contract: 01234567 Account: 1234567 Serial: 744993814251016831 Pool ID: 8a85f9894bba16dc014bccdd905a5e23 Active: False Quantity Used: 1 Service Level: SELF-SUPPORT Service Type: L1-L3 Status Details: Subscription Type: Standard Starts: 02/27/2015 Ends: 02/27/2016 System Type: Virtual 2. Enter a command as follows to remove the selected subscription: subscription-manager remove --serialserial_number Replace serial_number with the serial number you determined in the previous step. To remove all subscriptions attached to the system run the following command: subscription-manager remove --all 6.4. Additional Resources For more information on how to register your system using Red Hat Subscription Management and associate it with subscriptions see the resources listed below. Installed Documentation subscription-manager8 — the manual page for Red Hat Subscription Management provides a complete list of supported options and commands. Related Books Red Hat Subscription Management collection of guides — These guides contain detailed information how to use Red Hat Subscription Management. Installation Guide — see the Initial Setup chapter for detailed information on how to register during the initial setup process. See Also Chapter 5 Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands. Chapter 8 Yum provides information about using the yum packages manager to install and update software. Syst em Administ rat ors Guide 4 6

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Chapter 7. Accessing Support Using the Red Hat Support Tool The Red Hat Support Tool in the redhat-support-tool package can function as both an interactive shell and as a single-execution program. It can be run over SSH or from any terminal. It enables for example searching the Red Hat Knowledgebase from the command line copying solutions directly on the command line opening and updating support cases and sending files to Red Hat for analysis. 7.1. Installing the Red Hat Support Tool The Red Hat Support Tool is installed by default on Red Hat Enterprise Linux. If required to ensure that it is enter the following command as root: yum install redhat-support-tool 7.2. Registering the Red Hat Support Tool Using the Command Line To register the Red Hat Support Tool to the customer portal using the command line proceed as follows: 1. redhat-support-tool config user username Where username is the user name of the Red Hat Customer Portal account. 2. redhat-support-tool config password Please enter the password for username: 7.3. Using the Red Hat Support Tool in Interactive Shell Mode To start the tool in interactive mode enter the following command: redhat-support-tool Welcome to the Red Hat Support Tool. Command for help: The tool can be run as an unprivileged user with a consequently reduced set of commands or as root. The commands can be listed by entering the character. The program or menu selection can be exited by entering the q or e character. You will be prompted for your Red Hat Customer Portal user name and password when you first search the Knowledgebase or support cases. Alternately set the user name and password for your Red Hat Customer Portal account using interactive mode and optionally save it to the configuration file. 7.4. Configuring the Red Hat Support Tool When in interactive mode the configuration options can be listed by entering the command config --help: ⁠Chapt er 7 . Accessing Support Using t he Red Hat Support T ool 4 7

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redhat-support-tool Welcome to the Red Hat Support Tool. Command for help: config --help Usage: config options config.option new option value Use the config command to set or get configuration file values. Options: -h --help show this help message and exit -g --global Save configuration option in /etc/redhat-support- tool.conf. -u --unset Unset configuration option. The configuration file options which can be set are: user : The Red Hat Customer Portal user. password : The Red Hat Customer Portal password. debug : CRITICAL ERROR WARNING INFO or DEBUG url : The support services URL. Defaulthttps://api.access.redhat.com proxy_url : A proxy server URL. proxy_user: A proxy server user. proxy_password: A password for the proxy server user. ssl_ca : Path to certificate authorities to trust during communication. kern_debug_dir: Path to the directory where kernel debug symbols should be downloaded and cached. Default/var/lib/redhat-support- tool/debugkernels Examples: - config user - config user my-rhn-username - config --unset user Procedure 7.1. Registering the Red Hat Support Tool Using Interactive Mode To register the Red Hat Support Tool to the customer portal using interactive mode proceed as follows: 1. Start the tool by entering the following command: redhat-support-tool 2. Enter your Red Hat Customer Portal user name: Command for help: config user username To save your user name to the global configuration file add the -g option. 3. Enter your Red Hat Customer Portal password: Command for help: config password Please enter the password for username: 7.4 .1. Saving Settings to the Configuration Files Syst em Administ rat ors Guide 4 8

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The Red Hat Support Tool unless otherwise directed stores values and options locally in the home directory of the current user using the /.redhat-support-tool/redhat-support- tool.conf configuration file. If required it is recommended to save passwords to this file because it is only readable by that particular user. When the tool starts it will read values from the global configuration file /etc/redhat-support-tool.conf and from the local configuration file. Locally stored values and options take precedence over globally stored settings. Warning It is recommended not to save passwords in the global /etc/redhat-support- tool.conf configuration file because the password is just base64 encoded and can easily be decoded. In addition the file is world readable. To save a value or option to the global configuration file add the -g --global option as follows: Command for help: config setting -g value Note In order to be able to save settings globally using the -g --global option the Red Hat Support Tool must be run as root because normal users do not have the permissions required to write to /etc/redhat-support-tool.conf. To remove a value or option from the local configuration file add the -u --unset option as follows: Command for help: config setting -u value This will clear unset the parameter from the tool and fall back to the equivalent setting in the global configuration file if available. Note When running as an unprivileged user values stored in the global configuration file cannot be removed using the -u --unset option but they can be cleared unset from the current running instance of the tool by using the -g --global option simultaneously with the -u --unset option. If running as root values and options can be removed from the global configuration file using -g --global simultaneously with the -u --unset option. 7.5. Opening and Updating Support Cases Using Interactive Mode Procedure 7.2. Opening a New Support Case Using Interactive Mode To open a new support case using interactive mode proceed as follows: 1. Start the tool by entering the following command: redhat-support-tool ⁠Chapt er 7 . Accessing Support Using t he Red Hat Support T ool 4 9

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2. Enter the opencase command: Command for help: opencase 3. Follow the on screen prompts to select a product and then a version. 4. Enter a summary of the case. 5. Enter a description of the case and press Ctrl+D on an empty line when complete. 6. Select a severity of the case. 7. Optionally chose to see if there is a solution to this problem before opening a support case. 8. Confirm you would still like to open the support case. Support case 0123456789 has successfully been opened 9. Optionally chose to attach an SOS report. 10. Optionally chose to attach a file. Procedure 7.3. Viewing and Updating an Existing Support Case Using Interactive Mode To view and update an existing support case using interactive mode proceed as follows: 1. Start the tool by entering the following command: redhat-support-tool 2. Enter the getcase command: Command for help: getcase case-number Where case-number is the number of the case you want to view and update. 3. Follow the on screen prompts to view the case modify or add comments and get or add attachments. Procedure 7.4 . Modifying an Existing Support Case Using Interactive Mode To modify the attributes of an existing support case using interactive mode proceed as follows: 1. Start the tool by entering the following command: redhat-support-tool 2. Enter the modifycase command: Command for help: modifycase case-number Where case-number is the number of the case you want to view and update. 3. The modify selection list appears: Syst em Administ rat ors Guide 50

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Type the number of the attribute to modify or e to return to the previous menu. 1 Modify Type 2 Modify Severity 3 Modify Status 4 Modify Alternative-ID 5 Modify Product 6 Modify Version End of options. Follow the on screen prompts to modify one or more of the options. 4. For example to modify the status enter 3: Selection: 3 1 Waiting on Customer 2 Waiting on Red Hat 3 Closed Please select a status or q to exit: 7.6. Viewing Support Cases on the Command Line Viewing the contents of a case on the command line provides a quick and easy way to apply solutions from the command line. To view an existing support case on the command line enter a command as follows: redhat-support-tool getcase case-number Where case-number is the number of the case you want to download. 7.7. Additional Resources The Red Hat Knowledgebase article Red Hat Support Tool has additional information examples and video tutorials. ⁠Chapt er 7 . Accessing Support Using t he Red Hat Support T ool 51

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⁠Part III. Installing and Managing Software All software on a Red Hat Enterprise Linux system is divided into RPM packages which can be installed upgraded or removed. This part describes how to manage packages on Red Hat Enterprise Linux using Yum. Syst em Administ rat ors Guide 52

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Chapter 8. Yum Yum is the Red Hat package manager that is able to query for information about available packages fetch packages from repositories install and uninstall them and update an entire system to the latest available version. Yum performs automatic dependency resolution when updating installing or removing packages and thus is able to automatically determine fetch and install all available dependent packages. Yum can be configured with new additional repositories or package sources and also provides many plug-ins which enhance and extend its capabilities. Yum is able to perform many of the same tasks that RPM can additionally many of the command-line options are similar. Yum enables easy and simple package management on a single machine or on groups of them. The following sections assume your system was registered with Red Hat Subscription Management during installation as described in the Red Hat Enterprise Linux 7 Installation Guide. If your system is not subscribed see Chapter 6 Registering the System and Managing Subscriptions. Important Yum provides secure package management by enabling GPG Gnu Privacy Guard also known as GnuPG signature verification on GPG-signed packages to be turned on for all package repositories package sources or for individual repositories. When signature verification is enabled yum will refuse to install any packages not GPG-signed with the correct key for that repository. This means that you can trust that the RPM packages you download and install on your system are from a trusted source such as Red Hat and were not modified during transfer. See Section 8.5 “Configuring Yum and Yum Repositories” for details on enabling signature-checking with yum or Section A.3.2 “Checking Package Signatures” for information on working with and verifying GPG-signed RPM packages in general. Yum also enables you to easily set up your own repositories of RPM packages for download and installation on other machines. When possible yum uses parallel download of multiple packages and metadata to speed up downloading. Learning yum is a worthwhile investment because it is often the fastest way to perform system administration tasks and it provides capabilities beyond those provided by the PackageKit graphical package management tools. Note You must have superuser privileges in order to use yum to install update or remove packages on your system. All examples in this chapter assume that you have already obtained superuser privileges by using either the su or sudo command. 8.1. Checking For and Updating Packages Yum enables you to check if your system has any updates waiting to be applied. You can list packages that need to be updated and update them as a whole or you can update a selected individual package. 8.1.1. Checking For Updates ⁠Chapt er 8 . Yum 53

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To see which installed packages on your system have updates available use the following command: yum check-update Example 8.1. Example output of the yum check-update command The output of yum check-update can look as follows: yum check-update Loaded plugins: product-id search-disabled-repos subscription-manager dracut.x86_64 033-360.el7_2 rhel-7- server-rpms dracut-config-rescue.x86_64 033-360.el7_2 rhel-7-server- rpms kernel.x86_64 3.10.0-327.el7 rhel-7-server- rpms rpm.x86_64 4.11.3-17.el7 rhel-7-server- rpms rpm-libs.x86_64 4.11.3-17.el7 rhel-7-server- rpms rpm-python.x86_64 4.11.3-17.el7 rhel-7-server- rpms yum.noarch 3.4.3-132.el7 rhel-7-server- rpms The packages in the above output are listed as having updates available. The first package in the list is dracut. Each line in the example output consists of several rows in case of dracut: dracut — the name of the package x86_64 — the CPU architecture the package was built for 033 — the version of the updated package to be installed 360.el7 — the release of the updated package _2 — a build version added as part of a z-stream update rhel-7-server-rpms — the repository in which the updated package is located. The output also shows that we can update the kernel the kernel package yum and RPM themselves the yum and rpm packages as well as their dependencies such as the rpm-libs and rpm-python packages all using the yum command. 8.1.2. Updating Packages You can choose to update a single package multiple packages or all packages at once. If any dependencies of the package or packages you update have updates available themselves then they are updated too. Updat ing a Single Package To update a single package run the following command as root: Syst em Administ rat ors Guide 54

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yum update package_name Example 8.2. Updating the rpm package To update the rpm package type: yum update rpm Loaded plugins: langpacks product-id subscription-manager Updating Red Hat repositories. INFO:rhsm-app.repolib:repos updated: 0 Setting up Update Process Resolving Dependencies -- Running transaction check --- Package rpm.x86_64 0:4.11.1-3.el7 will be updated -- Processing Dependency: rpm 4.11.1-3.el7 for package: rpm-libs- 4.11.1-3.el7.x86_64 -- Processing Dependency: rpm 4.11.1-3.el7 for package: rpm-python- 4.11.1-3.el7.x86_64 -- Processing Dependency: rpm 4.11.1-3.el7 for package: rpm-build- 4.11.1-3.el7.x86_64 --- Package rpm.x86_64 0:4.11.2-2.el7 will be an update -- Running transaction check ... -- Finished Dependency Resolution Dependencies Resolved Package Arch Version Repository Size Updating: rpm x86_64 4.11.2-2.el7 rhel 1.1 M Updating for dependencies: rpm-build x86_64 4.11.2-2.el7 rhel 139 k rpm-build-libs x86_64 4.11.2-2.el7 rhel 98 k rpm-libs x86_64 4.11.2-2.el7 rhel 261 k rpm-python x86_64 4.11.2-2.el7 rhel 74 k Transaction Summary Upgrade 1 Package +4 Dependent packages Total size: 1.7 M Is this ok y/d/N: This output contains several items of interest: ⁠Chapt er 8 . Yum 55

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1. Loaded plugins: langpacks product-id subscription-manager — Yum always informs you which yum plug-ins are installed and enabled. See Section 8.6 “Yum Plug-ins” for general information on yum plug-ins or Section 8.6.3 “Working with Yum Plug-ins” for descriptions of specific plug-ins. 2. rpm.x86_64 — you can download and install a new rpm package as well as its dependencies. Transaction check is performed for each of these packages. 3. Yum presents the update information and then prompts you for confirmation of the update yum runs interactively by default. If you already know which transactions the yum command plans to perform you can use the -y option to automatically answer yes to any questions that yum asks in which case it runs non-interactively. However you should always examine which changes yum plans to make to the system so that you can easily troubleshoot any problems that might arise. You can also choose to download the package without installing it. To do so select the d option at the download prompt. This launches a background download of the selected package. If a transaction fails you can view yum transaction history by using the yum history command as described in Section 8.4 “Working with Transaction History”. Important Yum always installs a new kernel regardless of whether you are using the yum update or yum install command. When using RPM on the other hand it is important to use the rpm -i kernel command which installs a new kernel instead of rpm -u kernel which replaces the current kernel. See Section A.2.1 “Installing and Upgrading Packages” for more information on installing and upgrading kernels with RPM. Similarly it is possible to update a package group. Type as root: yum group update group_name Here replace group_name with a name of the package group you want to update. For more information on package groups see Section 8.3 “Working with Package Groups”. Yum also offers the upgrade command that is equal to update with enabled obsoletes configuration option see Section 8.5.1 “Setting main Options”. By default obsoletes is turned on in /etc/yum.conf which makes these two commands equivalent. Updat ing All Packages and T heir Dependencies To update all packages and their dependencies use the yum update command without any arguments: yum update Updat ing Securit y-Relat ed Packages If packages have security updates available you can update only these packages to their latest versions. Type as root: Syst em Administ rat ors Guide 56

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yum update --security You can also update packages only to versions containing the latest security updates. Type as root: yum update-minimal --security For example assume that: the kernel-3.10.0-1 package is installed on your system the kernel-3.10.0-2 package was released as a security update the kernel-3.10.0-3 package was released as a bug fix update. Then yum update-minimal --security updates the package to kernel-3.10.0-2 and yum update --security updates the package to kernel-3.10.0-3. 8.1.3. Preserving Configuration File Changes You will inevitably make changes to the configuration files installed by packages as you use your Red Hat Enterprise Linux system. RPM which yum uses to perform changes to the system provides a mechanism for ensuring their integrity. See Section A.2.1 “Installing and Upgrading Packages” for details on how to manage changes to configuration files across package upgrades. 8.1.4 . Upgrading the System Off-line with ISO and Yum For systems that are disconnected from the Internet or Red Hat Network using the yum update command with the Red Hat Enterprise Linux installation ISO image is an easy and quick way to upgrade systems to the latest minor version. The following steps illustrate the upgrading process: 1. Create a target directory to mount your ISO image. This directory is not automatically created when mounting so create it before proceeding to the next step. As root type: mkdir mount_dir Replace mount_dir with a path to the mount directory. Typically users create it as a subdirectory in the /media directory. 2. Mount the Red Hat Enterprise Linux 7 installation ISO image to the previously created target directory. As root type: mount -o loop iso_name mount_dir Replace iso_name with a path to your ISO image and mount_dir with a path to the target directory. Here the -o loop option is required to mount the file as a block device. 3. Copy the media.repo file from the mount directory to the /etc/yum.repos.d/ directory. Note that configuration files in this directory must have the .repo extension to function properly. cp mount_dir/media.repo /etc/yum.repos.d/new.repo This creates a configuration file for the yum repository. Replace new.repo with the filename for example rhel7.repo. ⁠Chapt er 8 . Yum 57

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4. Edit the new configuration file so that it points to the Red Hat Enterprise Linux installation ISO. Add the following line into the /etc/yum.repos.d/new.repo file: baseurlfile:///mount_dir Replace mount_dir with a path to the mount point. 5. Update all yum repositories including /etc/yum.repos.d/new.repo created in previous steps. As root type: yum update This upgrades your system to the version provided by the mounted ISO image. 6. After successful upgrade you can unmount the ISO image. As root type: umount mount_dir where mount_dir is a path to your mount directory. Also you can remove the mount directory created in the first step. As root type: rmdir mount_dir 7. If you will not use the previously created configuration file for another installation or update you can remove it. As root type: rm /etc/yum.repos.d/new.repo Example 8.3. Upgrading from Red Hat Enterprise Linux 7.0 to 7.1 If required to upgrade a system without access to the Internet using an ISO image with the newer version of the system called for example rhel-server-7.1-x86_64-dvd.iso create a target directory for mounting such as /media/rhel7/. As root change into the directory with your ISO image and type: mount -o loop rhel-server-7.1-x86_64-dvd.iso /media/rhel7/ Then set up a yum repository for your image by copying the media.repo file from the mount directory: cp /media/rhel7/media.repo /etc/yum.repos.d/rhel7.repo To make yum recognize the mount point as a repository add the following line into the /etc/yum.repos.d/rhel7.repo copied in the previous step: baseurlfile:///media/rhel7/ Now updating the yum repository will upgrade your system to a version provided by rhel- server-7.1-x86_64-dvd.iso. As root execute: yum update Syst em Administ rat ors Guide 58

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When your system is successfully upgraded you can unmount the image remove the target directory and the configuration file: umount /media/rhel7/ rmdir /media/rhel7/ rm /etc/yum.repos.d/rhel7.repo 8.2. Working with Packages Yum enables you to perform a complete set of operations with software packages including searching for packages viewing information about them installing and removing. 8.2.1. Searching Packages You can search all RPM package names descriptions and summaries by using the following command: yum search term… Replace term with a package name you want to search. Example 8.4 . Searching for packages matching a specific string To list all packages that match “vim” “gvim” or “emacs” type: yum search vim gvim emacs Loaded plugins: langpacks product-id search-disabled-repos subscription-manager N/S matched: vim vim-X11.x86_64 : The VIM version of the vi editor for the X Window System vim-common.x86_64 : The common files needed by any version of the VIM editor output truncated N/S matched: emacs emacs.x86_64 : GNU Emacs text editor emacs-auctex.noarch : Enhanced TeX modes for Emacs output truncated Name and summary matches mostly use "search all" for everything. Warning: No matches found for: gvim The yum search command is useful for searching for packages you do not know the name of but for which you know a related term. Note that by default yum search returns matches in package name and summary which makes the search faster. Use the yum search all command for a more ⁠Chapt er 8 . Yum 59

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exhaustive but slower search. Filt ering t he Result s All of yums list commands allow you to filter the results by appending one or more glob expressions as arguments. Glob expressions are normal strings of characters which contain one or more of the wildcard characters which expands to match any character subset and which expands to match any single character. Be careful to escape the glob expressions when passing them as arguments to a yum command otherwise the Bash shell will interpret these expressions as pathname expansions and potentially pass all files in the current directory that match the global expressions to yum. To make sure the glob expressions are passed to yum as intended use one of the following methods: escape the wildcard characters by preceding them with a backslash character double-quote or single-quote the entire glob expression. Examples in the following section demonstrate usage of both these methods. 8.2.2. Listing Packages To list information on all installed and available packages type the following at a shell prompt: yum list all To list installed and available packages that match inserted glob expressions use the following command: yum list glob_expression… Example 8.5. Listing ABRT-related packages Packages with various ABRT add-ons and plug-ins either begin with “abrt-addon-” or “abrt- plugin-”. To list these packages type the following command at a shell prompt. Note how the wildcard characters are escaped with a backslash character: yum list abrt-addon\ abrt-plugin\ Loaded plugins: langpacks product-id search-disabled-repos subscription-manager Installed Packages abrt-addon-ccpp.x86_64 2.1.11-35.el7 rhel-7-server-rpms abrt-addon-kerneloops.x86_64 2.1.11-35.el7 rhel-7-server-rpms abrt-addon-pstoreoops.x86_64 2.1.11-35.el7 rhel-7-server-rpms abrt-addon-python.x86_64 2.1.11-35.el7 rhel-7-server-rpms abrt-addon-vmcore.x86_64 2.1.11-35.el7 rhel-7-server-rpms abrt-addon-xorg.x86_64 2.1.11-35.el7 rhel-7-server-rpms Syst em Administ rat ors Guide 60

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To list all packages installed on your system use the installed keyword. The rightmost column in the output lists the repository from which the package was retrieved. yum list installed glob_expression… Example 8.6 . Listing all installed versions of the krb package The following example shows how to list all installed packages that begin with “krb” followed by exactly one character and a hyphen. This is useful when you want to list all versions of certain component as these are distinguished by numbers. The entire glob expression is quoted to ensure proper processing. yum list installed "krb-" Loaded plugins: langpacks product-id search-disabled-repos subscription-manager Installed Packages krb5-libs.x86_64 1.13.2-10.el7 rhel-7-server-rpms To list all packages in all enabled repositories that are available to install use the command in the following form: yum list available glob_expression… Example 8.7. Listing available gstreamer plug-ins For instance to list all available packages with names that contain “gstreamer” and then “plugin” run the following command: yum list available gstreamer\plugin\ Loaded plugins: langpacks product-id search-disabled-repos subscription-manager Available Packages gstreamer-plugins-bad-free.i686 0.10.23-20.el7 rhel-7-server-rpms gstreamer-plugins-base.i686 0.10.36-10.el7 rhel-7-server-rpms gstreamer-plugins-good.i686 0.10.31-11.el7 rhel-7-server-rpms gstreamer1-plugins-bad-free.i686 1.4.5-3.el7 rhel-7-server-rpms gstreamer1-plugins-base.i686 1.4.5-2.el7 rhel-7-server-rpms gstreamer1-plugins-base-devel.i686 1.4.5-2.el7 rhel-7-server-rpms gstreamer1-plugins-base-devel.x86_64 1.4.5-2.el7 rhel-7-server-rpms gstreamer1-plugins-good.i686 1.4.5-2.el7 rhel-7-server-rpms ⁠Chapt er 8 . Yum 61

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List ing Repo sit o ries To list the repository ID name and number of packages for each enabled repository on your system use the following command: yum repolist To list more information about these repositories add the -v option. With this option enabled information including the file name overall size date of the last update and base URL are displayed for each listed repository. As an alternative you can use the repoinfo command that produces the same output. yum repolist -v yum repoinfo To list both enabled and disabled repositories use the following command. A status column is added to the output list to show which of the repositories are enabled. yum repolist all By passing disabled as a first argument you can reduce the command output to disabled repositories. For further specification you can pass the ID or name of repositories or related glob_expressions as arguments. Note that if there is an exact match between the repository ID or name and the inserted argument this repository is listed even if it does not pass the enabled or disabled filter. 8.2.3. Displaying Package Information To display information about one or more packages use the following command glob expressions are valid here as well: yum info package_name… Replace package_name with the name of the package. Example 8.8. Displaying information on the abrt package To display information about the abrt package type: yum info abrt Loaded plugins: langpacks product-id search-disabled-repos subscription-manager Installed Packages Name : abrt Arch : x86_64 Version : 2.1.11 Release : 35.el7 Size : 2.3 M Repo : installed From repo : rhel-7-server-rpms Summary : Automatic bug detection and reporting tool URL : https://fedorahosted.org/abrt/ Syst em Administ rat ors Guide 62

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License : GPLv2+ Description : abrt is a tool to help users to detect defects in applications and : to create a bug report with all information needed by maintainer to fix : it. It uses plugin system to extend its functionality. The yum info package_name command is similar to the rpm -q --info package_name command but provides as additional information the name of the yum repository the RPM package was installed from look for the From repo: line in the output. Using yumdb You can also query the yum database for alternative and useful information about a package by using the following command: yumdb info package_name This command provides additional information about a package including the checksum of the package and the algorithm used to produce it such as SHA-256 the command given on the command line that was invoked to install the package if any and the reason why the package is installed on the system where user indicates it was installed by the user and dep means it was brought in as a dependency. Example 8.9 . Querying yumdb for information on the yum package To display additional information about the yum package type: yumdb info yum Loaded plugins: langpacks product-id yum-3.4.3-132.el7.noarch changed_by 1000 checksum_data a9d0510e2ff0d04d04476c693c0313a11379053928efd29561f9a837b3d9eb02 checksum_type sha256 command_line upgrade from_repo rhel-7-server-rpms from_repo_revision 1449144806 from_repo_timestamp 1449144805 installed_by 4294967295 origin_url https://cdn.redhat.com/content/dist/rhel/server/7/7Server/x86_64/os/Pac kages/yum-3.4.3-132.el7.noarch.rpm reason user releasever 7Server var_uuid 147a7d49-b60a-429f-8d8f-3edb6ce6f4a1 For more information on the yumdb command see the yumdb8 manual page. 8.2.4 . Installing Packages ⁠Chapt er 8 . Yum 63

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To install a single package and all of its non-installed dependencies enter a command in the following form as root: yum install package_name You can also install multiple packages simultaneously by appending their names as arguments. To do so type as root: yum install package_name package_name… If you are installing packages on a multilib system such as an AMD64 or Intel64 machine you can specify the architecture of the package as long as it is available in an enabled repository by appending .arch to the package name: yum install package_name.arch Example 8.10. Installing packages on multilib system To install the sqlite package for the i686 architecture type: yum install sqlite.i686 You can use glob expressions to quickly install multiple similarly named packages. Execute as root: yum install glob_expression… Example 8.11. Installing all audacious plugins Global expressions are useful when you want to install several packages with similar names. To install all audacious plug-ins use the command in the following form: yum install audacious-plugins-\ In addition to package names and glob expressions you can also provide file names to yum install. If you know the name of the binary you want to install but not its package name you can give yum install the path name. As root type: yum install /usr/sbin/named Yum then searches through its package lists finds the package which provides /usr/sbin/named if any and prompts you as to whether you want to install it. As you can see in the above examples the yum install command does not require strictly defined arguments. It can process various formats of package names and glob expressions which makes installation easier for users. On the other hand it takes some time until yum parses the input correctly especially if you specify a large number of packages. To optimize the package search you can use the following commands to explicitly define how to parse the arguments: yum install-n name Syst em Administ rat ors Guide 64

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yum install-na name.architecture yum install-nevra name-epoch:version-release.architecture With install-n yum interprets name as the exact name of the package. The install-na command tells yum that the subsequent argument contains the package name and architecture divided by the dot character. With install-nevra yum will expect an argument in the form name- epoch:version-release.architecture. Similarly you can use yum remove-n yum remove-na and yum remove-nevra when searching for packages to be removed. Note If you know you want to install the package that contains the named binary but you do not know in which bin/ or sbin/ directory the file is installed use the yum provides command with a glob expression: yum provides "bin/named" Loaded plugins: langpacks product-id search-disabled-repos subscription- : manager 32:bind-9.9.4-14.el7.x86_64 : The Berkeley Internet Name Domain BIND DNS : Domain Name System server Repo : rhel-7-server-rpms Matched from: Filename : /usr/sbin/named yum provides "/file_name" is a useful way to find the packages that contain file_name. Example 8.12. Installation Process The following example provides an overview of installation with use of yum. To download and install the latest version of the httpd package execute as root: yum install httpd Loaded plugins: langpacks product-id subscription-manager Resolving Dependencies -- Running transaction check --- Package httpd.x86_64 0:2.4.6-12.el7 will be updated --- Package httpd.x86_64 0:2.4.6-13.el7 will be an update -- Processing Dependency: 2.4.6-13.el7 for package: httpd-2.4.6- 13.el7.x86_64 -- Running transaction check --- Package httpd-tools.x86_64 0:2.4.6-12.el7 will be updated --- Package httpd-tools.x86_64 0:2.4.6-13.el7 will be an update -- Finished Dependency Resolution Dependencies Resolved ⁠Chapt er 8 . Yum 65

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After executing the above command yum loads the necessary plug-ins and runs the transaction check. In this case httpd is already installed. Since the installed package is older than the latest currently available version it will be updated. The same applies to the httpd-tools package that httpd depends on. Then a transaction summary is displayed: Package Arch Version Repository Size Updating: httpd x86_64 2.4.6-13.el7 rhel-x86_64-server-7 1.2 M Updating for dependencies: httpd-tools x86_64 2.4.6-13.el7 rhel-x86_64-server-7 77 k Transaction Summary Upgrade 1 Package +1 Dependent package Total size: 1.2 M Is this ok y/d/N: In this step yum prompts you to confirm the installation. Apart from y yes and N no options you can choose d download only to download the packages but not to install them directly. If you choose y the installation proceeds with the following messages until it is finished successfully. Downloading packages: Running transaction check Running transaction test Transaction test succeeded Running transaction Updating : httpd-tools-2.4.6-13.el7.x86_64 1/4 Updating : httpd-2.4.6-13.el7.x86_64 2/4 Cleanup : httpd-2.4.6-12.el7.x86_64 3/4 Cleanup : httpd-tools-2.4.6-12.el7.x86_64 4/4 Verifying : httpd-2.4.6-13.el7.x86_64 1/4 Verifying : httpd-tools-2.4.6-13.el7.x86_64 2/4 Verifying : httpd-tools-2.4.6-12.el7.x86_64 3/4 Verifying : httpd-2.4.6-12.el7.x86_64 4/4 Updated: httpd.x86_64 0:2.4.6-13.el7 Syst em Administ rat ors Guide 66

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Dependency Updated: httpd-tools.x86_64 0:2.4.6-13.el7 Complete To install a previously downloaded package from the local directory on your system use the following command: yum localinstall path Replace path with the path to the package you want to install. 8.2.5. Downloading Packages As shown in Example 8.12 “Installation Process” at a certain point of installation process you are prompted to confirm the installation with the following message: ... Total size: 1.2 M Is this ok y/d/N: ... With the d option yum downloads the packages without installing them immediately. You can install these packages later offline with the yum localinstall command or you can share them with a different device. Downloaded packages are saved in one of the subdirectories of the cache directory by default ⁠/var/cache/yum/basearch/releasever/packages/. The downloading proceeds in background mode so that you can use yum for other operations in parallel. 8.2.6. Removing Packages Similarly to package installation yum enables you to uninstall them. To uninstall a particular package as well as any packages that depend on it run the following command as root: yum remove package_name… As when you install multiple packages you can remove several at once by adding more package names to the command. Example 8.13. Removing several packages To remove totem type the following at a shell prompt: yum remove totem Similar to install remove can take these arguments: package names glob expressions file lists ⁠Chapt er 8 . Yum 67

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package provides Warning Yum is not able to remove a package without also removing packages which depend on it. This type of operation which can only be performed by RPM is not advised and can potentially leave your system in a non-functioning state or cause applications to not work correctly or crash. For further information see Section A.2.2 “Uninstalling Packages” in the RPM chapter. 8.3. Working with Package Groups A package group is a collection of packages that serve a common purpose for instance System Tools or Sound and Video. Installing a package group pulls a set of dependent packages saving time considerably. The yum groups command is a top-level command that covers all the operations that act on package groups in yum. 8.3.1. Listing Package Groups The summary option is used to view the number of installed groups available groups available environment groups and both installed and available language groups: yum groups summary Example 8.14 . Example output of yum groups summary yum groups summary Loaded plugins: langpacks product-id subscription-manager Available Environment Groups: 12 Installed Groups: 10 Available Groups: 12 To list all package groups from yum repositories add the list option. You can filter the command output by group names. yum group list glob_expression… Several optional arguments can be passed to this command including hidden to list also groups not marked as user visible and ids to list group IDs. You can add language environment installed or available options to reduce the command output to a specific group type. To list mandatory and optional packages contained in a particular group use the following command: yum group info glob_expression… Example 8.15. Viewing information on the LibreOffice package group Syst em Administ rat ors Guide 68

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yum group info LibreOffice Loaded plugins: langpacks product-id subscription-manager Group: LibreOffice Group-Id: libreoffice Description: LibreOffice Productivity Suite Mandatory Packages: libreoffice-calc libreoffice-draw -libreoffice-emailmerge libreoffice-graphicfilter libreoffice-impress libreoffice-math libreoffice-writer +libreoffice-xsltfilter Optional Packages: libreoffice-base libreoffice-pyuno As you can see in the above example the packages included in the package group can have different states that are marked with the following symbols: " - " — Package is not installed and it will not be installed as a part of the package group. " + " — Package is not installed but it will be installed on the next yum upgrade or yum group upgrade. " " — Package is installed and it was installed as a part of the package group. no symbol — Package is installed but it was installed outside of the package group. This means that the yum group remove will not remove these packages. These distinctions take place only when the group_command configuration parameter is set to objects which is the default setting. Set this parameter to a different value if you do not want yum to track if a package was installed as a part of the group or separately which will make "no symbol" packages equivalent to "" packages. You can alter the above package states using the yum group mark command. For example yum group mark packages marks any given installed packages as members of a specified group. To avoid installation of new packages on group update use yum group mark blacklist. See the yum8 man page for more information on capabilities of yum group mark. Note You can identify an environmental group with use of the prefix and a package group can be marked with . When using yum group list info install or remove pass group_name to specify a package group group_name to specify an environmental group or group_name to include both. 8.3.2. Installing a Package Group Each package group has a name and a group ID groupid. To list the names of all package groups and their group IDs which are displayed in parentheses type: ⁠Chapt er 8 . Yum 69

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yum group list ids Example 8.16 . Finding name and groupid of a package group To find the name or ID of a package group for example a group related to the KDE desktop environment type: yum group list ids kde\ Available environment groups: KDE Plasma Workspaces kde-desktop-environment Done Some groups are hidden by settings in the configured repositories. For example on a server make use of the hidden command option to list hidden groups too: yum group list hidden ids kde\ Loaded plugins: product-id subscription-manager Available Groups: KDE kde-desktop Done You can install a package group by passing its full group name without the groupid part to the group install command. As root type: yum group install "group name" You can also install by groupid. As root execute the following command: yum group install groupid You can pass the groupid or quoted group name to the install command if you prepend it with an symbol which tells yum that you want to perform group install. As root type: yum install group Replace group with the groupid or quoted group name. The same logic applies to environmental groups: yum install group Example 8.17. Four equivalent ways of installing the KDE Desktop group As mentioned before you can use four alternative but equivalent ways to install a package group. For KDE Desktop the commands look as follows: yum group install "KDE Desktop" yum group install kde-desktop yum install "KDE Desktop" yum install kde-desktop Syst em Administ rat ors Guide 70

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8.3.3. Removing a Package Group You can remove a package group using syntax similar to the install syntax with use of either name of the package group or its id. As root type: yum group remove group_name yum group remove groupid Also you can pass the groupid or quoted name to the remove command if you prepend it with an - symbol which tells yum that you want to perform group remove. As root type: yum remove group Replace group with the groupid or quoted group name. Similarly you can replace an environmental group: yum remove group Example 8.18. Four equivalent ways of removing the KDE Desktop group Similarly to install you can use four alternative but equivalent ways to remove a package group. For KDE Desktop the commands look as follows: yum group remove "KDE Desktop" yum group remove kde-desktop yum remove "KDE Desktop" yum remove kde-desktop 8.4. Working with Transaction History The yum history command enables users to review information about a timeline of yum transactions the dates and times they occurred the number of packages affected whether these transactions succeeded or were aborted and if the RPM database was changed between transactions. Additionally this command can be used to undo or redo certain transactions. All history data is stored in the history DB in the /var/lib/yum/history/ directory. 8.4 .1. Listing T ransactions To display a list of the twenty most recent transactions as root either run yum history with no additional arguments or type the following at a shell prompt: yum history list To display all transactions add the all keyword: yum history list all To display only transactions in a given range use the command in the following form: ⁠Chapt er 8 . Yum 71

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yum history list start_id..end_id You can also list only transactions regarding a particular package or packages. To do so use the command with a package name or a glob expression: yum history list glob_expression… Example 8.19 . Listing the five oldest transactions In the output of yum history list the most recent transaction is displayed at the top of the list. To display information about the five oldest transactions stored in the history data base type: yum history list 1..5 Loaded plugins: langpacks product-id subscription-manager ID | Login user | Date and time | Actions | Altered ---------------------------------------------------------------------- --------- 5 | User user | 2013-07-29 15:33 | Install | 1 4 | User user | 2013-07-21 15:10 | Install | 1 3 | User user | 2013-07-16 15:27 | I U | 73 2 | System unset | 2013-07-16 15:19 | Update | 1 1 | System unset | 2013-07-16 14:38 | Install | 1106 history list All forms of the yum history list command produce tabular output with each row consisting of the following columns: ID — an integer value that identifies a particular transaction. Login user — the name of the user whose login session was used to initiate a transaction. This information is typically presented in the Full Name username form. For transactions that were not issued by a user such as an automatic system update System unset is used instead. Date and time — the date and time when a transaction was issued. Actions — a list of actions that were performed during a transaction as described in Table 8.1 “Possible values of the Actions field”. Altered — the number of packages that were affected by a transaction possibly followed by additional information as described in Table 8.2 “Possible values of the Altered field”. Table 8.1. Possible values of the Actions field Action Abbreviati on Description Downgrade D At least one package has been downgraded to an older version. Syst em Administ rat ors Guide 72

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Erase E At least one package has been removed. Install I At least one new package has been installed. Obsoleting O At least one package has been marked as obsolete. Reinstall R At least one package has been reinstalled. Update U At least one package has been updated to a newer version. Action Abbreviati on Description Table 8.2. Possible values of the Altered field Symbol Description Before the transaction finished the rpmdb database was changed outside yum. After the transaction finished the rpmdb database was changed outside yum. The transaction failed to finish. The transaction finished successfully but yum returned a non-zero exit code. E The transaction finished successfully but an error or a warning was displayed. P The transaction finished successfully but problems already existed in the rpmdb database. s The transaction finished successfully but the --skip-broken command-line option was used and certain packages were skipped. To synchronize the rpmdb or yumdb database contents for any installed package with the currently used rpmdb or yumdb database type the following: yum history sync To display some overall statistics about the currently used history database use the following command: yum history stats Example 8.20. Example output of yum history stats yum history stats Loaded plugins: langpacks product-id subscription-manager File : //var/lib/yum/history/history-2012-08-15.sqlite Size : 2766848 Transactions: 41 Begin time : Wed Aug 15 16:18:25 2012 End time : Wed Feb 27 14:52:30 2013 Counts : NEVRAC : 2204 NEVRA : 2204 NA : 1759 ⁠Chapt er 8 . Yum 73

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NEVR : 2204 rpm DB : 2204 yum DB : 2204 history stats Yum also enables you to display a summary of all past transactions. To do so run the command in the following form as root: yum history summary To display only transactions in a given range type: yum history summary start_id..end_id Similarly to the yum history list command you can also display a summary of transactions regarding a certain package or packages by supplying a package name or a glob expression: yum history summary glob_expression… Example 8.21. Summary of the five latest transactions yum history summary 1..5 Loaded plugins: langpacks product-id subscription-manager Login user | Time | Actions | Altered ---------------------------------------------------------------------- --------- Jaromir ... jhradilek | Last day | Install | 1 Jaromir ... jhradilek | Last week | Install | 1 Jaromir ... jhradilek | Last 2 weeks | I U | 73 System unset | Last 2 weeks | I U | 1107 history summary All forms of the yum history summary command produce simplified tabular output similar to the output of yum history list. As shown above both yum history list and yum history summary are oriented towards transactions and although they allow you to display only transactions related to a given package or packages they lack important details such as package versions. To list transactions from the perspective of a package run the following command as root: yum history package-list glob_expression… Example 8.22. Tracing the history of a package Syst em Administ rat ors Guide 74

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For example to trace the history of subscription-manager and related packages type the following at a shell prompt: yum history package-list subscription-manager\ Loaded plugins: langpacks product-id search-disabled-repos subscription-manager ID | Actions | Package ---------------------------------------------------------------------- --------- 2 | Updated | subscription-manager-1.13.22-1.el7.x86_64 EE 2 | Update | 1.15.9-15.el7.x86_64 EE 2 | Obsoleted | subscription-manager-firstboot-1.13.22- 1.el7.x86_64 EE 2 | Updated | subscription-manager-gui-1.13.22-1.el7.x86_64 EE 2 | Update | 1.15.9-15.el7.x86_64 EE 2 | Obsoleting | subscription-manager-initial-setup-addon- 1.15.9-15.el7.x86_64 EE 1 | Install | subscription-manager-1.13.22-1.el7.x86_64 1 | Install | subscription-manager-firstboot-1.13.22- 1.el7.x86_64 1 | Install | subscription-manager-gui-1.13.22-1.el7.x86_64 history package-list In this example three packages were installed during the initial system installation: subscription- manager subscription-manager-firstboot and subscription-manager-gui. In the third transaction all these packages were updated from version 1.10.11 to version 1.10.17. 8.4 .2. Examining T ransactions To display the summary of a single transaction as root use the yum history summary command in the following form: yum history summary id Here id stands for the ID of the transaction. To examine a particular transaction or transactions in more detail run the following command as root: yum history info id… The id argument is optional and when you omit it yum automatically uses the last transaction. Note that when specifying more than one transaction you can also use a range: yum history info start_id..end_id Example 8.23. Example output of yum history info The following is sample output for two transactions each installing one new package: ⁠Chapt er 8 . Yum 75

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yum history info 4..5 Loaded plugins: langpacks product-id search-disabled-repos subscription-manager Transaction ID : 4..5 Begin time : Mon Dec 7 16:51:07 2015 Begin rpmdb : 1252:d2b62b7b5768e855723954852fd7e55f641fbad9 End time : 17:18:49 2015 27 minutes End rpmdb : 1253:cf8449dc4c53fc0cbc0a4c48e496a6c50f3d43c5 User : Maxim Svistunov msvistun Return-Code : Success Command Line : install tigervnc-server.x86_64 Command Line : reinstall tigervnc-server Transaction performed with: Installed rpm-4.11.3-17.el7.x86_64 rhel-7- server-rpms Installed subscription-manager-1.15.9-15.el7.x86_64 rhel-7- server-rpms Installed yum-3.4.3-132.el7.noarch rhel-7- server-rpms Packages Altered: Reinstall tigervnc-server-1.3.1-3.el7.x86_64 rhel-7-server-rpms history info You can also view additional information such as what configuration options were used at the time of the transaction or from what repository and why were certain packages installed. To determine what additional information is available for a certain transaction type the following at a shell prompt as root: yum history addon-info id Similarly to yum history info when no id is provided yum automatically uses the latest transaction. Another way to refer to the latest transaction is to use the last keyword: yum history addon-info last Example 8.24 . Example output of yum history addon-info For the fourth transaction in the history the yum history addon-info command provides the following output: yum history addon-info 4 Loaded plugins: langpacks product-id subscription-manager Transaction ID: 4 Available additional history information: config-main config-repos saved_tx history addon-info In the output of the yum history addon-info command three types of information are available: Syst em Administ rat ors Guide 76

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config-main — global yum options that were in use during the transaction. See Section 8.5.1 “Setting main Options” for information on how to change global options. config-repos — options for individual yum repositories. See Section 8.5.2 “Setting repository Options” for information on how to change options for individual repositories. saved_tx — the data that can be used by the yum load-transaction command in order to repeat the transaction on another machine see below. To display a selected type of additional information run the following command as root: yum history addon-info id information 8.4 .3. Reverting and Repeating T ransactions Apart from reviewing the transaction history the yum history command provides means to revert or repeat a selected transaction. To revert a transaction type the following at a shell prompt as root: yum history undo id To repeat a particular transaction as root run the following command: yum history redo id Both commands also accept the last keyword to undo or repeat the latest transaction. Note that both yum history undo and yum history redo commands only revert or repeat the steps that were performed during a transaction. If the transaction installed a new package the yum history undo command will uninstall it and if the transaction uninstalled a package the command will again install it. This command also attempts to downgrade all updated packages to their previous version if these older packages are still available. When managing several identical systems yum also enables you to perform a transaction on one of them store the transaction details in a file and after a period of testing repeat the same transaction on the remaining systems as well. To store the transaction details to a file type the following at a shell prompt as root: yum -q history addon-info id saved_tx file_name Once you copy this file to the target system you can repeat the transaction by using the following command as root: yum load-transaction file_name You can configure load-transaction to ignore missing packages or rpmdb version. For more information on these configuration options see the yum.conf5 man page. 8.4 .4 . Starting New T ransaction History Yum stores the transaction history in a single SQLite database file. To start new transaction history run the following command as root: yum history new ⁠Chapt er 8 . Yum 77

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This will create a new empty database file in the /var/lib/yum/history/ directory. The old transaction history will be kept but will not be accessible as long as a newer database file is present in the directory. 8.5. Configuring Yum and Yum Repositories Note To expand your expertise you might also be interested in the Red Hat System Administration III RH254 and RHCSA Rapid Track RH199 training courses. The configuration information for yum and related utilities is located at /etc/yum.conf. This file contains one mandatory main section which enables you to set yum options that have global effect and can also contain one or more repository sections which allow you to set repository- specific options. However it is recommended to define individual repositories in new or existing .repo files in the /etc/yum.repos.d/ directory. The values you define in individual repository sections of the /etc/yum.conf file override values set in the main section. This section shows you how to: set global yum options by editing the main section of the /etc/yum.conf configuration file set options for individual repositories by editing the repository sections in /etc/yum.conf and .repo files in the /etc/yum.repos.d/ directory use yum variables in /etc/yum.conf and files in the /etc/yum.repos.d/ directory so that dynamic version and architecture values are handled correctly add enable and disable yum repositories on the command line and set up your own custom yum repository. 8.5.1. Setting main Options The /etc/yum.conf configuration file contains exactly one main section and while some of the key-value pairs in this section affect how yum operates others affect how yum treats repositories. You can add many additional options under the main section heading in /etc/yum.conf. A sample /etc/yum.conf configuration file can look like this: main cachedir/var/cache/yum/basearch/releasever keepcache0 debuglevel2 logfile/var/log/yum.log exactarch1 obsoletes1 gpgcheck1 plugins1 installonly_limit3 Syst em Administ rat ors Guide 78

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comments abridged PUT YOUR REPOS HERE OR IN separate files named file.repo in /etc/yum.repos.d The following are the most commonly used options in the main section: assumeyes v a l u e The assumeyes option determines whether or not yum prompts for confirmation of critical actions. Replace value with one of: 0 default — yum prompts for confirmation of critical actions it performs. 1 — Do not prompt for confirmation of critical yum actions. If assumeyes1 is set yum behaves in the same way as the command-line options -y and --assumeyes. cachedir d i r e c t o r y Use this option to set the directory where yum stores its cache and database files. Replace directory with an absolute path to the directory. By default yums cache directory is /var/cache/yum/basearch/releasever/. See Section 8.5.3 “Using Yum Variables” for descriptions of the basearch and releasever yum variables. debuglevel v a l u e This option specifies the detail of debugging output produced by yum. Here value is an integer between 1 and 10. Setting a higher debuglevel value causes yum to display more detailed debugging output. debuglevel2 is the default while debuglevel0 disables debugging output. exactarch v a l u e With this option you can set yum to consider the exact architecture when updating already installed packages. Replace value with: 0 — Do not take into account the exact architecture when updating packages. 1 default — Consider the exact architecture when updating packages. With this setting yum does not install a package for 32-bit architecture to update a package already installed on the system with 64-bit architecture. exclude p a c k a g e _ n a m e m o r e _ p a c k a g e _ n a m e s The exclude option enables you to exclude packages by keyword during installation or system update. Listing multiple packages for exclusion can be accomplished by quoting a space-delimited list of packages. Shell glob expressions using wildcards for example and are allowed. gpgcheck v a l u e Use the gpgcheck option to specify if yum should perform a GPG signature check on packages. Replace value with: 0 — Disable GPG signature-checking on packages in all repositories including local package installation. ⁠Chapt er 8 . Yum 79

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1 default — Enable GPG signature-checking on all packages in all repositories including local package installation. With gpgcheck enabled all packages signatures are checked. If this option is set in the main section of the /etc/yum.conf file it sets the GPG- checking rule for all repositories. However you can also set gpgcheckvalue for individual repositories instead that is you can enable GPG-checking on one repository while disabling it on another. Setting gpgcheckvalue for an individual repository in its corresponding .repo file overrides the default if it is present in /etc/yum.conf. For more information on GPG signature-checking see Section A.3.2 “Checking Package Signatures”. group_command v a l u e Use the group_command option to specify how the yum group install yum group upgrade and yum group remove commands handle a package group. Replace value with on of: simple — Install all members of a package group. Upgrade only previously installed packages but do not install packages that have been added to the group in the meantime. compat — Similar to simple but yum upgrade also installs packages that were added to the group since the previous upgrade. objects — default. With this option yum keeps track of the previously installed groups and distinguishes between packages installed as a part of the group and packages installed separately. See Example 8.15 “Viewing information on the LibreOffice package group” group_package_types p a c k a g e _ t y p e m o r e _ p a c k a g e _ t y p e s Here you can specify which type of packages optional default or mandatory is installed when the yum group install command is called. The default and mandatory package types are chosen by default. history_record v a l u e With this option you can set yum to record transaction history. Replace value with one of: 0 — yum should not record history entries for transactions. 1 default — yum should record history entries for transactions. This operation takes certain amount of disk space and some extra time in the transactions but it provides a lot of information about past operations which can be displayed with the yum history command. history_record1 is the default. For more information on the yum history command see Section 8.4 “Working with Transaction History”. Note Yum uses history records to detect modifications to the rpmdb data base that have been done outside of yum. In such case yum displays a warning and automatically searches for possible problems caused by altering rpmdb. With history_record turned off yum is not able to detect these changes and no automatic checks are performed. Syst em Administ rat ors Guide 80

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installonlypkgs s p a c e s e p a r a t e d l i s t o f p a c k a g e s Here you can provide a space-separated list of packages which yum can install but will never update. See the yum.conf5 manual page for the list of packages which are install- only by default. If you add the installonlypkgs directive to /etc/yum.conf you should ensure that you list all of the packages that should be install-only including any of those listed under the installonlypkgs section of yum.conf5. In particular kernel packages should always be listed in installonlypkgs as they are by default and installonly_limit should always be set to a value greater than 2 so that a backup kernel is always available in case the default one fails to boot. ⁠installonly_limit v a l u e This option sets how many packages listed in the installonlypkgs directive can be installed at the same time. Replace value with an integer representing the maximum number of versions that can be installed simultaneously for any single package listed in installonlypkgs. The defaults for the installonlypkgs directive include several different kernel packages so be aware that changing the value of installonly_limit also affects the maximum number of installed versions of any single kernel package. The default value listed in /etc/yum.conf is installonly_limit3 and it is not recommended to decrease this value particularly below 2. keepcache v a l u e The keepcache option determines whether yum keeps the cache of headers and packages after successful installation. Here value is one of: 0 default — Do not retain the cache of headers and packages after a successful installation. 1 — Retain the cache after a successful installation. logfile f i l e _ n a m e To specify the location for logging output replace file_name with an absolute path to the file in which yum should write its logging output. By default yum logs to /var/log/yum.log. max_connenctions n u m b e r Here value stands for the maximum number of simultaneous connections default is 5. multilib_policy v a l u e The multilib_policy option sets the installation behavior if several architecture versions are available for package install. Here value stands for: best — install the best-choice architecture for this system. For example setting multilib_policybest on an AMD64 system causes yum to install the 64-bit versions of all packages. all — always install every possible architecture for every package. For example with multilib_policy set to all on an AMD64 system yum would install both the i686 and AMD64 versions of a package if both were available. obsoletes v a l u e ⁠Chapt er 8 . Yum 81

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The obsoletes option enables the obsoletes process logic during updates.When one package declares in its spec file that it obsoletes another package the latter package is replaced by the former package when the former package is installed. Obsoletes are declared for example when a package is renamed. Replace value with one of: 0 — Disable yums obsoletes processing logic when performing updates. 1 default — Enable yums obsoletes processing logic when performing updates. plugins v a l u e This is a global switch to enable or disable yum plug-ins value is one of: 0 — Disable all yum plug-ins globally. Important Disabling all plug-ins is not advised because certain plug-ins provide important yum services. In particular product-id and subscription-manager plug-ins provide support for the certificate-based Content Delivery Network CDN. Disabling plug-ins globally is provided as a convenience option and is generally only recommended when diagnosing a potential problem with yum. 1 default — Enable all yum plug-ins globally. With plugins1 you can still disable a specific yum plug-in by setting enabled0 in that plug-ins configuration file. For more information about various yum plug-ins see Section 8.6 “Yum Plug-ins”. For further information on controlling plug-ins see Section 8.6.1 “Enabling Configuring and Disabling Yum Plug-ins”. reposdir d i r e c t o r y Here directory is an absolute path to the directory where .repo files are located. All .repo files contain repository information similar to the repository sections of /etc/yum.conf. Yum collects all repository information from .repo files and the repository section of the /etc/yum.conf file to create a master list of repositories to use for transactions. If reposdir is not set yum uses the default directory /etc/yum.repos.d/. retries v a l u e This option sets the number of times yum should attempt to retrieve a file before returning an error. value is an integer 0 or greater. Setting value to 0 makes yum retry forever. The default value is 10. For a complete list of available main options see the main OPTIONS section of the yum.conf5 manual page. 8.5.2. Setting repository Options The repository sections where repository is a unique repository ID such as my_personal_repo spaces are not permitted allow you to define individual yum repositories. To avoid conflicts custom repositories should not use names used by Red Hat repositories. The following is a bare minimum example of the form a repository section takes: Syst em Administ rat ors Guide 82

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repository namerepository_name baseurlrepository_url Every repository section must contain the following directives: name r e p o s i t o r y _ n a m e Here repository_name is a human-readable string describing the repository. baseurl r e p o s i t o r y _ u r l Replace repository_url with a URL to the directory where the repodata directory of a repository is located: If the repository is available over HTTP use: http://path/to/repo If the repository is available over FTP use: ftp://path/to/repo If the repository is local to the machine use: file:///path/to/local/repo If a specific online repository requires basic HTTP authentication you can specify your user name and password by prepending it to the URL as username:passwordlink. For example if a repository on http://www.example.com/repo/ requires a username of “user” and a password of “password” then the baseurl link could be specified as http://user:passwordwww.example.com/repo/. Usually this URL is an HTTP link such as: baseurlhttp://path/to/repo/releases/releasever/server/basearch/ os/ Note that yum always expands the releasever arch and basearch variables in URLs. For more information about yum variables see Section 8.5.3 “Using Yum Variables”. Other useful repository directive are: enabled v a l u e This is a simple way to tell yum to use or ignore a particular repository value is one of: 0 — Do not include this repository as a package source when performing updates and installs. This is an easy way of quickly turning repositories on and off which is useful when you desire a single package from a repository that you do not want to enable for updates or installs. 1 — Include this repository as a package source. Turning repositories on and off can also be performed by passing either the -- enablereporepo_name or --disablereporepo_name option to yum or through the Add/Remove Software window of the PackageKit utility. async v a l u e Controls parallel downloading of repository packages. Here value is one of: auto default — parallel downloading is used if possible which means that yum automatically disables it for repositories created by plug-ins to avoid failures. ⁠Chapt er 8 . Yum 83

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on — parallel downloading is enabled for the repository. off — parallel downloading is disabled for the repository. Many more repository options exist part of them have the same form and function as certain main options. For a complete list see the repository OPTIONS section of the yum.conf5 manual page. Example 8.25. A sample /etc/yum.repos.d/redhat.repo file The following is a sample /etc/yum.repos.d/redhat.repo file: Red Hat Repositories Managed by rhsm subscription-manager red-hat-enterprise-linux-scalable-file-system-for-rhel-6-entitlement- rpms name Red Hat Enterprise Linux Scalable File System for RHEL 6 Entitlement RPMs baseurl https://cdn.redhat.com/content/dist/rhel/entitlement- 6/releases/releasever/basearch/scalablefilesystem/os enabled 1 gpgcheck 1 gpgkey file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release sslverify 1 sslcacert /etc/rhsm/ca/redhat-uep.pem sslclientkey /etc/pki/entitlement/key.pem sslclientcert /etc/pki/entitlement/11300387955690106.pem red-hat-enterprise-linux-scalable-file-system-for-rhel-6-entitlement- source-rpms name Red Hat Enterprise Linux Scalable File System for RHEL 6 Entitlement Source RPMs baseurl https://cdn.redhat.com/content/dist/rhel/entitlement- 6/releases/releasever/basearch/scalablefilesystem/source/SRPMS enabled 0 gpgcheck 1 gpgkey file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release sslverify 1 sslcacert /etc/rhsm/ca/redhat-uep.pem sslclientkey /etc/pki/entitlement/key.pem sslclientcert /etc/pki/entitlement/11300387955690106.pem red-hat-enterprise-linux-scalable-file-system-for-rhel-6-entitlement- debug-rpms name Red Hat Enterprise Linux Scalable File System for RHEL 6 Entitlement Debug RPMs baseurl https://cdn.redhat.com/content/dist/rhel/entitlement- 6/releases/releasever/basearch/scalablefilesystem/debug enabled 0 gpgcheck 1 gpgkey file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release Syst em Administ rat ors Guide 84

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sslverify 1 sslcacert /etc/rhsm/ca/redhat-uep.pem sslclientkey /etc/pki/entitlement/key.pem sslclientcert /etc/pki/entitlement/11300387955690106.pem 8.5.3. Using Yum Variables You can use and reference the following built-in variables in yum commands and in all yum configuration files that is /etc/yum.conf and all .repo files in the /etc/yum.repos.d/ directory: releasever You can use this variable to reference the release version of Red Hat Enterprise Linux. Yum obtains the value of releasever from the distroverpkgvalue line in the /etc/yum.conf configuration file. If there is no such line in /etc/yum.conf then yum infers the correct value by deriving the version number from the redhat-releaseproduct package that provides the redhat-release file. arch You can use this variable to refer to the systems CPU architecture as returned when calling Pythons os.uname function. Valid values for arch include: i586 i686 and x86_64. basearch You can use basearch to reference the base architecture of the system. For example i686 and i586 machines both have a base architecture of i386 and AMD64 and Intel64 machines have a base architecture of x86_64. YUM0-9 These ten variables are each replaced with the value of any shell environment variables with the same name. If one of these variables is referenced in /etc/yum.conf for example and a shell environment variable with the same name does not exist then the configuration file variable is not replaced. To define a custom variable or to override the value of an existing one create a file with the same name as the variable without the “” sign in the /etc/yum/vars/ directory and add the desired value on its first line. For example repository descriptions often include the operating system name. To define a new variable called osname create a new file with “Red Hat Enterprise Linux” on the first line and save it as /etc/yum/vars/osname: echo "Red Hat Enterprise Linux 7" /etc/yum/vars/osname Instead of “Red Hat Enterprise Linux 7” you can now use the following in the .repo files: nameosname releasever 8.5.4 . Viewing the Current Configuration ⁠Chapt er 8 . Yum 85

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To display the current values of global yum options that is the options specified in the main section of the /etc/yum.conf file execute the yum-config-manager command with no command-line options: yum-config-manager To list the content of a different configuration section or sections use the command in the following form: yum-config-manager section… You can also use a glob expression to display the configuration of all matching sections: yum-config-manager glob_expression… Example 8.26 . Viewing configuration of the main section To list all configuration options and their corresponding values for the main section type the following at a shell prompt: yum-config-manager main \ Loaded plugins: langpacks product-id subscription-manager main main alwaysprompt True assumeyes False bandwith 0 bugtracker_url https://bugzilla.redhat.com/enter_bug.cgi productRed20Hat20Enterprise20Linux206componentyum cache 0 output truncated 8.5.5. Adding Enabling and Disabling a Yum Repository Note To expand your expertise you might also be interested in the Red Hat System Administration III RH254 training course. Section 8.5.2 “Setting repository Options” describes various options you can use to define a yum repository. This section explains how to add enable and disable a repository by using the yum- config-manager command. Syst em Administ rat ors Guide 86

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Important When the system is registered with Red Hat Subscription Management to the certificate-based Content Delivery Network CDN the Red Hat Subscription Manager tools are used to manage repositories in the /etc/yum.repos.d/redhat.repo file. Adding a Yum Repo sit o ry To define a new repository you can either add a repository section to the /etc/yum.conf file or to a .repo file in the /etc/yum.repos.d/ directory. All files with the .repo file extension in this directory are read by yum and it is recommended to define your repositories here instead of in /etc/yum.conf. Warning Obtaining and installing software packages from unverified or untrusted software sources other than Red Hats certificate-based Content Delivery Network CDN constitutes a potential security risk and could lead to security stability compatibility and maintainability issues. Yum repositories commonly provide their own .repo file. To add such a repository to your system and enable it run the following command as root: yum-config-manager --add-repo repository_url …where repository_url is a link to the .repo file. Example 8.27. Adding example.repo To add a repository located at http://www.example.com/example.repo type the following at a shell prompt: yum-config-manager --add-repo http://www.example.com/example.repo Loaded plugins: langpacks product-id subscription-manager adding repo from: http://www.example.com/example.repo grabbing file http://www.example.com/example.repo to /etc/yum.repos.d/example.repo example.repo | 413 B 00:00 repo saved to /etc/yum.repos.d/example.repo Enabling a Yum Repo sit o ry To enable a particular repository or repositories type the following at a shell prompt as root: yum-config-manager --enable repository… ⁠Chapt er 8 . Yum 87

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…where repository is the unique repository ID use yum repolist all to list available repository IDs. Alternatively you can use a glob expression to enable all matching repositories: yum-config-manager --enable glob_expression… Example 8.28. Enabling repositories defined in custom sections of /etc/yum.conf. To enable repositories defined in the example example-debuginfo and example- sourcesections type: yum-config-manager --enable example\ Loaded plugins: langpacks product-id subscription-manager repo: example example bandwidth 0 base_persistdir /var/lib/yum/repos/x86_64/7Server baseurl http://www.example.com/repo/7Server/x86_64/ cache 0 cachedir /var/cache/yum/x86_64/7Server/example output truncated Example 8.29 . Enabling all repositories To enable all repositories defined both in the /etc/yum.conf file and in the /etc/yum.repos.d/ directory type: yum-config-manager --enable \ Loaded plugins: langpacks product-id subscription-manager repo: example example bandwidth 0 base_persistdir /var/lib/yum/repos/x86_64/7Server baseurl http://www.example.com/repo/7Server/x86_64/ cache 0 cachedir /var/cache/yum/x86_64/7Server/example output truncated When successful the yum-config-manager --enable command displays the current repository configuration. Disabling a Yum Repo sit o ry To disable a yum repository run the following command as root: yum-config-manager --disable repository… …where repository is the unique repository ID use yum repolist all to list available repository IDs. Similarly to yum-config-manager --enable you can use a glob expression to disable all matching repositories at the same time: Syst em Administ rat ors Guide 88

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yum-config-manager --disable glob_expression… Example 8.30. Disabling all repositories To disable all repositories defined both in the /etc/yum.conf file and in the /etc/yum.repos.d/ directory type: yum-config-manager --disable \ Loaded plugins: langpacks product-id subscription-manager repo: example example bandwidth 0 base_persistdir /var/lib/yum/repos/x86_64/7Server baseurl http://www.example.com/repo/7Server/x86_64/ cache 0 cachedir /var/cache/yum/x86_64/7Server/example output truncated When successful the yum-config-manager --disable command displays the current configuration. 8.5.6. Creating a Yum Repository To set up a yum repository follow these steps: 1. Install the createrepo package. To do so type the following at a shell prompt as root: yum install createrepo 2. Copy all packages that you want to have in your repository into one directory such as /mnt/local_repo/. 3. Change to this directory and run the following command: createrepo --database /mnt/local_repo This creates the necessary metadata for your yum repository as well as the sqlite database for speeding up yum operations. 8.5.7. Adding the Optional and Supplementary Repositories The Optional and Supplementary subscription channels provide additional software packages for Red Hat Enterprise Linux that cover open source licensed software in the Optional channel and proprietary licensed software in the Supplementary channel. Before subscribing to the Optional and Supplementary channels see the Scope of Coverage Details. If you decide to install packages from these channels follow the steps documented in the article called How to access Optional and Supplementary channels and -devel packages using Red Hat Subscription Manager RHSM on the Red Hat Customer Portal. 8.6. Yum Plug-ins ⁠Chapt er 8 . Yum 89

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8.6. Yum Plug-ins Yum provides plug-ins that extend and enhance its operations. Certain plug-ins are installed by default. Yum always informs you which plug-ins if any are loaded and active whenever you call any yum command. For example: yum info yum Loaded plugins: langpacks product-id subscription-manager output truncated Note that the plug-in names which follow Loaded plugins are the names you can provide to the - -disablepluginplugin_name option. 8.6.1. Enabling Configuring and Disabling Yum Plug-ins To enable yum plug-ins ensure that a line beginning with plugins is present in the main section of /etc/yum.conf and that its value is 1: plugins1 You can disable all plug-ins by changing this line to plugins0. Important Disabling all plug-ins is not advised because certain plug-ins provide important yum services. In particular the product-id and subscription-manager plug-ins provide support for the certificate-based Content Delivery Network CDN. Disabling plug-ins globally is provided as a convenience option and is generally only recommended when diagnosing a potential problem with yum. Every installed plug-in has its own configuration file in the /etc/yum/pluginconf.d/ directory. You can set plug-in specific options in these files. For example here is the aliases plug-ins aliases.conf configuration file: main enabled1 Similar to the /etc/yum.conf file the plug-in configuration files always contain a main section where the enabled option controls whether the plug-in is enabled when you run yum commands. If this option is missing you can add it manually to the file. If you disable all plug-ins by setting enabled0 in /etc/yum.conf then all plug-ins are disabled regardless of whether they are enabled in their individual configuration files. If you merely want to disable all yum plug-ins for a single yum command use the --noplugins option. If you want to disable one or more yum plug-ins for a single yum command add the -- disablepluginplugin_name option to the command. For example to disable the aliases plug- in while updating a system type: yum update --disablepluginaliases Syst em Administ rat ors Guide 90

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The plug-in names you provide to the --disableplugin option are the same names listed after the Loaded plugins line in the output of any yum command. You can disable multiple plug-ins by separating their names with commas. In addition you can match multiple plug-in names or shorten long ones by using glob expressions: yum update --disablepluginaliaseslang 8.6.2. Installing Additional Yum Plug-ins Yum plug-ins usually adhere to the yum-plugin-plugin_name package-naming convention but not always: the package which provides the kabi plug-in is named kabi-yum-plugins for example. You can install a yum plug-in in the same way you install other packages. For instance to install the yum-aliases plug-in type the following at a shell prompt: yum install yum-plugin-aliases 8.6.3. Working with Yum Plug-ins The following list provides descriptions and usage instructions for several useful yum plug-ins. Plug- ins are listed by names brackets contain the name of the package. search-disabled-repos s u b s c r i p t i o n - m a n a g e r The search-disabled-repos plug-in allows you to temporarily or permanently enable disabled repositories to help resolve dependencies. With this plug-in enabled when Yum fails to install a package due to failed dependency resolution it offers to temporarily enable disabled repositories and try again. If the installation succeeds Yum also offers to enable the used repositories permanently. Note that the plug-in works only with the repositories that are managed by subscription-manager and not with custom repositories. Important If yum is executed with the --assumeyes or -y option or if the assumeyes directive is enabled in /etc/yum.conf the plug-in enables disabled repositories both temporarily and permanently without prompting for confirmation. This may lead to problems for example enabling repositories that you do not want enabled. To configure the search-disabled-repos plug-in edit the configuration file located in /etc/yum/pluginconf.d/search-disabled-repos.conf. For the list of directives you can use in the main section see the table below. Table 8.3. Supported search-disabled-repos.conf directives Directive Description enabledvalue Allows you to enable or disable the plug-in. The value must be either 1 enabled or 0 disabled. The plug-in is enabled by default. notify_onlyvalue Allows you to restrict the behavior of the plug-in to notifications only. The value must be either 1 notify only without modifying the behavior of Yum or 0 modify the behavior of Yum. By default the plug-in only notifies the user. ⁠Chapt er 8 . Yum 91

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ignored_reposreposit ories Allows you to specify the repositories that will not be enabled by the plug-in. Directive Description kabi k a b i - y u m - p l u g i n s The kabi plug-in checks whether a driver update package conforms with the official Red Hat kernel Application Binary Interface kABI. With this plug-in enabled when a user attempts to install a package that uses kernel symbols which are not on a whitelist a warning message is written to the system log. Additionally configuring the plug-in to run in enforcing mode prevents such packages from being installed at all. To configure the kabi plug-in edit the configuration file located in /etc/yum/pluginconf.d/kabi.conf. A list of directives that can be used in the main section is shown in the table below. Table 8.4 . Supported kabi.conf directives Directive Description enabledvalue Allows you to enable or disable the plug-in. The value must be either 1 enabled or 0 disabled. When installed the plug-in is enabled by default. whitelistsdirectory Allows you to specify the directory in which the files with supported kernel symbols are located. By default the kabi plug-in uses files provided by the kernel-abi-whitelists package that is the /usr/lib/modules/kabi-rhel70/ directory. enforcevalue Allows you to enable or disable enforcing mode. The value must be either 1 enabled or 0 disabled. By default this option is commented out and the kabi plug-in only displays a warning message. product-id s u b s c r i p t i o n - m a n a g e r The product-id plug-in manages product identity certificates for products installed from the Content Delivery Network. The product-id plug-in is installed by default. langpacks y u m - l a n g p a c k s The langpacks plug-in is used to search for locale packages of a selected language for every package that is installed. The langpacks plug-in is installed by default. aliases y u m - p l u g i n - a l i a s e s The aliases plug-in adds the alias command-line option which enables configuring and using aliases for yum commands. yum-changelog y u m - p l u g i n - c h a n g e l o g The yum-changelog plug-in adds the --changelog command-line option that enables viewing package change logs before and after updating. yum-tmprepo y u m - p l u g i n - t m p r e p o The yum-tmprepo plug-in adds the --tmprepo command-line option that takes the URL of a repository file downloads and enables it for only one transaction. This plug-in tries to ensure the safe temporary usage of repositories. By default it does not allow to disable the gpg check. yum-verify y u m - p l u g i n - v e r i f y Syst em Administ rat ors Guide 92

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The yum-verify plug-in adds the verify verify-rpm and verify-all command-line options for viewing verification data on the system. yum-versionlock y u m - p l u g i n - v e r s i o n l o c k The yum-versionlock plug-in excludes other versions of selected packages which enables protecting packages from being updated by newer versions. With the versionlock command-line option you can view and edit the list of locked packages. 8.7. Additional Resources For more information on how to manage software packages on Red Hat Enterprise Linux see the resources listed below. Installed Documentation yum8 — The manual page for the yum command-line utility provides a complete list of supported options and commands. yumdb8 — The manual page for the yumdb command-line utility documents how to use this tool to query and if necessary alter the yum database. yum.conf5 — The manual page named yum.conf documents available yum configuration options. yum-utils1 — The manual page named yum-utils lists and briefly describes additional utilities for managing yum configuration manipulating repositories and working with yum database. Online Resources Yum Guides — The Yum Guides page on the project home page provides links to further documentation. Red Hat Access Labs — The Red Hat Access Labs includes a “Yum Repository Configuration Helper”. See Also Chapter 5 Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands. Appendix A RPM describes the RPM Package Manager RPM the packaging system used by Red Hat Enterprise Linux. ⁠Chapt er 8 . Yum 93

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⁠Part IV. Infrastructure Services This part provides information on how to configure services and daemons and enable remote access to a Red Hat Enterprise Linux machine. Syst em Administ rat ors Guide 94

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Chapter 9. Managing Services with systemd 9.1. Introduction to systemd Systemd is a system and service manager for Linux operating systems. It is designed to be backwards compatible with SysV init scripts and provides a number of features such as parallel startup of system services at boot time on-demand activation of daemons support for system state snapshots or dependency-based service control logic. In Red Hat Enterprise Linux 7 systemd replaces Upstart as the default init system. Systemd introduces the concept of systemd units. These units are represented by unit configuration files located in one of the directories listed in Table 9.2 “Systemd Unit Files Locations” and encapsulate information about system services listening sockets saved system state snapshots and other objects that are relevant to the init system. For a complete list of available systemd unit types see Table 9.1 “Available systemd Unit Types”. Table 9 .1. Available systemd Unit Types Unit Type File Extension Description Service unit .service A system service. Target unit .target A group of systemd units. Automount unit .automount A file system automount point. Device unit .device A device file recognized by the kernel. Mount unit .mount A file system mount point. Path unit .path A file or directory in a file system. Scope unit .scope An externally created process. Slice unit .slice A group of hierarchically organized units that manage system processes. Snapshot unit .snapshot A saved state of the systemd manager. Socket unit .socket An inter-process communication socket. Swap unit .swap A swap device or a swap file. Timer unit .timer A systemd timer. Table 9 .2. Systemd Unit Files Locations Directory Description /usr/lib/systemd/system/ Systemd unit files distributed with installed RPM packages. /run/systemd/system/ Systemd unit files created at run time. This directory takes precedence over the directory with installed service unit files. /etc/systemd/system/ Systemd unit files created by systemctl enable as well as unit files added for extending a service. This directory takes precedence over the directory with runtime unit files. 9.1.1. Main Features In Red Hat Enterprise Linux 7 the systemd system and service manager provides the following main features: Socket-based activation — At boot time systemd creates listening sockets for all system services that support this type of activation and passes the sockets to these services as soon as they are started. This not only allows systemd to start services in parallel but also makes it possible to ⁠Chapt er 9 . Managing Services wit h syst emd 95

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restart a service without losing any message sent to it while it is unavailable: the corresponding socket remains accessible and all messages are queued. Systemd uses socket units for socket-based activation. Bus-based activation — System services that use D-Bus for inter-process communication can be started on-demand the first time a client application attempts to communicate with them. Systemd uses D-Bus service files for bus-based activation. Device-based activation — System services that support device-based activation can be started on- demand when a particular type of hardware is plugged in or becomes available. Systemd uses device units for device-based activation. Path-based activation — System services that support path-based activation can be started on- demand when a particular file or directory changes its state. Systemd uses path units for path- based activation. System state snapshots — Systemd can temporarily save the current state of all units or restore a previous state of the system from a dynamically created snapshot. To store the current state of the system systemd uses dynamically created snapshot units. Mount and automount point management — Systemd monitors and manages mount and automount points. Systemd uses mount units for mount points and automount units for automount points. Aggressive parallelization — Because of the use of socket-based activation systemd can start system services in parallel as soon as all listening sockets are in place. In combination with system services that support on-demand activation parallel activation significantly reduces the time required to boot the system. Transactional unit activation logic — Before activating or deactivating a unit systemd calculates its dependencies creates a temporary transaction and verifies that this transaction is consistent. If a transaction is inconsistent systemd automatically attempts to correct it and remove non-essential jobs from it before reporting an error. Backwards compatibility with SysV init — Systemd supports SysV init scripts as described in the Linux Standard Base Core Specification which eases the upgrade path to systemd service units. 9.1.2. Compatibility Changes The systemd system and service manager is designed to be mostly compatible with SysV init and Upstart. The following are the most notable compatibility changes with regards to the previous major release of the Red Hat Enterprise Linux system: Systemd has only limited support for runlevels. It provides a number of target units that can be directly mapped to these runlevels and for compatibility reasons it is also distributed with the earlier runlevel command. Not all systemd targets can be directly mapped to runlevels however and as a consequence this command might return N to indicate an unknown runlevel. It is recommended that you avoid using the runlevel command if possible. For more information about systemd targets and their comparison with runlevels see Section 9.3 “Working with systemd Targets”. The systemctl utility does not support custom commands. In addition to standard commands such as start stop and status authors of SysV init scripts could implement support for any number of arbitrary commands in order to provide additional functionality. For example the init script for iptables in Red Hat Enterprise Linux 6 could be executed with the panic command Syst em Administ rat ors Guide 96

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which immediately enabled panic mode and reconfigured the system to start dropping all incoming and outgoing packets. This is not supported in systemd and the systemctl only accepts documented commands. For more information about the systemctl utility and its comparison with the earlier service utility see Section 9.2 “Managing System Services”. The systemctl utility does not communicate with services that have not been started by systemd. When systemd starts a system service it stores the ID of its main process in order to keep track of it. The systemctl utility then uses this PID to query and manage the service. Consequently if a user starts a particular daemon directly on the command line systemctl is unable to determine its current status or stop it. Systemd stops only running services. Previously when the shutdown sequence was initiated Red Hat Enterprise Linux 6 and earlier releases of the system used symbolic links located in the /etc/rc0.d/ directory to stop all available system services regardless of their status. With systemd only running services are stopped on shutdown. System services are unable to read from the standard input stream. When systemd starts a service it connects its standard input to /dev/null to prevent any interaction with the user. System services do not inherit any context such as the HOME and PATH environment variables from the invoking user and their session. Each service runs in a clean execution context. When loading a SysV init script systemd reads dependency information encoded in the Linux Standard Base LSB header and interprets it at run time. All operations on service units are subject to a default timeout of 5 minutes to prevent a malfunctioning service from freezing the system. This value is hardcoded for services that are generated from initscripts and cannot be changed. However individual configuration files can be used to specify a longer timeout value per service see Example 9.21 “Changing the timeout limit” For a detailed list of compatibility changes introduced with systemd see the Migration Planning Guide for Red Hat Enterprise Linux 7. 9.2. Managing System Services Note To expand your expertise you might also be interested in the Red Hat System Administration II RH134 training course. Previous versions of Red Hat Enterprise Linux which were distributed with SysV init or Upstart used init scripts located in the /etc/rc.d/init.d/ directory. These init scripts were typically written in Bash and allowed the system administrator to control the state of services and daemons in their system. In Red Hat Enterprise Linux 7 these init scripts have been replaced with service units. Service units end with the .service file extension and serve a similar purpose as init scripts. To view start stop restart enable or disable system services use the systemctl command as described in Table 9.3 “Comparison of the service Utility with systemctl ” Table 9.4 “Comparison of the chkconfig Utility with systemctl” and further in this section. The service and chkconfig commands are still available in the system and work as expected but are only included for compatibility reasons and should be avoided. Table 9 .3. Comparison of the service Utility with systemctl ⁠Chapt er 9 . Managing Services wit h syst emd 97

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service systemctl Description service name start systemctl start name.service Starts a service. service name stop systemctl stop name.service Stops a service. service name restart systemctl restart name.service Restarts a service. service name condrestart systemctl try-restart name.service Restarts a service only if it is running. service name reload systemctl reload name.service Reloads configuration. service name status systemctl status name.service systemctl is-active name.service Checks if a service is running. service --status-all systemctl list-units --type service --all Displays the status of all services. Table 9 .4 . Comparison of the chkconfig Utility with systemctl chkconfig systemctl Description chkconfig name on systemctl enable name.service Enables a service. chkconfig name off systemctl disable name.service Disables a service. chkconfig --list name systemctl status name.service systemctl is-enabled name.service Checks if a service is enabled. chkconfig --list systemctl list-unit-files --type service Lists all services and checks if they are enabled. chkconfig --list systemctl list-dependencies -- after Lists services that are ordered to start before the specified unit. chkconfig --list systemctl list-dependencies -- before Lists services that are ordered to start after the specified unit. Specifying Service Unit s For clarity all command examples in the rest of this section use full unit names with the .service file extension for example: systemctl stop nfs-server.service However the file extension can be omitted in which case the systemctl utility assumes the argument is a service unit. The following command is equivalent to the one above: systemctl stop nfs-server Additionally some units have alias names. Those names can have shorter names than units which can be used instead of the actual unit names. To find all aliases that can be used for a particular unit use: systemctl show nfs-server.service -p Names Syst em Administ rat ors Guide 98

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Behavio r o f systemctl in a chroot Enviro nment If you change the root directory using the chroot command most systemctl commands refuse to perform any action. The reason for this is that the systemd process and the user that used the chroot command do not have the same view of the filesystem. This happens for example when systemctl is invoked from a kickstart file. The exception to this are unit file commands such as the systemctl enable and systemctl disable commands. These commands do not need a running system and do not affect running processes but they do affect unit files. Therefore you can run these commands even in chroot environment. For example to enable the httpd service on a system under the /srv/website1/ directory: chroot /srv/website1 systemctl enable httpd.service Created symlink /etc/systemd/system/multi- user.target.wants/httpd.service pointing to /usr/lib/systemd/system/httpd.service. 9.2.1. Listing Services To list all currently loaded service units type the following at a shell prompt: systemctl list-units --type service For each service unit file this command displays its full name UNIT followed by a note whether the unit file has been loaded LOAD its high-level ACTIVE and low-level SUB unit file activation state and a short description DESCRIPTION. By default the systemctl list-units command displays only active units. If you want to list all loaded units regardless of their state run this command with the --all or -a command line option: systemctl list-units --type service --all You can also list all available service units to see if they are enabled. To do so type: systemctl list-unit-files --type service For each service unit this command displays its full name UNIT FILE followed by information whether the service unit is enabled or not STATE. For information on how to determine the status of individual service units see Section 9.2.2 “Displaying Service Status”. Example 9 .1. Listing Services To list all currently loaded service units run the following command: systemctl list-units --type service UNIT LOAD ACTIVE SUB DESCRIPTION abrt-ccpp.service loaded active exited Install ABRT coredump hook abrt-oops.service loaded active running ABRT kernel log watcher abrt-vmcore.service loaded active exited Harvest vmcores ⁠Chapt er 9 . Managing Services wit h syst emd 99

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for ABRT abrt-xorg.service loaded active running ABRT Xorg log watcher abrtd.service loaded active running ABRT Automated Bug Reporting Tool ... systemd-vconsole-setup.service loaded active exited Setup Virtual Console tog-pegasus.service loaded active running OpenPegasus CIM Server LOAD Reflects whether the unit definition was properly loaded. ACTIVE The high-level unit activation state i.e. generalization of SUB. SUB The low-level unit activation state values depend on unit type. 46 loaded units listed. Pass --all to see loaded but inactive units too. To show all installed unit files use systemctl list-unit-files To list all installed service unit files to determine if they are enabled type: systemctl list-unit-files --type service UNIT FILE STATE abrt-ccpp.service enabled abrt-oops.service enabled abrt-vmcore.service enabled abrt-xorg.service enabled abrtd.service enabled ... wpa_supplicant.service disabled ypbind.service disabled 208 unit files listed. 9.2.2. Displaying Service Status To display detailed information about a service unit that corresponds to a system service type the following at a shell prompt: systemctl status name.service Replace name with the name of the service unit you want to inspect for example gdm. This command displays the name of the selected service unit followed by its short description one or more fields described in Table 9.5 “Available Service Unit Information” and if it is executed by the root user also the most recent log entries. Table 9 .5. Available Service Unit Information Field Description Loaded Information whether the service unit has been loaded the absolute path to the unit file and a note whether the unit is enabled. Syst em Administ rat ors Guide 100

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Active Information whether the service unit is running followed by a time stamp. Main PID The PID of the corresponding system service followed by its name. Status Additional information about the corresponding system service. Process Additional information about related processes. CGroup Additional information about related Control Groups cgroups. Field Description To only verify that a particular service unit is running run the following command: systemctl is-active name.service Similarly to determine whether a particular service unit is enabled type: systemctl is-enabled name.service Note that both systemctl is-active and systemctl is-enabled return an exit status of 0 if the specified service unit is running or enabled. For information on how to list all currently loaded service units see Section 9.2.1 “Listing Services”. Example 9 .2. Displaying Service Status The service unit for the GNOME Display Manager is named gdm.service. To determine the current status of this service unit type the following at a shell prompt: systemctl status gdm.service gdm.service - GNOME Display Manager Loaded: loaded /usr/lib/systemd/system/gdm.service enabled Active: active running since Thu 2013-10-17 17:31:23 CEST 5min ago Main PID: 1029 gdm CGroup: /system.slice/gdm.service ├─1029 /usr/sbin/gdm ├─1037 /usr/libexec/gdm-simple-slave --display-id /org/gno... └─1047 /usr/bin/Xorg :0 -background none -verbose -auth /r... Oct 17 17:31:23 localhost systemd1: Started GNOME Display Manager. Example 9 .3. Displaying Services Ordered to Start Before a Service To determine what services are ordered to start before the specified service type the following at a shell prompt: systemctl list-dependencies --after gdm.service gdm.service ├─dbus.socket ├─gettytty1.service ├─livesys.service ├─plymouth-quit.service ├─system.slice ⁠Chapt er 9 . Managing Services wit h syst emd 101

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├─systemd-journald.socket ├─systemd-user-sessions.service └─basic.target output truncated Example 9 .4 . Displaying Services Ordered to Start After a Service To determine what services are ordered to start after the specified service type the following at a shell prompt: systemctl list-dependencies --before gdm.service gdm.service ├─dracut-shutdown.service ├─graphical.target │ ├─systemd-readahead-done.service │ ├─systemd-readahead-done.timer │ └─systemd-update-utmp-runlevel.service └─shutdown.target ├─systemd-reboot.service └─final.target └─systemd-reboot.service 9.2.3. Starting a Service To start a service unit that corresponds to a system service type the following at a shell prompt as root: systemctl start name.service Replace name with the name of the service unit you want to start for example gdm. This command starts the selected service unit in the current session. For information on how to enable a service unit to be started at boot time see Section 9.2.6 “Enabling a Service”. For information on how to determine the status of a certain service unit see Section 9.2.2 “Displaying Service Status”. Example 9 .5. Starting a Service The service unit for the Apache HTTP Server is named httpd.service. To activate this service unit and start the httpd daemon in the current session run the following command as root: systemctl start httpd.service 9.2.4 . Stopping a Service To stop a service unit that corresponds to a system service type the following at a shell prompt as root: systemctl stop name.service Replace name with the name of the service unit you want to stop for example bluetooth. This command stops the selected service unit in the current session. For information on how to disable a Syst em Administ rat ors Guide 102

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service unit and prevent it from being started at boot time see Section 9.2.7 “Disabling a Service”. For information on how to determine the status of a certain service unit see Section 9.2.2 “Displaying Service Status”. Example 9 .6 . Stopping a Service The service unit for the bluetoothd daemon is named bluetooth.service. To deactivate this service unit and stop the bluetoothd daemon in the current session run the following command as root: systemctl stop bluetooth.service 9.2.5. Restarting a Service To restart a service unit that corresponds to a system service type the following at a shell prompt as root: systemctl restart name.service Replace name with the name of the service unit you want to restart for example httpd. This command stops the selected service unit in the current session and immediately starts it again. Importantly if the selected service unit is not running this command starts it too. To tell systemd to restart a service unit only if the corresponding service is already running run the following command as root: systemctl try-restart name.service Certain system services also allow you to reload their configuration without interrupting their execution. To do so type as root: systemctl reload name.service Note that system services that do not support this feature ignore this command altogether. For convenience the systemctl command also supports the reload-or-restart and reload-or- try-restart commands that restart such services instead. For information on how to determine the status of a certain service unit see Section 9.2.2 “Displaying Service Status”. Example 9 .7. Restarting a Service In order to prevent users from encountering unnecessary error messages or partially rendered web pages the Apache HTTP Server allows you to edit and reload its configuration without the need to restart it and interrupt actively processed requests. To do so type the following at a shell prompt as root: systemctl reload httpd.service 9.2.6. Enabling a Service ⁠Chapt er 9 . Managing Services wit h syst emd 103

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To configure a service unit that corresponds to a system service to be automatically started at boot time type the following at a shell prompt as root: systemctl enable name.service Replace name with the name of the service unit you want to enable for example httpd. This command reads the Install section of the selected service unit and creates appropriate symbolic links to the /usr/lib/systemd/system/name.service file in the /etc/systemd/system/ directory and its subdirectories. This command does not however rewrite links that already exist. If you want to ensure that the symbolic links are re-created use the following command as root: systemctl reenable name.service This command disables the selected service unit and immediately enables it again. For information on how to determine whether a certain service unit is enabled to start at boot time see Section 9.2.2 “Displaying Service Status”. For information on how to start a service in the current session see Section 9.2.3 “Starting a Service”. Example 9 .8. Enabling a Service To configure the Apache HTTP Server to start automatically at boot time run the following command as root: systemctl enable httpd.service Created symlink from /etc/systemd/system/multi- user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service. 9.2.7. Disabling a Service To prevent a service unit that corresponds to a system service from being automatically started at boot time type the following at a shell prompt as root: systemctl disable name.service Replace name with the name of the service unit you want to disable for example bluetooth. This command reads the Install section of the selected service unit and removes appropriate symbolic links to the /usr/lib/systemd/system/name.service file from the /etc/systemd/system/ directory and its subdirectories. In addition you can mask any service unit to prevent it from being started manually or by another service. To do so run the following command as root: systemctl mask name.service This command replaces the /etc/systemd/system/name.service file with a symbolic link to /dev/null rendering the actual unit file inaccessible to systemd. To revert this action and unmask a service unit type as root: systemctl unmask name.service Syst em Administ rat ors Guide 104

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For information on how to determine whether a certain service unit is enabled to start at boot time see Section 9.2.2 “Displaying Service Status”. For information on how to stop a service in the current session see Section 9.2.4 “Stopping a Service”. Example 9 .9 . Disabling a Service Example 9.6 “Stopping a Service” illustrates how to stop the bluetooth.service unit in the current session. To prevent this service unit from starting at boot time type the following at a shell prompt as root: systemctl disable bluetooth.service Removed symlink /etc/systemd/system/bluetooth.target.wants/bluetooth.service. Removed symlink /etc/systemd/system/dbus-org.bluez.service. 9.3. Working with systemd Targets Previous versions of Red Hat Enterprise Linux which were distributed with SysV init or Upstart implemented a predefined set of runlevels that represented specific modes of operation. These runlevels were numbered from 0 to 6 and were defined by a selection of system services to be run when a particular runlevel was enabled by the system administrator. In Red Hat Enterprise Linux 7 the concept of runlevels has been replaced with systemd targets. Systemd targets are represented by target units. Target units end with the .target file extension and their only purpose is to group together other systemd units through a chain of dependencies. For example the graphical.target unit which is used to start a graphical session starts system services such as the GNOME Display Manager gdm.service or Accounts Service accounts- daemon.service and also activates the multi-user.target unit. Similarly the multi- user.target unit starts other essential system services such as NetworkManager NetworkManager.service or D-Bus dbus.service and activates another target unit named basic.target. Red Hat Enterprise Linux 7 is distributed with a number of predefined targets that are more or less similar to the standard set of runlevels from the previous releases of this system. For compatibility reasons it also provides aliases for these targets that directly map them to SysV runlevels. Table 9.6 “Comparison of SysV Runlevels with systemd Targets” provides a complete list of SysV runlevels and their corresponding systemd targets. Table 9 .6 . Comparison of SysV Runlevels with systemd Targets Runlevel Target Units Description 0 runlevel0.target poweroff.target Shut down and power off the system. 1 runlevel1.target rescue.target Set up a rescue shell. 2 runlevel2.target multi- user.target Set up a non-graphical multi-user system. 3 runlevel3.target multi- user.target Set up a non-graphical multi-user system. 4 runlevel4.target multi- user.target Set up a non-graphical multi-user system. 5 runlevel5.target graphical.target Set up a graphical multi-user system. ⁠Chapt er 9 . Managing Services wit h syst emd 105

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6 runlevel6.target reboot.target Shut down and reboot the system. Runlevel Target Units Description To view change or configure systemd targets use the systemctl utility as described in Table 9.7 “Comparison of SysV init Commands with systemctl” and in the sections below. The runlevel and telinit commands are still available in the system and work as expected but are only included for compatibility reasons and should be avoided. Table 9 .7. Comparison of SysV init Commands with systemctl Old Command New Command Description runlevel systemctl list-units --type target Lists currently loaded target units. telinit runlevel systemctl isolate name.target Changes the current target. 9.3.1. Viewing the Default T arget To determine which target unit is used by default run the following command: systemctl get-default This command resolves the symbolic link located at /etc/systemd/system/default.target and displays the result. For information on how to change the default target see Section 9.3.3 “Changing the Default Target”. For information on how to list all currently loaded target units see Section 9.3.2 “Viewing the Current Target”. Example 9 .10. Viewing the Default Target To display the default target unit type: systemctl get-default graphical.target 9.3.2. Viewing the Current T arget To list all currently loaded target units type the following command at a shell prompt: systemctl list-units --type target For each target unit this commands displays its full name UNIT followed by a note whether the unit has been loaded LOAD its high-level ACTIVE and low-level SUB unit activation state and a short description DESCRIPTION. By default the systemctl list-units command displays only active units. If you want to list all loaded units regardless of their state run this command with the --all or -a command line option: systemctl list-units --type target --all See Section 9.3.1 “Viewing the Default Target” for information on how to display the default target. For information on how to change the current target see Section 9.3.4 “Changing the Current Target”. Syst em Administ rat ors Guide 106

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Example 9 .11. Viewing the Current Target To list all currently loaded target units run the following command: systemctl list-units --type target UNIT LOAD ACTIVE SUB DESCRIPTION basic.target loaded active active Basic System cryptsetup.target loaded active active Encrypted Volumes getty.target loaded active active Login Prompts graphical.target loaded active active Graphical Interface local-fs-pre.target loaded active active Local File Systems Pre local-fs.target loaded active active Local File Systems multi-user.target loaded active active Multi-User System network.target loaded active active Network paths.target loaded active active Paths remote-fs.target loaded active active Remote File Systems sockets.target loaded active active Sockets sound.target loaded active active Sound Card spice-vdagentd.target loaded active active Agent daemon for Spice guests swap.target loaded active active Swap sysinit.target loaded active active System Initialization time-sync.target loaded active active System Time Synchronized timers.target loaded active active Timers LOAD Reflects whether the unit definition was properly loaded. ACTIVE The high-level unit activation state i.e. generalization of SUB. SUB The low-level unit activation state values depend on unit type. 17 loaded units listed. Pass --all to see loaded but inactive units too. To show all installed unit files use systemctl list-unit-files. 9.3.3. Changing the Default T arget To configure the system to use a different target unit by default type the following at a shell prompt as root: systemctl set-default name.target Replace name with the name of the target unit you want to use by default for example multi-user. This command replaces the /etc/systemd/system/default.target file with a symbolic link to /usr/lib/systemd/system/name.target where name is the name of the target unit you want to use. For information on how to change the current target see Section 9.3.4 “Changing the Current Target”. For information on how to list all currently loaded target units see Section 9.3.2 “Viewing the Current Target”. Example 9 .12. Changing the Default Target ⁠Chapt er 9 . Managing Services wit h syst emd 107

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To configure the system to use the multi-user.target unit by default run the following command as root: systemctl set-default multi-user.target rm /etc/systemd/system/default.target ln -s /usr/lib/systemd/system/multi-user.target /etc/systemd/system/default.target 9.3.4 . Changing the Current T arget To change to a different target unit in the current session type the following at a shell prompt as root: systemctl isolate name.target Replace name with the name of the target unit you want to use for example multi-user. This command starts the target unit named name and all dependent units and immediately stops all others. For information on how to change the default target see Section 9.3.3 “Changing the Default Target”. For information on how to list all currently loaded target units see Section 9.3.2 “Viewing the Current Target”. Example 9 .13. Changing the Current Target To turn off the graphical user interface and change to the multi-user.target unit in the current session run the following command as root: systemctl isolate multi-user.target 9.3.5. Changing to Rescue Mode Rescue mode provides a convenient single-user environment and allows you to repair your system in situations when it is unable to complete a regular booting process. In rescue mode the system attempts to mount all local file systems and start some important system services but it does not activate network interfaces or allow more users to be logged into the system at the same time. In Red Hat Enterprise Linux 7 rescue mode is equivalent to single user mode and requires the root password. To change the current target and enter rescue mode in the current session type the following at a shell prompt as root: systemctl rescue This command is similar to systemctl isolate rescue.target but it also sends an informative message to all users that are currently logged into the system. To prevent systemd from sending this message run this command with the --no-wall command line option: systemctl --no-wall rescue For information on how to enter emergency mode see Section 9.3.6 “Changing to Emergency Mode”. Syst em Administ rat ors Guide 108

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Example 9 .14 . Changing to Rescue Mode To enter rescue mode in the current session run the following command as root: systemctl rescue Broadcast message from rootlocalhost on pts/0 Fri 2013-10-25 18:23:15 CEST: The system is going down to rescue mode NOW 9.3.6. Changing to Emergency Mode Emergency mode provides the most minimal environment possible and allows you to repair your system even in situations when the system is unable to enter rescue mode. In emergency mode the system mounts the root file system only for reading does not attempt to mount any other local file systems does not activate network interfaces and only starts a few essential services. In Red Hat Enterprise Linux 7 emergency mode requires the root password. To change the current target and enter emergency mode type the following at a shell prompt as root: systemctl emergency This command is similar to systemctl isolate emergency.target but it also sends an informative message to all users that are currently logged into the system. To prevent systemd from sending this message run this command with the --no-wall command line option: systemctl --no-wall emergency For information on how to enter rescue mode see Section 9.3.5 “Changing to Rescue Mode”. Example 9 .15. Changing to Emergency Mode To enter emergency mode without sending a message to all users that are currently logged into the system run the following command as root: systemctl --no-wall emergency 9.4. Shutting Down Suspending and Hibernating the System In Red Hat Enterprise Linux 7 the systemctl utility replaces a number of power management commands used in previous versions of the Red Hat Enterprise Linux system. The commands listed in Table 9.8 “Comparison of Power Management Commands with systemctl” are still available in the system for compatibility reasons but it is advised that you use systemctl when possible. Table 9 .8. Comparison of Power Management Commands with systemctl Old Command New Command Description halt systemctl halt Halts the system. ⁠Chapt er 9 . Managing Services wit h syst emd 109

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poweroff systemctl poweroff Powers off the system. reboot systemctl reboot Restarts the system. pm-suspend systemctl suspend Suspends the system. pm-hibernate systemctl hibernate Hibernates the system. pm-suspend-hybrid systemctl hybrid- sleep Hibernates and suspends the system. Old Command New Command Description 9.4 .1. Shutting Down the System The systemctl utility provides commands for shutting down the system however the traditional shutdown command is also supported. Although the shutdown command will call the systemctl utility to perform the shutdown it has an advantage in that it also supports a time argument. This is particularly useful for scheduled maintenance and to allow more time for users to react to the warning that a system shutdown has been scheduled. The option to cancel the shutdown can also be an advantage. Using syst emct l Co mmands To shut down the system and power off the machine type the following at a shell prompt as root: systemctl poweroff To shut down and halt the system without powering off the machine run the following command as root: systemctl halt By default running either of these commands causes systemd to send an informative message to all users that are currently logged into the system. To prevent systemd from sending this message run the selected command with the --no-wall command line option for example: systemctl --no-wall poweroff Using t he shut do wn Co mmand To shut down the system and power off the machine at a certain time use a command in the following format as root: shutdown --poweroff hh:mm Where hh:mm is the time in 24 hour clock format. The /run/nologin file is created 5 minutes before system shutdown to prevent new logins. When a time argument is used an optional message the wall message can be appended to the command. To shut down and halt the system after a delay without powering off the machine use a command in the following format as root: shutdown --halt +m Where +m is the delay time in minutes. The now keyword is an alias for +0. Syst em Administ rat ors Guide 110

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A pending shutdown can be canceled by the root user as follows: shutdown -c See the shutdown8 manual page for further command options. 9.4 .2. Restarting the System To restart the system run the following command as root: systemctl reboot By default this command causes systemd to send an informative message to all users that are currently logged into the system. To prevent systemd from sending this message run this command with the --no-wall command line option: systemctl --no-wall reboot 9.4 .3. Suspending the System To suspend the system type the following at a shell prompt as root: systemctl suspend This command saves the system state in RAM and with the exception of the RAM module powers off most of the devices in the machine. When you turn the machine back on the system then restores its state from RAM without having to boot again. Because the system state is saved in RAM and not on the hard disk restoring the system from suspend mode is significantly faster than restoring it from hibernation but as a consequence a suspended system state is also vulnerable to power outages. For information on how to hibernate the system see Section 9.4.4 “Hibernating the System”. 9.4 .4 . Hibernating the System To hibernate the system type the following at a shell prompt as root: systemctl hibernate This command saves the system state on the hard disk drive and powers off the machine. When you turn the machine back on the system then restores its state from the saved data without having to boot again. Because the system state is saved on the hard disk and not in RAM the machine does not have to maintain electrical power to the RAM module but as a consequence restoring the system from hibernation is significantly slower than restoring it from suspend mode. To hibernate and suspend the system run the following command as root: systemctl hybrid-sleep For information on how to suspend the system see Section 9.4.3 “Suspending the System”. 9.5. Controlling systemd on a Remote Machine ⁠Chapt er 9 . Managing Services wit h syst emd 111

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In addition to controlling the systemd system and service manager locally the systemctl utility also allows you to interact with systemd running on a remote machine over the SSH protocol. Provided that the sshd service on the remote machine is running you can connect to this machine by running the systemctl command with the --host or -H command line option: systemctl --host user_namehost_name command Replace user_name with the name of the remote user host_name with the machines host name and command with any of the systemctl commands described above. Note that the remote machine must be configured to allow the selected user remote access over the SSH protocol. For more information on how to configure an SSH server see Chapter 10 OpenSSH. Example 9 .16 . Remote Management To log in to a remote machine named server-01.example.com as the root user and determine the current status of the httpd.service unit type the following at a shell prompt: systemctl -H rootserver-01.example.com status httpd.service systemd unit files -- update rootserver-01.example.coms password: httpd.service - The Apache HTTP Server Loaded: loaded /usr/lib/systemd/system/httpd.service enabled Active: active running since Fri 2013-11-01 13:58:56 CET 2h 48min ago Main PID: 649 Status: "Total requests: 0 Current requests/sec: 0 Current traffic: 0 B/sec" CGroup: /system.slice/httpd.service 9.6. Creating and Modifying systemd Unit Files A unit file contains configuration directives that describe the unit and define its behavior. Several systemctl commands work with unit files in the background. To make finer adjustments system administrator must edit or create unit files manually. Table 9.2 “Systemd Unit Files Locations” lists three main directories where unit files are stored on the system the /etc/systemd/system/ directory is reserved for unit files created or customized by the system administrator. Unit file names take the following form: unit_name.type_extension Here unit_name stands for the name of the unit and type_extension identifies the unit type see Table 9.1 “Available systemd Unit Types” for a complete list of unit types. For example there usually is sshd.service as well as sshd.socket unit present on your system. Unit files can be supplemented with a directory for additional configuration files. For example to add custom configuration options to sshd.service create the sshd.service.d/custom.conf file and insert additional directives there. For more information on configuration directories see Section 9.6.4 “Modifying Existing Unit Files”. Also the sshd.service.wants/ and sshd.service.requires/ directories can be created. These directories contain symbolic links to unit files that are dependencies of the sshd service. The symbolic links are automatically created either during installation according to Install unit file Syst em Administ rat ors Guide 112

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options see Table 9.11 “Important Install Section Options” or at runtime based on Unit options see Table 9.9 “Important Unit Section Options”. It is also possible to create these directories and symbolic links manually. Many unit file options can be set using the so called unit specifiers – wildcard strings that are dynamically replaced with unit parameters when the unit file is loaded. This enables creation of generic unit files that serve as templates for generating instantiated units. See Section 9.6.5 “Working with Instantiated Units” for details. 9.6.1. Understanding the Unit File Structure Unit files typically consist of three sections: Unit — contains generic options that are not dependent on the type of the unit. These options provide unit description specify the units behavior and set dependencies to other units. For a list of most frequently used Unit options see Table 9.9 “Important Unit Section Options”. unit type — if a unit has type-specific directives these are grouped under a section named after the unit type. For example service unit files contain the Service section see Table 9.10 “Important Service Section Options” for most frequently used Service options. Install — contains information about unit installation used by systemctl enable and disable commands see Table 9.11 “Important Install Section Options” for a list of Install options. Table 9 .9 . Important Unit Section Options Option ⁠ Description Description A meaningful description of the unit. This text is displayed for example in the output of the systemctl status command. Documentation Provides a list of URIs referencing documentation for the unit. After ⁠ Defines the order in which units are started. The unit starts only after the units specified in After are active. Unlike Requires After does not explicitly activate the specified units. The Before option has the opposite functionality to After. Requires Configures dependencies on other units. The units listed in Requires are activated together with the unit. If any of the required units fail to start the unit is not activated. Wants Configures weaker dependencies than Requires. If any of the listed units does not start successfully it has no impact on the unit activation. This is the recommended way to establish custom unit dependencies. Conflicts Configures negative dependencies an opposite to Requires. Table 9 .10. Important Service Section Options Option ⁠ Description a b a Fo r a co mp lete list o f o p tio ns co nfig urab le in the Unit sectio n see the systemd.unit5 manual p ag e. b In mo st cases it is sufficient to set o nly the o rd ering d ep end encies with After and Before unit file o p tio ns. If yo u also set a req uirement d ep end ency with Wants reco mmend ed o r Requires the o rd ering d ep end ency still need s to b e sp ecified . That is b ecause o rd ering and req uirement d ep end encies wo rk ind ep end ently fro m each o ther. a ⁠Chapt er 9 . Managing Services wit h syst emd 113

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Type Configures the unit process startup type that affects the functionality of ExecStart and related options. One of: simple – The default value. The process started with ExecStart is the main process of the service. forking – The process started with ExecStart spawns a child process that becomes the main process of the service. The parent process exits when the startup is complete. oneshot – This type is similar to simple but the process exits before starting consequent units. dbus – This type is similar to simple but consequent units are started only after the main process gains a D-Bus name. notify – This type is similar to simple but consequent units are started only after a notification message is sent via the sd_notify function. idle – similar to simple the actual execution of the service binary is delayed until all jobs are finished which avoids mixing the status output with shell output of services. ExecStart Specifies commands or scripts to be executed when the unit is started. ExecStartPre and ExecStartPost specify custom commands to be executed before and after ExecStart. Typeoneshot enables specifying multiple custom commands that are then executed sequentially. ExecStop Specifies commands or scripts to be executed when the unit is stopped. ExecReload Specifies commands or scripts to be executed when the unit is reloaded. Restart With this option enabled the service is restarted after its process exits with the exception of a clean stop by the systemctl command. RemainAfterExit If set to True the service is considered active even when all its processes exited. Default value is False. This option is especially useful if Typeoneshot is configured. Option ⁠ Description Table 9 .11. Important Install Section Options Option ⁠ Description Alias Provides a space-separated list of additional names for the unit. Most systemctl commands excluding systemctl enable can use aliases instead of the actual unit name. RequiredBy A list of units that depend on the unit. When this unit is enabled the units listed in RequiredBy gain a Require dependency on the unit. WantedBy A list of units that weakly depend on the unit. When this unit is enabled the units listed in WantedBy gain a Want dependency on the unit. Also Specifies a list of units to be installed or uninstalled along with the unit. DefaultInstance Limited to instantiated units this option specifies the default instance for which the unit is enabled. See Section 9.6.5 “Working with Instantiated Units” a Fo r a co mp lete list o f o p tio ns co nfig urab le in the Service sectio n see the systemd.service5 manual p ag e. a a Fo r a co mp lete list o f o p tio ns co nfig urab le in the Install sectio n see the systemd.unit5 manual p ag e. Syst em Administ rat ors Guide 114

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A whole range of options that can be used to fine tune the unit configuration Example 9.17 “postfix.service Unit File” shows an example of a service unit installed on the system. Moreover unit file options can be defined in a way that enables dynamic creation of units as described in Section 9.6.5 “Working with Instantiated Units”. Example 9 .17. postfix.service Unit File What follows is the content of the /usr/lib/systemd/system/postifix.service unit file as currently provided by the postfix package: Unit DescriptionPostfix Mail Transport Agent Aftersyslog.target network.target Conflictssendmail.service exim.service Service Typeforking PIDFile/var/spool/postfix/pid/master.pid EnvironmentFile-/etc/sysconfig/network ExecStartPre-/usr/libexec/postfix/aliasesdb ExecStartPre-/usr/libexec/postfix/chroot-update ExecStart/usr/sbin/postfix start ExecReload/usr/sbin/postfix reload ExecStop/usr/sbin/postfix stop Install WantedBymulti-user.target The Unit section describes the service specifies the ordering dependencies as well as conflicting units. In Service a sequence of custom scripts is specified to be executed during unit activation on stop and on reload. EnvironmentFile points to the location where environment variables for the service are defined PIDFile specifies a stable PID for the main process of the service. Finally the Install section lists units that depend on the service. 9.6.2. Creating Custom Unit Files There are several use cases for creating unit files from scratch: you could run a custom daemon create a second instance of some existing service as in Example 9.19 “Creating a second instance of the sshd service” or import a SysV init script more in Section 9.6.3 “Converting SysV Init Scripts to Unit Files”. On the other hand if you intend just to modify or extend the behavior of an existing unit use the instructions from Section 9.6.4 “Modifying Existing Unit Files”. The following procedure describes the general process of creating a custom service: 1. Prepare the executable file with the custom service. This can be a custom-created script or an executable delivered by a software provider. If required prepare a PID file to hold a constant PID for the main process of the custom service. It is also possible to include environment files to store shell variables for the service. Make sure the source script is executable by executing the chmod a+x and is not interactive. 2. Create a unit file in the /etc/systemd/system/ directory and make sure it has correct file permissions. Execute as root: touch /etc/systemd/system/name.service chmod 664 /etc/systemd/system/name.service ⁠Chapt er 9 . Managing Services wit h syst emd 115

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Replace name with a name of the service to be created. Note that file does not need to be executable. 3. Open the name.service file created in the previous step and add the service configuration options. There is a variety of options that can be used depending on the type of service you wish to create see Section 9.6.1 “Understanding the Unit File Structure”. The following is an example unit configuration for a network-related service: Unit Descriptionservice_description Afternetwork.target Service ExecStartpath_to_executable Typeforking PIDFilepath_to_pidfile Install WantedBydefault.target Where: service_description is an informative description that is displayed in journal log files and in the output of the systemctl status command. the After setting ensures that the service is started only after the network is running. Add a space-separated list of other relevant services or targets. path_to_executable stands for the path to the actual service executable. Typeforking is used for daemons that make the fork system call. The main process of the service is created with the PID specified in path_to_pidfile. Find other startup types in Table 9.10 “Important Service Section Options”. WantedBy states the target or targets that the service should be started under. Think of these targets as of a replacement of the older concept of runlevels see Section 9.3 “Working with systemd Targets” for details. 4. Notify systemd that a new name.service file exists by executing the following command as root: systemctl daemon-reload systemctl start name.service Warning Always run the systemctl daemon-reload command after creating new unit files or modifying existing unit files. Otherwise the systemctl start or systemctl enable commands could fail due to a mismatch between states of systemd and actual service unit files on disk. The name.service unit can now be managed as any other system service with commands described in Section 9.2 “Managing System Services”. Syst em Administ rat ors Guide 116

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Example 9 .18. Creating the emacs.service File When using the Emacs text editor it is often faster and more convenient to have it running in the background instead of starting a new instance of the program whenever editing a file. The following steps show how to create a unit file for Emacs so that it can be handled like a service. 1. Create a unit file in the /etc/systemd/system/ directory and make sure it has the correct file permissions. Execute as root: touch /etc/systemd/system/emacs.service chmod 664 /etc/systemd/system/emacs.service 2. Add the following content to the file: Unit DescriptionEmacs: the extensible self-documenting text editor Service Typeforking ExecStart/usr/bin/emacs --daemon ExecStop/usr/bin/emacsclient --eval "kill-emacs" EnvironmentSSH_AUTH_SOCKt/keyring/ssh Restartalways Install WantedBydefault.target With the above configuration the /usr/bin/emacs executable is started in daemon mode on service start. The SSH_AUTH_SOCK environment variable is set using the "t" unit specifier that stands for the runtime directory. The service also restarts the emacs process if it exits unexpectedly. 3. Execute the following commands to reload the configuration and start the custom service: systemctl daemon-reload systemctl start emacs.service As the editor is now registered as a systemd service you can use all standard systemctl commands. For example run systemctl status emacs to display the editors status or systemctl enable emacs to make the editor start automatically on system boot. Example 9 .19 . Creating a second instance of the sshd service System Administrators often need to configure and run multiple instances of a service. This is done by creating copies of the original service configuration files and modifying certain parameters to avoid conflicts with the primary instance of the service. The following procedure shows how to create a second instance of the sshd service: 1. Create a copy of the sshd_config file that will be used by the second daemon: cp /etc/ssh/sshd-second_config 2. Edit the sshd-second_config file created in the previous step to assign a different port number and PID file to the second daemon: ⁠Chapt er 9 . Managing Services wit h syst emd 117

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Port 22220 PidFile /var/run/sshd-second.pid See the sshd_config5 manual page for more information on Port and PidFile options. Make sure the port you choose is not in use by any other service. The PID file does not have to exist before running the service it is generated automatically on service start. 3. Create a copy of the systemd unit file for the sshd service: cp /usr/lib/systemd/system/sshd.service /etc/systemd/system/sshd-second.service 4. Alter the sshd-second.service created in the previous step as follows: a. Modify the Description option: DescriptionOpenSSH server second instance daemon b. Add sshd.service to services specified in the After option so that the second instance starts only after the first one has already started: Aftersyslog.target network.target auditd.service sshd.service c. The first instance of sshd includes key generation therefore remove the ExecStartPre/usr/sbin/sshd-keygen line. d. Add the -f /etc/ssh/sshd-second_config parameter to the sshd command so that the alternative configuration file is used: ExecStart/usr/sbin/sshd -D -f /etc/ssh/sshd-second_config OPTIONS e. After the above modifications the sshd-second.service should look as follows: Unit DescriptionOpenSSH server second instance daemon Aftersyslog.target network.target auditd.service sshd.service Service EnvironmentFile/etc/sysconfig/sshd ExecStart/usr/sbin/sshd -D -f /etc/ssh/sshd-second_config OPTIONS ExecReload/bin/kill -HUP MAINPID KillModeprocess Restarton-failure RestartSec42s Install WantedBymulti-user.target Syst em Administ rat ors Guide 118

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5. If using SELinux add the port for the second instance of sshd to SSH ports otherwise the second instance of sshd will be rejected to bind to the port: semanage port -a -t ssh_port_t -p tcp 22220 6. Enable sshd-second.service so that it starts automatically upon boot: systemctl enable sshd-second.service Verify if the sshd-second.service is running by using the systemctl status command. Also verify if the port is enabled correctly by connecting to the service: ssh -p 22220 userserver If the firewall is in use please make sure that it is configured appropriately in order to allow connections to the second instance of sshd. 9.6.3. Converting SysV Init Scripts to Unit Files Before taking time to convert a SysV init script to a unit file make sure that the conversion was not already done elsewhere. All core services installed on Red Hat Enterprise Linux 7 come with default unit files and the same applies for many third-party software packages. Converting an init script to a unit file requires analyzing the script and extracting the necessary information from it. Based on this data you can create a unit file as described in Section 9.6.2 “Creating Custom Unit Files”. As init scripts can vary greatly depending on the type of the service you might need to employ more configuration options for translation than outlined in this chapter. Note that some levels of customization that were available with init scripts are no longer supported by systemd units see Section 9.1.2 “Compatibility Changes”. The majority of information needed for conversion is provided in the scripts header. The following example shows the opening section of the init script used to start the postfix service on Red Hat Enterprise Linux 6: /bin/bash postfix Postfix Mail Transfer Agent chkconfig: 2345 80 30 description: Postfix is a Mail Transport Agent which is the program \ that moves mail from one machine to another. processname: master pidfile: /var/spool/postfix/pid/master.pid config: /etc/postfix/main.cf config: /etc/postfix/master.cf BEGIN INIT INFO Provides: postfix MTA Required-Start: local_fs network remote_fs Required-Stop: local_fs network remote_fs Default-Start: 2 3 4 5 Default-Stop: 0 1 6 Short-Description: start and stop postfix ⁠Chapt er 9 . Managing Services wit h syst emd 119

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Description: Postfix is a Mail Transport Agent which is the program that moves mail from one machine to another. END INIT INFO In the above example only lines starting with chkconfig and description are mandatory so you might not find the rest in different init files. The text enclosed between the BEGIN INIT INFO and END INIT INFO lines is called Linux Standard Base LSB header. If specified LSB headers contain directives defining the service description dependencies and default runlevels. What follows is an overview of analytic tasks aiming to collect the data needed for a new unit file. The postfix init script is used as an example see the resulting postfix unit file in Example 9.17 “postfix.service Unit File”. Finding t he Service Descript io n Find descriptive information about the script on the line starting with description. Use this description together with the service name in the Description option in the Unit section of the unit file. The LSB header might contain similar data on the Short-Description and Description lines. Finding Service Dependencies The LSB header might contain several directives that form dependencies between services. Most of them are translatable to systemd unit options see Table 9.12 “Dependency Options from the LSB Header” Table 9 .12. Dependency Options from the LSB Header LSB Option Description Unit File Equivalent Provides Specifies the boot facility name of the service that can be referenced in other init scripts with the "" prefix. This is no longer needed as unit files refer to other units by their file names. – Required-Start Contains boot facility names of required services. This is translated as an ordering dependency boot facility names are replaced with unit file names of corresponding services or targets they belong to. For example in case of postfix the Required-Start dependency on network was translated to the After dependency on network.target. After Before Should-Start Constitutes weaker dependencies than Required-Start. Failed Should-Start dependencies do not affect the service startup. After Before Required-Stop Should-Stop Constitute negative dependencies. Conflicts Finding Default T arget s o f t he Service The line starting with chkconfig contains three numerical values. The most important is the first number that represents the default runlevels in which the service is started. Use Table 9.6 “Comparison of SysV Runlevels with systemd Targets” to map these runlevels to equivalent systemd targets. Then list these targets in the WantedBy option in the Install section of the unit file. For example postfix was previously started in runlevels 2 3 4 and 5 which translates to multi- Syst em Administ rat ors Guide 120

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user.target and graphical.target on Red Hat Enterprise Linux 7. Note that the graphical.target depends on multiuser.target therefore it is not necessary to specify both as in Example 9.17 “postfix.service Unit File”. You might find information on default and forbidden runlevels also at Default-Start and Default-Stop lines in the LSB header. The other two values specified on the chkconfig line represent startup and shutdown priorities of the init script. These values are interpreted by systemd if it loads the init script but there is no unit file equivalent. Finding Files Used by t he Service Init scripts require loading a function library from a dedicated directory and allow importing configuration environment and PID files. Environment variables are specified on the line starting with config in the init script header which translates to the EnvironmentFile unit file option. The PID file specified on the pidfile init script line is imported to the unit file with the PIDFile option. The key information that is not included in the init script header is the path to the service executable and potentially some other files required by the service. In previous versions of Red Hat Enterprise Linux init scripts used a Bash case statement to define the behavior of the service on default actions such as start stop or restart as well as custom-defined actions. The following excerpt from the postfix init script shows the block of code to be executed at service start. conf_check -x /usr/sbin/postfix || exit 5 -d /etc/postfix || exit 6 -d /var/spool/postfix || exit 5 make_aliasesdb if "/usr/sbin/postconf -h alias_database" "hash:/etc/aliases" then /etc/aliases.db might be used by other MTA make sure nothing has touched it since our last newaliases call /etc/aliases -nt /etc/aliases.db || "ALIASESDB_STAMP" -nt /etc/aliases.db || "ALIASESDB_STAMP" -ot /etc/aliases.db || return /usr/bin/newaliases touch -r /etc/aliases.db "ALIASESDB_STAMP" else /usr/bin/newaliases fi start "EUID" "0" exit 4 Check that networking is up. NETWORKING "no" exit 1 conf_check Start daemons. echo -n "Starting postfix: " make_aliasesdb /dev/null 21 -x CHROOT_UPDATE CHROOT_UPDATE /usr/sbin/postfix start 2/dev/null 12 success || failure "prog start" RETVAL ⁠Chapt er 9 . Managing Services wit h syst emd 121

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RETVAL -eq 0 touch lockfile echo return RETVAL The extensibility of the init script allowed specifying two custom functions conf_check and make_aliasesdb that are called from the start function block. On closer look several external files and directories are mentioned in the above code: the main service executable /usr/sbin/postfix the /etc/postfix/ and /var/spool/postfix/ configuration directories as well as the /usr/sbin/postconf/ directory. Systemd supports only the predefined actions but enables executing custom executables with ExecStart ExecStartPre ExecStartPost ExecStop and ExecReload options. In case of postfix on Red Hat Enterprise Linux 7 the /usr/sbin/postfix together with supporting scripts are executed on service start. Consult the postfix unit file at Example 9.17 “postfix.service Unit File”. Converting complex init scripts requires understanding the purpose of every statement in the script. Some of the statements are specific to the operating system version therefore you do not need to translate them. On the other hand some adjustments might be needed in the new environment both in unit file as well as in the service executable and supporting files. 9.6.4 . Modifying Existing Unit Files Services installed on the system come with default unit files that are stored in the /usr/lib/systemd/system/ directory. System Administrators should not modify these files directly therefore any customization must be confined to configuration files in the /etc/systemd/system/ directory. Depending on the extent of the required changes pick one of the following approaches: Create a directory for supplementary configuration files at /etc/systemd/system/unit.d/. This method is recommended for most use cases. It enables extending the default configuration with additional functionality while still referring to the original unit file. Changes to the default unit introduced with a package upgrade are therefore applied automatically. See Section 9.6.4 “Extending the Default Unit Configuration” for more information. Create a copy of the original unit file /usr/lib/systemd/system/ in /etc/systemd/system/ and make changes there. The copy overrides the original file therefore changes introduced with the package update are not applied. This method is useful for making significant unit changes that should persist regardless of package updates. See Section 9.6.4 “Overriding the Default Unit Configuration” for details. In order to return to the default configuration of the unit just delete custom-created configuration files in /etc/systemd/system/. To apply changes to unit files without rebooting the system execute: systemctl daemon-reload The daemon-reload option reloads all unit files and recreates the entire dependency tree which is needed to immediately apply any change to a unit file. As an alternative you can achieve the same result with the following command: init q Also if the modified unit file belongs to a running service this service must be restarted to accept new settings: Syst em Administ rat ors Guide 122

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systemctl restart name.service Important To modify properties such as dependencies or timeouts of a service that is handled by a SysV initscript do not modify the initscript itself. Instead create a systemd drop-in configuration file for the service as described in Section 9.6.4 “Extending the Default Unit Configuration” and Section 9.6.4 “Overriding the Default Unit Configuration”. Then manage this service in the same way as a normal systemd service. For example to extend the configuration of the network service do not modify the /etc/rc.d/init.d/network initscript file. Instead create new directory /etc/systemd/system/network.service.d/ and a systemd drop-in file /etc/systemd/system/network.service.d/my_config.conf. Then put the modified values into the drop-in file. Note: systemd knows the network service as network.service which is why the created directory must be called network.service.d Ext ending t he Default Unit Co nfigurat io n To extend the default unit file with additional configuration options first create a configuration directory in /etc/systemd/system/. If extending a service unit execute the following command as root: mkdir /etc/systemd/system/name.service.d/ Replace name with the name of the service you want to extend. The above syntax applies to all unit types. Create a configuration file in the directory made in the previous step. Note that the file name must end with the .conf suffix. Type: touch /etc/systemd/system/name.service.d/config_name.conf Replace config_name with the name of the configuration file. This file adheres to the normal unit file structure therefore all directives must be specified under appropriate sections see Section 9.6.1 “Understanding the Unit File Structure”. For example to add a custom dependency create a configuration file with the following content: Unit Requiresnew_dependency Afternew_dependency Where new_dependency stands for the unit to be marked as a dependency. Another example is a configuration file that restarts the service after its main process exited with a delay of 30 seconds: Service Restartalways RestartSec30 ⁠Chapt er 9 . Managing Services wit h syst emd 123

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It is recommended to create small configuration files focused only on one task. Such files can be easily moved or linked to configuration directories of other services. To apply changes made to the unit execute as root: systemctl daemon-reload systemctl restart name.service Example 9 .20. Extending the httpd.service Configuration To modify the httpd.service unit so that a custom shell script is automatically executed when starting the Apache service perform the following steps. First create a directory and a custom configuration file: mkdir /etc/systemd/system/httpd.service.d/ touch /etc/systemd/system/httpd.service.d/custom_script.conf Provided that the script you want to start automatically with Apache is located at /usr/local/bin/custom.sh insert the following text to the custom_script.conf file: Service ExecStartPost/usr/local/bin/custom.sh To apply the unit changes execute: systemctl daemon-reload systemctl restart httpd.service Note The configuration files from configuration directories in /etc/systemd/system/ take precedence over unit files in /usr/lib/systemd/system/. Therefore if the configuration files contain an option that can be specified only once such as Description or ExecStart the default value of this option is overridden. Note that in the output of the systemd-delta command described in Section 9.6.4 “Monitoring Overriden Units” such units are always marked as EXTENDED even though in sum certain options are actually overridden. Overriding t he Default Unit Co nfigurat io n To make changes that will persist after updating the package that provides the unit file first copy the file to the /etc/systemd/system/ directory. To do so execute the following command as root: cp /usr/lib/systemd/system/name.service /etc/systemd/system/name.service Where name stands for the name of the service unit you wish to modify. The above syntax applies to all unit types. Open the copied file with a text editor and make the desired changes. To apply the unit changes execute as root: Syst em Administ rat ors Guide 124

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systemctl daemon-reload systemctl restart name.service Example 9 .21. Changing the timeout limit You can specify a timeout value per service to prevent a malfunctioning service from freezing the system. Otherwise timeout is set by default to 90 seconds for normal services and to 300 seconds for SysV-compatible services. For example to extend timeout limit for the httpd service: 1. Copy the httpd unit file to the /etc/systemd/system/ directory: cp /usr/lib/systemd/system/httpd.service /etc/systemd/system/httpd.service 2. Open file /etc/systemd/system/httpd.service and specify the TimeoutStartUSec value in the Service section: ... Service ... PrivateTmptrue TimeoutStartSec10 Install WantedBymulti-user.target ... 3. Reload the systemd daemon: systemctl daemon-reload 4. Optional. Verify the new timeout value: systemctl show httpd -p TimeoutStartUSec Mo nit o ring Overriden Unit s To display an overview of overridden or modified unit files use the following command: systemd-delta For example the output of the above command can look as follows: EQUIVALENT /etc/systemd/system/default.target → /usr/lib/systemd/system/default.target OVERRIDDEN /etc/systemd/system/autofs.service → /usr/lib/systemd/system/autofs.service --- /usr/lib/systemd/system/autofs.service 2014-10-16 ⁠Chapt er 9 . Managing Services wit h syst emd 125

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21:30:39.000000000 -0400 +++ /etc/systemd/system/autofs.service 2014-11-21 10:00:58.513568275 - 0500 -87 +88 EnvironmentFile-/etc/sysconfig/autofs ExecStart/usr/sbin/automount OPTIONS --pid-file /run/autofs.pid ExecReload/usr/bin/kill -HUP MAINPID -TimeoutSec180 +TimeoutSec240 +RestartAlways Install WantedBymulti-user.target MASKED /etc/systemd/system/cups.service → /usr/lib/systemd/system/cups.service EXTENDED /usr/lib/systemd/system/sssd.service → /etc/systemd/system/sssd.service.d/journal.conf 4 overridden configuration files found. Table 9.13 “systemd-delta Difference Types” lists override types that can appear in the output of systemd-delta. Note that if a file is overridden systemd-delta by default displays a summary of changes similar to the output of the diff command. Table 9 .13. systemd-delta Difference Types Type Description MASKED Masked unit files see Section 9.2.7 “Disabling a Service” for description of unit masking. EQUIVALENT Unmodified copies that override the original files but do not differ in content typically symbolic links. REDIRECTED Files that are redirected to another file. OVERRIDEN Overridden and changed files. EXTENDED Files that are extended with .conf files in the /etc/systemd/system/unit.d/ directory. UNCHANGED Unmodified files are displayed only when the --typeunchanged option is used. It is good practice to run systemd-delta after system update to check if there are any updates to the default units that are currently overridden by custom configuration. It is also possible to limit the output only to a certain difference type. For example to view just the overridden units execute: systemd-delta --typeoverridden 9.6.5. Working with Instantiated Units It is possible to instantiate multiple units from a single template configuration file at runtime. The "" character is used to mark the template and to associate units with it. Instantiated units can be started from another unit file using Requires or Wants options or with the systemctl start command. Instantiated service units are named the following way: template_nameinstance_name.service Syst em Administ rat ors Guide 126

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Where template_name stands for the name of the template configuration file. Replace instance_name with the name for the unit instance. Several instances can point to the same template file with configuration options common for all instances of the unit. Template unit name has the form of: unit_name.service For example the following Wants setting in a unit file: WantsgettyttyA.servicegettyttyB.service first makes systemd search for given service units. If no such units are found the part between "" and the type suffix is ignored and systemd searches for the getty.service file reads the configuration from it and starts the services. Wildcard characters called unit specifiers can be used in any unit configuration file. Unit specifiers substitute certain unit parameters and are interpreted at runtime. Table 9.14 “Important Unit Specifiers” lists unit specifiers that are particularly useful for template units. Table 9 .14 . Important Unit Specifiers Unit Specifier Meaning Description n Full unit name Stands for the full unit name including the type suffix. N has the same meaning but also replaces the forbidden characters with ASCII codes. p Prefix name Stands for a unit name with type suffix removed. For instantiated units p stands for the part of the unit name before the "" character. i Instance name Is the part of the instantiated unit name between the "" character and the type suffix. I has the same meaning but also replaces the forbidden characters for ASCII codes. H Host name Stands for the hostname of the running system at the point in time the unit configuration is loaded. t Runtime directory Represents the runtime directory which is either /run for the root user or the value of the XDG_RUNTIME_DIR variable for unprivileged users. For a complete list of unit specifiers see the systemd.unit5 manual page. For example the getty.service template contains the following directives: Unit DescriptionGetty on I ... Service ExecStart-/sbin/agetty --noclear I TERM ... When the gettyttyA.service and gettyttyB.service are instantiated form the above template Description is resolved as Getty on ttyA and Getty on ttyB. 9.7. Additional Resources ⁠Chapt er 9 . Managing Services wit h syst emd 127

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For more information on systemd and its usage on Red Hat Enterprise Linux 7 see the resources listed below. Installed Documentation systemctl1 — The manual page for the systemctl command line utility provides a complete list of supported options and commands. systemd1 — The manual page for the systemd system and service manager provides more information about its concepts and documents available command line options and environment variables supported configuration files and directories recognized signals and available kernel options. systemd-delta1 — The manual page for the systemd-delta utility that allows to find extended and overridden configuration files. systemd.unit5 — The manual page named systemd.unit provides in-depth information about systemd unit files and documents all available configuration options. systemd.service5 — The manual page named systemd.service documents the format of service unit files. systemd.target5 — The manual page named systemd.target documents the format of target unit files. systemd.kill5 — The manual page named systemd.kill documents the configuration of the process killing procedure. Online Documentation Red Hat Enterprise Linux 7 Networking Guide — The Networking Guide for Red Hat Enterprise Linux 7 documents relevant information regarding the configuration and administration of network interfaces networks and network services in this system. It provides an introduction to the hostnamectl utility explains how to use it to view and set host names on the command line both locally and remotely and provides important information about the selection of host names and domain names. Red Hat Enterprise Linux 7 Desktop Migration and Administration Guide — The Desktop Migration and Administration Guide for Red Hat Enterprise Linux 7 documents the migration planning deployment configuration and administration of the GNOME 3 desktop on this system. It introduces the logind service enumerates its most significant features and explains how to use the loginctl utility to list active sessions and enable multi-seat support. Red Hat Enterprise Linux 7 SELinux Users and Administrators Guide — The SELinux Users and Administrators Guide for Red Hat Enterprise Linux 7 describes the basic principles of SELinux and documents in detail how to configure and use SELinux with various services such as the Apache HTTP Server Postfix PostgreSQL or OpenShift. It explains how to configure SELinux access permissions for system services managed by systemd. Red Hat Enterprise Linux 7 Installation Guide — The Installation Guide for Red Hat Enterprise Linux 7 documents how to install the system on AMD64 and Intel 64 systems 64-bit IBM Power Systems servers and IBM System z. It also covers advanced installation methods such as Kickstart installations PXE installations and installations over the VNC protocol. In addition it describes common post-installation tasks and explains how to troubleshoot installation problems including detailed instructions on how to boot into rescue mode or recover the root password. Red Hat Enterprise Linux 7 Security Guide — The Security Guide for Red Hat Enterprise Linux 7 Syst em Administ rat ors Guide 128

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assists users and administrators in learning the processes and practices of securing their workstations and servers against local and remote intrusion exploitation and malicious activity. It also explains how to secure critical system services. systemd Home Page — The project home page provides more information about systemd. See Also Chapter 1 System Locale and Keyboard Configuration documents how to manage the system locale and keyboard layouts. It explains how to use the localectl utility to view the current locale list available locales and set the system locale on the command line as well as to view the current keyboard layout list available keymaps and enable a particular keyboard layout on the command line. Chapter 2 Configuring the Date and Time documents how to manage the system date and time. It explains the difference between a real-time clock and system clock and describes how to use the timedatectl utility to display the current settings of the system clock configure the date and time change the time zone and synchronize the system clock with a remote server. Chapter 5 Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands. Chapter 10 OpenSSH describes how to configure an SSH server and how to use the ssh scp and sftp client utilities to access it. Chapter 20 Viewing and Managing Log Files provides an introduction to journald. It describes the journal introduces the journald service and documents how to use the journalctl utility to view log entries enter live view mode and filter log entries. In addition this chapter describes how to give non-root users access to system logs and enable persistent storage for log files. ⁠Chapt er 9 . Managing Services wit h syst emd 129

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Chapter 10. OpenSSH SSH Secure Shell is a protocol which facilitates secure communications between two systems using a client-server architecture and allows users to log in to server host systems remotely. Unlike other remote communication protocols such as FTP or Telnet SSH encrypts the login session rendering the connection difficult for intruders to collect unencrypted passwords. The ssh program is designed to replace older less secure terminal applications used to log in to remote hosts such as telnet or rsh. A related program called scp replaces older programs designed to copy files between hosts such as rcp. Because these older applications do not encrypt passwords transmitted between the client and the server avoid them whenever possible. Using secure methods to log in to remote systems decreases the risks for both the client system and the remote host. Red Hat Enterprise Linux includes the general OpenSSH package openssh as well as the OpenSSH server openssh-server and client openssh-clients packages. Note the OpenSSH packages require the OpenSSL package openssl-libs which installs several important cryptographic libraries enabling OpenSSH to provide encrypted communications. 10.1. The SSH Protocol 10.1.1. Why Use SSH Potential intruders have a variety of tools at their disposal enabling them to disrupt intercept and re- route network traffic in an effort to gain access to a system. In general terms these threats can be categorized as follows: Interception of communication between two systems The attacker can be somewhere on the network between the communicating parties copying any information passed between them. He may intercept and keep the information or alter the information and send it on to the intended recipient. This attack is usually performed using a packet sniffer a rather common network utility that captures each packet flowing through the network and analyzes its content. Impersonation of a particular host Attackers system is configured to pose as the intended recipient of a transmission. If this strategy works the users system remains unaware that it is communicating with the wrong host. This attack can be performed using a technique known as DNS poisoning or via so-called IP spoofing. In the first case the intruder uses a cracked DNS server to point client systems to a maliciously duplicated host. In the second case the intruder sends falsified network packets that appear to be from a trusted host. Both techniques intercept potentially sensitive information and if the interception is made for hostile reasons the results can be disastrous. If SSH is used for remote shell login and file copying these security threats can be greatly diminished. This is because the SSH client and server use digital signatures to verify their identity. Additionally all communication between the client and server systems is encrypted. Attempts to spoof the identity of either side of a communication does not work since each packet is encrypted using a key known only by the local and remote systems. 10.1.2. Main Features Syst em Administ rat ors Guide 130

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The SSH protocol provides the following safeguards: No one can pose as the intended server After an initial connection the client can verify that it is connecting to the same server it had connected to previously. No one can capture the authentication information The client transmits its authentication information to the server using strong 128-bit encryption. No one can intercept the communication All data sent and received during a session is transferred using 128-bit encryption making intercepted transmissions extremely difficult to decrypt and read. Additionally it also offers the following options: It provides secure means to use graphical applications over a network Using a technique called X11 forwarding the client can forward X11 X Window System applications from the server. It provides a way to secure otherwise insecure protocols The SSH protocol encrypts everything it sends and receives. Using a technique called port forwarding an SSH server can become a conduit to securing otherwise insecure protocols like POP and increasing overall system and data security. It can be used to create a secure channel The OpenSSH server and client can be configured to create a tunnel similar to a virtual private network for traffic between server and client machines. It supports the Kerberos authentication OpenSSH servers and clients can be configured to authenticate using the GSSAPI Generic Security Services Application Program Interface implementation of the Kerberos network authentication protocol. 10.1.3. Protocol Versions Two varieties of SSH currently exist: version 1 and newer version 2. The OpenSSH suite under Red Hat Enterprise Linux uses SSH version 2 which has an enhanced key exchange algorithm not vulnerable to the known exploit in version 1. However for compatibility reasons the OpenSSH suite does support version 1 connections as well. Important To ensure maximum security for your connection it is recommended that only SSH version 2- compatible servers and clients are used whenever possible. 10.1.4 . Event Sequence of an SSH Connection The following series of events help protect the integrity of SSH communication between two hosts. ⁠Chapt er 1 0 . OpenSSH 131

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1. A cryptographic handshake is made so that the client can verify that it is communicating with the correct server. 2. The transport layer of the connection between the client and remote host is encrypted using a symmetric cipher. 3. The client authenticates itself to the server. 4. The client interacts with the remote host over the encrypted connection. 10.1.4.1. T ranspo rt Layer The primary role of the transport layer is to facilitate safe and secure communication between the two hosts at the time of authentication and during subsequent communication. The transport layer accomplishes this by handling the encryption and decryption of data and by providing integrity protection of data packets as they are sent and received. The transport layer also provides compression speeding the transfer of information. Once an SSH client contacts a server key information is exchanged so that the two systems can correctly construct the transport layer. The following steps occur during this exchange: Keys are exchanged The public key encryption algorithm is determined The symmetric encryption algorithm is determined The message authentication algorithm is determined The hash algorithm is determined During the key exchange the server identifies itself to the client with a unique host key. If the client has never communicated with this particular server before the servers host key is unknown to the client and it does not connect. OpenSSH gets around this problem by accepting the servers host key. This is done after the user is notified and has both accepted and verified the new host key. In subsequent connections the servers host key is checked against the saved version on the client providing confidence that the client is indeed communicating with the intended server. If in the future the host key no longer matches the user must remove the clients saved version before a connection can occur. Warning It is possible for an attacker to masquerade as an SSH server during the initial contact since the local system does not know the difference between the intended server and a false one set up by an attacker. To help prevent this verify the integrity of a new SSH server by contacting the server administrator before connecting for the first time or in the event of a host key mismatch. SSH is designed to work with almost any kind of public key algorithm or encoding format. After an initial key exchange creates a hash value used for exchanges and a shared secret value the two systems immediately begin calculating new keys and algorithms to protect authentication and future data sent over the connection. Syst em Administ rat ors Guide 132

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After a certain amount of data has been transmitted using a given key and algorithm the exact amount depends on the SSH implementation another key exchange occurs generating another set of hash values and a new shared secret value. Even if an attacker is able to determine the hash and shared secret value this information is only useful for a limited period of time. 10.1.4.2. Aut hent icat io n Once the transport layer has constructed a secure tunnel to pass information between the two systems the server tells the client the different authentication methods supported such as using a private key-encoded signature or typing a password. The client then tries to authenticate itself to the server using one of these supported methods. SSH servers and clients can be configured to allow different types of authentication which gives each side the optimal amount of control. The server can decide which encryption methods it supports based on its security model and the client can choose the order of authentication methods to attempt from the available options. 10.1.4.3. Channels After a successful authentication over the SSH transport layer multiple channels are opened via a technique called multiplexing ⁠ . Each of these channels handles communication for different terminal sessions and for forwarded X11 sessions. Both clients and servers can create a new channel. Each channel is then assigned a different number on each end of the connection. When the client attempts to open a new channel the clients sends the channel number along with the request. This information is stored by the server and is used to direct communication to that channel. This is done so that different types of sessions do not affect one another and so that when a given session ends its channel can be closed without disrupting the primary SSH connection. Channels also support flow-control which allows them to send and receive data in an orderly fashion. In this way data is not sent over the channel until the client receives a message that the channel is open. The client and server negotiate the characteristics of each channel automatically depending on the type of service the client requests and the way the user is connected to the network. This allows great flexibility in handling different types of remote connections without having to change the basic infrastructure of the protocol. 10.2. Configuring OpenSSH 10.2.1. Configuration Files There are two different sets of configuration files: those for client programs that is ssh scp and sftp and those for the server the sshd daemon. System-wide SSH configuration information is stored in the /etc/ssh/ directory as described in Table 10.1 “System-wide configuration files”. User-specific SSH configuration information is stored in /.ssh/ within the users home directory as described in Table 10.2 “User-specific configuration files”. Table 10.1. System-wide configuration files File Description 1 ⁠Chapt er 1 0 . OpenSSH 133

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/etc/ssh/moduli Contains Diffie-Hellman groups used for the Diffie-Hellman key exchange which is critical for constructing a secure transport layer. When keys are exchanged at the beginning of an SSH session a shared secret value is created which cannot be determined by either party alone. This value is then used to provide host authentication. /etc/ssh/ssh_config The default SSH client configuration file. Note that it is overridden by /.ssh/config if it exists. /etc/ssh/sshd_config The configuration file for the sshd daemon. /etc/ssh/ssh_host_ecdsa_key The ECDSA private key used by the sshd daemon. /etc/ssh/ssh_host_ecdsa_key .pub The ECDSA public key used by the sshd daemon. /etc/ssh/ssh_host_key The RSA private key used by the sshd daemon for version 1 of the SSH protocol. /etc/ssh/ssh_host_key.pub The RSA public key used by the sshd daemon for version 1 of the SSH protocol. /etc/ssh/ssh_host_rsa_key The RSA private key used by the sshd daemon for version 2 of the SSH protocol. /etc/ssh/ssh_host_rsa_key.p ub The RSA public key used by the sshd daemon for version 2 of the SSH protocol. /etc/pam.d/sshd The PAM configuration file for the sshd daemon. /etc/sysconfig/sshd Configuration file for the sshd service. File Description Table 10.2. User-specific configuration files File Description /.ssh/authorized_keys Holds a list of authorized public keys for servers. When the client connects to a server the server authenticates the client by checking its signed public key stored within this file. /.ssh/id_ecdsa Contains the ECDSA private key of the user. /.ssh/id_ecdsa.pub The ECDSA public key of the user. /.ssh/id_rsa The RSA private key used by ssh for version 2 of the SSH protocol. /.ssh/id_rsa.pub The RSA public key used by ssh for version 2 of the SSH protocol. /.ssh/identity The RSA private key used by ssh for version 1 of the SSH protocol. /.ssh/identity.pub The RSA public key used by ssh for version 1 of the SSH protocol. /.ssh/known_hosts Contains host keys of SSH servers accessed by the user. This file is very important for ensuring that the SSH client is connecting to the correct SSH server. For information concerning various directives that can be used in the SSH configuration files see the ssh_config5 and sshd_config5 manual pages. 10.2.2. Starting an OpenSSH Server In order to run an OpenSSH server you must have the openssh-server package installed. For more information on how to install new packages see Section 8.2.4 “Installing Packages”. Syst em Administ rat ors Guide 134

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To start the sshd daemon in the current session type the following at a shell prompt as root: systemctl start sshd.service To stop the running sshd daemon in the current session use the following command as root: systemctl stop sshd.service If you want the daemon to start automatically at boot time type as root: systemctl enable sshd.service Created symlink from /etc/systemd/system/multi- user.target.wants/sshd.service to /usr/lib/systemd/system/sshd.service. The sshd daemon depends on the network.target target unit which is sufficient for static configured network interfaces and for default ListenAddress 0.0.0.0 options. To specify different addresses in the ListenAddress directive and to use a slower dynamic network configuration add dependency on the network-online.target target unit to the sshd.service unit file. To achieve this create the /etc/systemd/system/sshd.service.d/local.conf file with the following options: Unit Wantsnetwork-online.target Afternetwork-online.target After this reload the systemd manager configuration using the following command: systemctl daemon-reload For more information on how to manage system services in Red Hat Enterprise Linux see Chapter 9 Managing Services with systemd. Note that if you reinstall the system a new set of identification keys will be created. As a result clients who had connected to the system with any of the OpenSSH tools before the reinstall will see the following message: WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY Someone could be eavesdropping on you right now man-in-the-middle attack It is also possible that the RSA host key has just been changed. To prevent this you can backup the relevant files from the /etc/ssh/ directory. See Table 10.1 “System-wide configuration files” for a complete list and restore the files whenever you reinstall the system. 10.2.3. Requiring SSH for Remote Connections For SSH to be truly effective using insecure connection protocols should be prohibited. Otherwise a users password may be protected using SSH for one session only to be captured later while logging in using Telnet. Some services to disable include telnet rsh rlogin and vsftpd. ⁠Chapt er 1 0 . OpenSSH 135

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For information on how to configure the vsftpd service see Section 14.2 “FTP”. To learn how to manage system services in Red Hat Enterprise Linux 7 read Chapter 9 Managing Services with systemd. 10.2.4 . Using Key-based Authentication To improve the system security even further generate SSH key pairs and then enforce key-based authentication by disabling password authentication. To do so open the /etc/ssh/sshd_config configuration file in a text editor such as vi or nano and change the PasswordAuthentication option as follows: PasswordAuthentication no If you are working on a system other than a new default installation check that PubkeyAuthentication no has not been set. If connected remotely not using console or out-of- band access testing the key-based log in process before disabling password authentication is advised. To be able to use ssh scp or sftp to connect to the server from a client machine generate an authorization key pair by following the steps below. Note that keys must be generated for each user separately. Red Hat Enterprise Linux 7 uses SSH Protocol 2 and RSA keys by default see Section 10.1.3 “Protocol Versions” for more information. Important If you complete the steps as root only root will be able to use the keys. Note If you reinstall your system and want to keep previously generated key pairs backup the /.ssh/ directory. After reinstalling copy it back to your home directory. This process can be done for all users on your system including root. 10.2.4.1. Generat ing Key Pairs To generate an RSA key pair for version 2 of the SSH protocol follow these steps: 1. Generate an RSA key pair by typing the following at a shell prompt: ssh-keygen -t rsa Generating public/private rsa key pair. Enter file in which to save the key /home/USER/.ssh/id_rsa: 2. Press Enter to confirm the default location /.ssh/id_rsa for the newly created key. 3. Enter a passphrase and confirm it by entering it again when prompted to do so. For security reasons avoid using the same password as you use to log in to your account. After this you will be presented with a message similar to this: Syst em Administ rat ors Guide 136

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Your identification has been saved in /home/USER/.ssh/id_rsa. Your public key has been saved in /home/USER/.ssh/id_rsa.pub. The key fingerprint is: e7:97:c7:e2:0e:f9:0e:fc:c4:d7:cb:e5:31:11:92:14 USERpenguin.example.com The keys randomart image is: +-- RSA 2048----+ | E. | | . . | | o . | | . .| | S . . | | + o o ..| | +oo| | O +..| | o o.| +-----------------+ 4. By default the permissions of the /.ssh/ directory are set to rwx------ or 700 expressed in octal notation. This is to ensure that only the USER can view the contents. If required this can be confirmed with the following command: ls -ld /.ssh drwx------. 2 USER USER 54 Nov 25 16:56 /home/USER/.ssh/ 5. To copy the public key to a remote machine issue a command in the following format: ssh-copy-id userhostname This will copy the most recently modified /.ssh/id.pub public key if it is not yet installed. Alternatively specify the public keys file name as follows: ssh-copy-id -i /.ssh/id_rsa.pub userhostname This will copy the content of /.ssh/id_rsa.pub into the /.ssh/authorized_keys file on the machine to which you want to connect. If the file already exists the keys are appended to its end. To generate an ECDSA key pair for version 2 of the SSH protocol follow these steps: 1. Generate an ECDSA key pair by typing the following at a shell prompt: ssh-keygen -t ecdsa Generating public/private ecdsa key pair. Enter file in which to save the key /home/USER/.ssh/id_ecdsa: 2. Press Enter to confirm the default location /.ssh/id_ecdsa for the newly created key. 3. Enter a passphrase and confirm it by entering it again when prompted to do so. For security reasons avoid using the same password as you use to log in to your account. After this you will be presented with a message similar to this: Your identification has been saved in /home/USER/.ssh/id_ecdsa. Your public key has been saved in /home/USER/.ssh/id_ecdsa.pub. ⁠Chapt er 1 0 . OpenSSH 137

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The key fingerprint is: fd:1d:ca:10:52:96:21:43:7e:bd:4c:fc:5b:35:6b:63 USERpenguin.example.com The keys randomart image is: +--ECDSA 256---+ | .+ +o | | . .o | | o o + ..| | + + o +| | S o o oE.| | + oo+.| | + o | | | | | +-----------------+ 4. By default the permissions of the /.ssh/ directory are set to rwx------ or 700 expressed in octal notation. This is to ensure that only the USER can view the contents. If required this can be confirmed with the following command: ls -ld /.ssh ls -ld /.ssh/ drwx------. 2 USER USER 54 Nov 25 16:56 /home/USER/.ssh/ 5. To copy the public key to a remote machine issue a command in the following format: ssh-copy-id USERhostname This will copy the most recently modified /.ssh/id.pub public key if it is not yet installed. Alternatively specify the public keys file name as follows: ssh-copy-id -i /.ssh/id_ecdsa.pub USERhostname This will copy the content of /.ssh/id_ecdsa.pub into the /.ssh/authorized_keys on the machine to which you want to connect. If the file already exists the keys are appended to its end. See Section 10.2.4.2 “Configuring ssh-agent” for information on how to set up your system to remember the passphrase. Important The private key is for your personal use only and it is important that you never give it to anyone. 10.2.4.2. Co nfiguring ssh-agent To store your passphrase so that you do not have to enter it each time you initiate a connection with a remote machine you can use the ssh-agent authentication agent. If you are running GNOME you can configure it to prompt you for your passphrase whenever you log in and remember it during the whole session. Otherwise you can store the passphrase for a certain shell prompt. To save your passphrase during your GNOME session follow these steps: Syst em Administ rat ors Guide 138

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1. Make sure you have the openssh-askpass package installed. If not see Section 8.2.4 “Installing Packages” for more information on how to install new packages in Red Hat Enterprise Linux. 2. Press the Super key to enter the Activities Overview type Startup Applications and then press Enter. The Startup Applications Preferences tool appears. The tab containing a list of available startup programs will be shown by default. The Super key appears in a variety of guises depending on the keyboard and other hardware but often as either the Windows or Command key and typically to the left of the Spacebar. Figure 10.1. Startup Applications Preferences 3. Click the Add button on the right and enter /usr/bin/ssh-add in the Command field. Figure 10.2. Adding new application ⁠Chapt er 1 0 . OpenSSH 139

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4. Click Add and make sure the checkbox next to the newly added item is selected. Figure 10.3. Enabling the application 5. Log out and then log back in. A dialog box will appear prompting you for your passphrase. From this point on you should not be prompted for a password by ssh scp or sftp. Figure 10.4 . Entering a passphrase To save your passphrase for a certain shell prompt use the following command: ssh-add Enter passphrase for /home/USER/.ssh/id_rsa: Note that when you log out your passphrase will be forgotten. You must execute the command each Syst em Administ rat ors Guide 14 0

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time you log in to a virtual console or a terminal window. 10.3. OpenSSH Clients To connect to an OpenSSH server from a client machine you must have the openssh-clients package installed see Section 8.2.4 “Installing Packages” for more information on how to install new packages in Red Hat Enterprise Linux. 10.3.1. Using the ssh Utility The ssh utility allows you to log in to a remote machine and execute commands there. It is a secure replacement for the rlogin rsh and telnet programs. Similarly to the telnet command log in to a remote machine by using the following command: ssh hostname For example to log in to a remote machine named penguin.example.com type the following at a shell prompt: ssh penguin.example.com This will log you in with the same user name you are using on the local machine. If you want to specify a different user name use a command in the following form: ssh usernamehostname For example to log in to penguin.example.com as USER type: ssh USERpenguin.example.com The first time you initiate a connection you will be presented with a message similar to this: The authenticity of host penguin.example.com cant be established. ECDSA key fingerprint is 256 da:24:43:0b:2e:c1:3f:a1:84:13:92:01:52:b4:84:ff. Are you sure you want to continue connecting yes/no Users should always check if the fingerprint is correct before answering the question in this dialog. The user can ask the administrator of the server to confirm the key is correct. This should be done in a secure and previously agreed way. If the user has access to the servers host keys the fingerprint can be checked by using the ssh-keygen command as follows: ssh-keygen -l -f /etc/ssh/ssh_host_ecdsa_key.pub 256 da:24:43:0b:2e:c1:3f:a1:84:13:92:01:52:b4:84:ff ECDSA Type yes to accept the key and confirm the connection. You will see a notice that the server has been added to the list of known hosts and a prompt asking for your password: Warning: Permanently added penguin.example.com ECDSA to the list of known hosts. USERpenguin.example.coms password: ⁠Chapt er 1 0 . OpenSSH 14 1

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Important If the SSH servers host key changes the client notifies the user that the connection cannot proceed until the servers host key is deleted from the /.ssh/known_hosts file. Before doing this however contact the system administrator of the SSH server to verify the server is not compromised. To remove a key from the /.ssh/known_hosts file issue a command as follows: ssh-keygen -R penguin.example.com Host penguin.example.com found: line 15 type ECDSA /home/USER/.ssh/known_hosts updated. Original contents retained as /home/USER/.ssh/known_hosts.old After entering the password you will be provided with a shell prompt for the remote machine. Alternatively the ssh program can be used to execute a command on the remote machine without logging in to a shell prompt: ssh usernamehostname command For example the /etc/redhat-release file provides information about the Red Hat Enterprise Linux version. To view the contents of this file on penguin.example.com type: ssh USERpenguin.example.com cat /etc/redhat-release USERpenguin.example.coms password: Red Hat Enterprise Linux Server release 7.0 Maipo After you enter the correct password the user name will be displayed and you will return to your local shell prompt. 10.3.2. Using the scp Utility scp can be used to transfer files between machines over a secure encrypted connection. In its design it is very similar to rcp. To transfer a local file to a remote system use a command in the following form: scp localfile usernamehostname:remotefile For example if you want to transfer taglist.vim to a remote machine named penguin.example.com type the following at a shell prompt: scp taglist.vim USERpenguin.example.com:.vim/plugin/taglist.vim USERpenguin.example.coms password: taglist.vim 100 144KB 144.5KB/s 00:00 Multiple files can be specified at once. To transfer the contents of .vim/plugin/ to the same directory on the remote machine penguin.example.com type the following command: Syst em Administ rat ors Guide 14 2

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scp .vim/plugin/ USERpenguin.example.com:.vim/plugin/ USERpenguin.example.coms password: closetag.vim 100 13KB 12.6KB/s 00:00 snippetsEmu.vim 100 33KB 33.1KB/s 00:00 taglist.vim 100 144KB 144.5KB/s 00:00 To transfer a remote file to the local system use the following syntax: scp usernamehostname:remotefile localfile For instance to download the .vimrc configuration file from the remote machine type: scp USERpenguin.example.com:.vimrc .vimrc USERpenguin.example.coms password: .vimrc 100 2233 2.2KB/s 00:00 10.3.3. Using the sftp Utility The sftp utility can be used to open a secure interactive FTP session. In its design it is similar to ftp except that it uses a secure encrypted connection. To connect to a remote system use a command in the following form: sftp usernamehostname For example to log in to a remote machine named penguin.example.com with USER as a user name type: sftp USERpenguin.example.com USERpenguin.example.coms password: Connected to penguin.example.com. sftp After you enter the correct password you will be presented with a prompt. The sftp utility accepts a set of commands similar to those used by ftp see Table 10.3 “A selection of available sftp commands”. Table 10.3. A selection of available sftp commands Command Description ls directory List the content of a remote directory. If none is supplied a current working directory is used by default. cd directory Change the remote working directory to directory. mkdir directory Create a remote directory. rmdir path Remove a remote directory. put localfile remotefile Transfer localfile to a remote machine. get remotefile localfile Transfer remotefile from a remote machine. ⁠Chapt er 1 0 . OpenSSH 14 3

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For a complete list of available commands see the sftp1 manual page. 10.4. More Than a Secure Shell A secure command-line interface is just the beginning of the many ways SSH can be used. Given the proper amount of bandwidth X11 sessions can be directed over an SSH channel. Or by using TCP/IP forwarding previously insecure port connections between systems can be mapped to specific SSH channels. 10.4 .1. X11 Forwarding To open an X11 session over an SSH connection use a command in the following form: ssh -Y usernamehostname For example to log in to a remote machine named penguin.example.com with USER as a user name type: ssh -Y USERpenguin.example.com USERpenguin.example.coms password: When an X program is run from the secure shell prompt the SSH client and server create a new secure channel and the X program data is sent over that channel to the client machine transparently. Note that the X Window system must be installed on the remote system before X11 forwarding can take place. Enter the following command as root to install the X11 package group: yum group install "X Window System" For more information on package groups see Section 8.3 “Working with Package Groups”. X11 forwarding can be very useful. For example X11 forwarding can be used to create a secure interactive session of the Print Settings utility. To do this connect to the server using ssh and type: system-config-printer The Print Settings tool will appear allowing the remote user to safely configure printing on the remote system. 10.4 .2. Port Forwarding SSH can secure otherwise insecure TCP/IP protocols via port forwarding. When using this technique the SSH server becomes an encrypted conduit to the SSH client. Port forwarding works by mapping a local port on the client to a remote port on the server. SSH can map any port from the server to any port on the client. Port numbers do not need to match for this technique to work. Syst em Administ rat ors Guide 14 4

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Note Setting up port forwarding to listen on ports below 1024 requires root level access. To create a TCP/IP port forwarding channel which listens for connections on the localhost use a command in the following form: ssh -L local-port:remote-hostname:remote-port usernamehostname For example to check email on a server called mail.example.com using POP3 through an encrypted connection use the following command: ssh -L 1100:mail.example.com:110 mail.example.com Once the port forwarding channel is in place between the client machine and the mail server direct a POP3 mail client to use port 1100 on the localhost to check for new email. Any requests sent to port 1100 on the client system will be directed securely to the mail.example.com server. If mail.example.com is not running an SSH server but another machine on the same network is SSH can still be used to secure part of the connection. However a slightly different command is necessary: ssh -L 1100:mail.example.com:110 other.example.com In this example POP3 requests from port 1100 on the client machine are forwarded through the SSH connection on port 22 to the SSH server other.example.com. Then other.example.com connects to port 110 on mail.example.com to check for new email. Note that when using this technique only the connection between the client system and other.example.com SSH server is secure. Port forwarding can also be used to get information securely through network firewalls. If the firewall is configured to allow SSH traffic via its standard port that is port 22 but blocks access to other ports a connection between two hosts using the blocked ports is still possible by redirecting their communication over an established SSH connection. Important Using port forwarding to forward connections in this manner allows any user on the client system to connect to that service. If the client system becomes compromised the attacker also has access to forwarded services. System administrators concerned about port forwarding can disable this functionality on the server by specifying a No parameter for the AllowTcpForwarding line in /etc/ssh/sshd_config and restarting the sshd service. 10.5. Additional Resources For more information on how to configure or connect to an OpenSSH server on Red Hat Enterprise Linux see the resources listed below. ⁠Chapt er 1 0 . OpenSSH 14 5

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Installed Documentation sshd8 — The manual page for the sshd daemon documents available command line options and provides a complete list of supported configuration files and directories. ssh1 — The manual page for the ssh client application provides a complete list of available command line options and supported configuration files and directories. scp1 — The manual page for the scp utility provides a more detailed description of this utility and its usage. sftp1 — The manual page for the sftp utility. ssh-keygen1 — The manual page for the ssh-keygen utility documents in detail how to use it to generate manage and convert authentication keys used by ssh. ssh_config5 — The manual page named ssh_config documents available SSH client configuration options. sshd_config5 — The manual page named sshd_config provides a full description of available SSH daemon configuration options. Online Documentation OpenSSH Home Page — The OpenSSH home page containing further documentation frequently asked questions links to the mailing lists bug reports and other useful resources. OpenSSL Home Page — The OpenSSL home page containing further documentation frequently asked questions links to the mailing lists and other useful resources. See Also Chapter 5 Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands. Chapter 9 Managing Services with systemd provides more information on systemd and documents how to use the systemctl command to manage system services. 1 A multip lexed co nnectio n co nsists o f several sig nals b eing sent o ver a shared co mmo n med ium. With SSH d ifferent channels are sent o ver a co mmo n secure co nnectio n. Syst em Administ rat ors Guide 14 6

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Chapter 11. TigerVNC TigerVNC Tiger Virtual Network Computing is a system for graphical desktop sharing which allows you to remotely control other computers. TigerVNC works on the client-server principle: a server shares its output vncserver and a client vncviewer connects to the server. Note Unlike in previous Red Hat Enterprise Linux distributions TigerVNC in Red Hat Enterprise Linux 7 uses the systemd system management daemon for its configuration. The /etc/sysconfig/vncserver configuration file has been replaced by /etc/systemd/system/vncserver.service. 11.1. VNC Server vncserver is a utility which starts a VNC Virtual Network Computing desktop. It runs Xvnc with appropriate options and starts a window manager on the VNC desktop. vncserver allows users to run separate sessions in parallel on a machine which can then be accessed by any number of clients from anywhere. 11.1.1. Installing VNC Server To install the TigerVNC server issue the following command as root: yum install tigervnc-server 11.1.2. Configuring VNC Server The VNC server can be configured to start a display for one or more users provided that accounts for the users exist on the system with optional parameters such as for display settings network address and port and security settings. Procedure 11.1. Configuring a VNC Display for a Single User 1. A configuration file named /etc/systemd/system/vncserver.service is required. To create this file copy the /usr/lib/systemd/system/vncserver.service file as root: cp /usr/lib/systemd/system/vncserver.service /etc/systemd/system/vncserver.service There is no need to include the display number in the file name because systemd automatically creates the appropriately named instance in memory on demand replacing i in the service file by the display number. For a single user it is not necessary to rename the file. For multiple users a uniquely named service file for each user is required for example by adding the user name to the file name in some way. See Section 11.1.2.1 “Configuring VNC Server for Two Users” for details. ⁠Chapt er 1 1 . T igerVNC 14 7

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2. Edit /etc/systemd/system/vncserver.service replacing USER with the actual user name. Leave the remaining lines of the file unmodified. The -geometry argument specifies the size of the VNC desktop to be created by default it is set to 1024x768. ExecStart/usr/sbin/runuser -l USER -c "/usr/bin/vncserver i - geometry 1280x1024" PIDFile/home/USER/.vnc/Hi.pid 3. Save the changes. 4. To make the changes take effect immediately issue the following command: systemctl daemon-reload 5. Set the password for the user or users defined in the configuration file. Note that you need to switch from root to USER first. su - USER vncpasswd Password: Verify: Important The stored password is not encrypted anyone who has access to the password file can find the plain-text password. Proceed to Section 11.1.3 “Starting VNC Server”. 11.1.2.1. Co nfiguring VNC Server fo r T wo Users If you want to configure more than one user on the same machine create different template-type service files one for each user. 1. Create two service files for example vncserver-USER_1.service and vncserver-USER_2.service. In both these files substitute USER with the correct user name. 2. Set passwords for both users: su - USER_1 vncpasswd Password: Verify: su - USER_2 vncpasswd Password: Verify: 11.1.3. Starting VNC Server Syst em Administ rat ors Guide 14 8

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To start or enable the service specify the display number directly in the command. The file configured above in Procedure 11.1 “Configuring a VNC Display for a Single User” works as a template in which i is substituted with the display number by systemd. With a valid display number execute the following command: systemctl start vncserver:display_number.service You can also enable the service to start automatically at system start. Then when you log in vncserver is automatically started. As root issue a command as follows: systemctl enable vncserver:display_number.service At this point other users are able to use a VNC viewer program to connect to the VNC server using the display number and password defined. Provided a graphical desktop is installed an instance of that desktop will be displayed. It will not be the same instance as that currently displayed on the target machine. 11.1.3.1. Co nfiguring VNC Server fo r T wo Users and T wo Different Displays For the two configured VNC servers vncserver-USER_1.service and vncserver-USER_2.service you can enable different display numbers. For example the following commands will cause a VNC server for USER_1 to start on display 3 and a VNC server for USER_2 to start on display 5: systemctl start vncserver-USER_1:3.service systemctl start vncserver-USER_2:5.service 11.1.4 . VNC setup based on xinetd with XDMCP for GDM VNC setup based on xinetd with X Display Manager Control Protocol XDMCP for GDM is a useful setup for client systems that consist mainly of thin clients. After the setup clients are able to access the GDM login window and log in to any system account. The prerequisite for the setup is that the gdm vnc vnc-server and xinet packages are installed. yum install gdm tigervnc tigervnc-server xinet Service xinetd must be enabled. systemctl enable xinetd.service System default target unit should be graphical.target. To get the currently set default target unit use: systemctl get-default The default target unit can be changed by using: systemctl set-default target_name Procedure 11.2. Accessing the GDM login window and logging in 1. Set up GDM to enable XDMCP by editing the /etc/gdm/custom.conf configuration file: ⁠Chapt er 1 1 . T igerVNC 14 9

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xdmcp Enabletrue 2. Create a file called /etc/xinetd.d/xvncserver with the following content: service service_name disable no protocol tcp socket_type stream wait no user nobody server /usr/bin/Xvnc server_args -inetd -query localhost -once -geometry selected_geometry -depth selected_depth securitytypesnone In the server_args section the -query localhost option will make each Xvnc instance query localhost for an xdmcp session. The -depth option specifies the pixel depth in bits of the VNC desktop to be created. Acceptable values are 8 15 16 and 24 - any other values are likely to cause unpredictable behavior of applications. 3. Edit file /etc/services to have the service defined. To do this append the following snippet to the /etc/services file: VNC xinetd GDM base service_name 5950/tcp 4. To ensure that the configuration changes take effect reboot the machine. Alternatively you can run the following. Change init levels to 3 and back to 5 to force gdm to reload. init 3 init 5 Verify that gdm is listening on UDP port 177. netstat -anu|grep 177 udp 0 0 0.0.0.0:177 0.0.0.0: Restart the xinetd service. systemctl restart xinetd.service Verify that the xinetd service has loaded the new services. netstat -anpt|grep 595 tcp 0 0 :::5950 ::: LISTEN 3119/xinetd 5. Test the setup using a vncviewer command: Syst em Administ rat ors Guide 150

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vncviewer localhost:5950 The command will launch a VNC session to the localhost where no password is asked. You will see a GDM login screen and you will be able to log in to any user account on the system with a valid user name and password. Then you can run the same test on remote connections. Configure firewall for the setup. Run the firewall configuration tool and add TCP port 5950 to allow incoming connections to the system. firewall-cmd --permanent --zonepublic --add-port5950/tcp firewall-cmd --reload 11.1.5. T erminating a VNC Session Similarly to enabling the vncserver service you can disable the automatic start of the service at system start: systemctl disable vncserver:display_number.service Or when your system is running you can stop the service by issuing the following command as root: systemctl stop vncserver:display_number.service 11.2. Sharing an Existing Desktop By default a logged in user has a desktop provided by X Server on display 0. A user can share their desktop using the TigerVNC server x0vncserver. Procedure 11.3. Sharing an X Desktop To share the desktop of a logged in user using the x0vncserver proceed as follows: 1. Enter the following command as root yum install tigervnc-server 2. Set the VNC password for the user: vncpasswd Password: Verify: 3. Enter the following command as that user: x0vncserver -PasswordFile.vnc/passwd -AlwaysShared1 Provided the firewall is configured to allow connections to port 5900 the remote viewer can now connect to display 0 and view the logged in users desktop. See Section 11.3.2.1 “Configuring the Firewall for VNC” for information on how to configure the firewall. ⁠Chapt er 1 1 . T igerVNC 151

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11.3. VNC Viewer vncviewer is a program which shows the graphical user interfaces and controls the vncserver remotely. For operating the vncviewer there is a pop-up menu containing entries which perform various actions such as switching in and out of full-screen mode or quitting the viewer. Alternatively you can operate vncviewer through the terminal. Enter vncviewer -h on the command line to list vncviewers parameters. 11.3.1. Installing VNC Viewer To install the TigerVNC client vncviewer issue the following command as root: yum install tigervnc 11.3.2. Connecting to VNC Server Once the VNC server is configured you can connect to it from any VNC viewer. Procedure 11.4 . Connecting to a VNC Server Using a GUI 1. Enter the vncviewer command with no arguments the VNC Viewer: Connection Details utility appears. It prompts for a VNC server to connect to. 2. If required to prevent disconnecting any existing VNC connections to the same display select the option to allow sharing of the desktop as follows: a. Select the Options button. b. Select the Misc. tab. c. Select the Shared button. d. Press OK to return to the main menu. 3. Enter an address and display number to connect to: address:display_number 4. Press Connect to connect to the VNC server display. 5. You will be prompted to enter the VNC password. This will be the VNC password for the user corresponding to the display number unless a global default VNC password was set. A window appears showing the VNC server desktop. Note that this is not the desktop the normal user sees it is an Xvnc desktop. Procedure 11.5. Connecting to a VNC Server Using the CLI 1. Enter the viewer command with the address and display number as arguments: vncviewer address:display_number Where address is an IP address or host name. Syst em Administ rat ors Guide 152

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2. Authenticate yourself by entering the VNC password. This will be the VNC password for the user corresponding to the display number unless a global default VNC password was set. 3. A window appears showing the VNC server desktop. Note that this is not the desktop the normal user sees it is the Xvnc desktop. 11.3.2.1. Co nfiguring t he Firewall fo r VNC When using a non-encrypted connection firewalld might block the connection. To allow firewalld to pass the VNC packets you can open specific ports to TCP traffic. When using the - via option traffic is redirected over SSH which is enabled by default in firewalld. Note The default port of VNC server is 5900. To reach the port through which a remote desktop will be accessible sum the default port and the users assigned display number. For example for the second display: 2 + 5900 5902. For displays 0 to 3 make use of firewallds support for the VNC service by means of the service option as described below. Note that for display numbers greater than 3 the corresponding ports will have to be opened specifically as explained in Procedure 11.7 “Opening Ports in firewalld”. Procedure 11.6 . Enabling VNC Service in firewalld 1. Run the following command to see the information concerning firewalld settings: firewall-cmd --list-all 2. To allow all VNC connections from a specific address use a command as follows: firewall-cmd --add-rich-rulerule family"ipv4" source address"192.168.122.116" service namevnc-server accept success Note that these changes will not persist after the next system start. To make permanent changes to the firewall repeat the commands adding the --permanent option. See the Red Hat Enterprise Linux 7 Security Guide for more information on the use of firewall rich language commands. 3. To verify the above settings use a command as follows: firewall-cmd --list-all public default active interfaces: bond0 bond0.192 sources: services: dhcpv6-client ssh ports: masquerade: no forward-ports: icmp-blocks: rich rules: rule family"ipv4" source address"192.168.122.116" service name"vnc-server" accept ⁠Chapt er 1 1 . T igerVNC 153

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To open a specific port or range of ports make use of the --add-port option to the firewall-cmd command Line tool. For example VNC display 4 requires port 5904 to be opened for TCP traffic. Procedure 11.7. Opening Ports in firewalld 1. To open a port for TCP traffic in the public zone issue a command as root as follows: firewall-cmd --zonepublic --add-port5904/tcp success 2. To view the ports that are currently open for the public zone issue a command as follows: firewall-cmd --zonepublic --list-ports 5904/tcp A port can be removed using the firewall-cmd --zonezone --remove- portnumber/protocol command. Note that these changes will not persist after the next system start. To make permanent changes to the firewall repeat the commands adding the --permanent option. For more information on opening and closing ports in firewalld see the Red Hat Enterprise Linux 7 Security Guide. 11.3.3. Connecting to VNC Server Using SSH VNC is a clear text network protocol with no security against possible attacks on the communication. To make the communication secure you can encrypt your server-client connection by using the - via option. This will create an SSH tunnel between the VNC server and the client. The format of the command to encrypt a VNC server-client connection is as follows: vncviewer -via userhost:display_number Example 11.1. Using the -via Option 1. To connect to a VNC server using SSH enter a command as follows: vncviewer -via USER_2192.168.2.101:3 2. When you are prompted to type the password and confirm by pressing Enter. 3. A window with a remote desktop appears on your screen. Rest rict ing VNC Access If you prefer only encrypted connections you can prevent unencrypted connections altogether by using the -localhost option in the systemd.service file the ExecStart line: ExecStart/usr/sbin/runuser -l user -c "/usr/bin/vncserver -localhost i" This will stop vncserver from accepting connections from anything but the local host and port- forwarded connections sent using SSH as a result of the -via option. For more information on using SSH see Chapter 10 OpenSSH. Syst em Administ rat ors Guide 154

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11.4. Additional Resources For more information about TigerVNC see the resources listed below. Installed Documentation vncserver1 — The manual page for the VNC server utility. vncviewer1 — The manual page for the VNC viewer. vncpasswd1 — The manual page for the VNC password command. Xvnc1 — The manual page for the Xvnc server configuration options. x0vncserver1 — The manual page for the TigerVNC server for sharing existing X servers. ⁠Chapt er 1 1 . T igerVNC 155

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⁠Part V. Servers This part discusses various topics related to servers such as how to set up a web server or share files and directories over a network. Syst em Administ rat ors Guide 156

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Chapter 12. Web Servers A web server is a network service that serves content to a client over the web. This typically means web pages but any other documents can be served as well. Web servers are also known as HTTP servers as they use the hypertext transport protocol HTTP. 12.1. The Apache HTTP Server The web server available in Red Hat Enterprise Linux 7 is version 2.4 of the Apache HTTP Server httpd an open source web server developed by the Apache Software Foundation. If you are upgrading from a previous release of Red Hat Enterprise Linux you will need to update the httpd service configuration accordingly. This section reviews some of the newly added features outlines important changes between Apache HTTP Server 2.4 and version 2.2 and guides you through the update of older configuration files. 12.1.1. Notable Changes The Apache HTTP Server in Red Hat Enterprise Linux 7 has the following changes compared to Red Hat Enterprise Linux 6: httpd Service Control With the migration away from SysV init scripts server administrators should switch to using the apachectl and systemctl commands to control the service in place of the service command. The following examples are specific to the httpd service. The command: service httpd graceful is replaced by apachectl graceful The systemd unit file for httpd has different behavior from the init script as follows: A graceful restart is used by default when the service is reloaded. A graceful stop is used by default when the service is stopped. The command: service httpd configtest is replaced by apachectl configtest Private /tmp To enhance system security the systemd unit file runs the httpd daemon using a private /tmp directory separate to the system /tmp directory. ⁠Chapt er 1 2 . Web Servers 157

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Configuration Layout Configuration files which load modules are now placed in the /etc/httpd/conf.modules.d/ directory. Packages that provide additional loadable modules for httpd such as php will place a file in this directory. An Include directive before the main section of the /etc/httpd/conf/httpd.conf file is used to include files within the /etc/httpd/conf.modules.d/ directory. This means any configuration files within conf.modules.d/ are processed before the main body of httpd.conf. An IncludeOptional directive for files within the /etc/httpd/conf.d/ directory is placed at the end of the httpd.conf file. This means the files within /etc/httpd/conf.d/ are now processed after the main body of httpd.conf. Some additional configuration files are provided by the httpd package itself: /etc/httpd/conf.d/autoindex.conf — This configures mod_autoindex directory indexing. /etc/httpd/conf.d/userdir.conf — This configures access to user directories for example http://example.com/username/ such access is disabled by default for security reasons. /etc/httpd/conf.d/welcome.conf — As in previous releases this configures the welcome page displayed for http://localhost/ when no content is present. Default Configuration A minimal httpd.conf file is now provided by default. Many common configuration settings such as Timeout or KeepAlive are no longer explicitly configured in the default configuration hard-coded settings will be used instead by default. The hard-coded default settings for all configuration directives are specified in the manual. See Section 12.1.13 “Installable Documentation” for more information. Incompatible Syntax Changes If migrating an existing configuration from httpd 2.2 to httpd 2.4 a number of backwards-incompatible changes to the httpd configuration syntax were made which will require changes. See the following Apache document for more information on upgrading http://httpd.apache.org/docs/2.4/upgrading.html Processing Model In previous releases of Red Hat Enterprise Linux different multi-processing models MPM were made available as different httpd binaries: the forked model “prefork” as /usr/sbin/httpd and the thread-based model “worker” as /usr/sbin/httpd.worker. In Red Hat Enterprise Linux 7 only a single httpd binary is used and three MPMs are available as loadable modules: worker prefork default and event. Edit the configuration file /etc/httpd/conf.modules.d/00-mpm.conf as required by adding and removing the comment character so that only one of the three MPM modules is loaded. Packaging Changes The LDAP authentication and authorization modules are now provided in a separate sub- package mod_ldap. The new module mod_session and associated helper modules are provided in a new sub-package mod_session. The new modules mod_proxy_html and mod_xml2enc are provided in a new sub-package mod_proxy_html. These packages are all in the Optional channel. Syst em Administ rat ors Guide 158

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Note Before subscribing to the Optional and Supplementary channels see the Scope of Coverage Details. If you decide to install packages from these channels follow the steps documented in the article called How to access Optional and Supplementary channels and -devel packages using Red Hat Subscription Manager RHSM on the Red Hat Customer Portal. Packaging Filesystem Layout The /var/cache/mod_proxy/ directory is no longer provided instead the /var/cache/httpd/ directory is packaged with a proxy and ssl subdirectory. Packaged content provided with httpd has been moved from /var/www/ to /usr/share/httpd/: /usr/share/httpd/icons/ — The directory containing a set of icons used with directory indices previously contained in /var/www/icons/ has moved to /usr/share/httpd/icons/. Available at http://localhost/icons/ in the default configuration the location and the availability of the icons is configurable in the /etc/httpd/conf.d/autoindex.conf file. /usr/share/httpd/manual/ — The /var/www/manual/ has moved to /usr/share/httpd/manual/. This directory contained in the httpd-manual package contains the HTML version of the manual for httpd. Available at http://localhost/manual/ if the package is installed the location and the availability of the manual is configurable in the /etc/httpd/conf.d/manual.conf file. /usr/share/httpd/error/ — The /var/www/error/ has moved to /usr/share/httpd/error/. Custom multi-language HTTP error pages. Not configured by default the example configuration file is provided at /usr/share/doc/httpd-VERSION/httpd-multilang-errordoc.conf. Authentication Authoriz ation and Access Control The configuration directives used to control authentication authorization and access control have changed significantly. Existing configuration files using the Order Deny and Allow directives should be adapted to use the new Require syntax. See the following Apache document for more information http://httpd.apache.org/docs/2.4/howto/auth.html suexec To improve system security the suexec binary is no longer installed as if by the root user instead it has file system capability bits set which allow a more restrictive set of permissions. In conjunction with this change the suexec binary no longer uses the /var/log/httpd/suexec.log logfile. Instead log messages are sent to syslog by default these will appear in the /var/log/secure log file. Module Interface Third-party binary modules built against httpd 2.2 are not compatible with httpd 2.4 due to changes to the httpd module interface. Such modules will need to be adjusted as necessary for the httpd 2.4 module interface and then rebuilt. A detailed list of the API changes in version 2.4 is available here: http://httpd.apache.org/docs/2.4/developer/new_api_2_4.html. ⁠Chapt er 1 2 . Web Servers 159

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The apxs binary used to build modules from source has moved from /usr/sbin/apxs to /usr/bin/apxs. Removed modules List of httpd modules removed in Red Hat Enterprise Linux 7: mod_auth_mysql mod_auth_pgsql httpd 2.4 provides SQL database authentication support internally in the mod_authn_dbd module. mod_perl mod_perl is not officially supported with httpd 2.4 by upstream. mod_authz _ldap httpd 2.4 provides LDAP support in sub-package mod_ldap using mod_authnz _ldap. 12.1.2. Updating the Configuration To update the configuration files from the Apache HTTP Server version 2.2 take the following steps: 1. Make sure all module names are correct since they may have changed. Adjust the LoadModule directive for each module that has been renamed. 2. Recompile all third party modules before attempting to load them. This typically means authentication and authorization modules. 3. If you use the mod_userdir module make sure the UserDir directive indicating a directory name typically public_html is provided. 4. If you use the Apache HTTP Secure Server see Section 12.1.8 “Enabling the mod_ssl Module” for important information on enabling the Secure Sockets Layer SSL protocol. Note that you can check the configuration for possible errors by using the following command: apachectl configtest Syntax OK For more information on upgrading the Apache HTTP Server configuration from version 2.2 to 2.4 see http://httpd.apache.org/docs/2.4/upgrading.html. 12.1.3. Running the httpd Service This section describes how to start stop restart and check the current status of the Apache HTTP Server. To be able to use the httpd service make sure you have the httpd installed. You can do so by using the following command: yum install httpd For more information on the concept of targets and how to manage system services in Red Hat Enterprise Linux in general see Chapter 9 Managing Services with systemd. 12.1.3.1. St art ing t he Service Syst em Administ rat ors Guide 160

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To run the httpd service type the following at a shell prompt as root: systemctl start httpd.service If you want the service to start automatically at boot time use the following command: systemctl enable httpd.service Created symlink from /etc/systemd/system/multi- user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service. Note If running the Apache HTTP Server as a secure server a password may be required after the machine boots if using an encrypted private SSL key. 12.1.3.2. St o pping t he Service To stop the running httpd service type the following at a shell prompt as root: systemctl stop httpd.service To prevent the service from starting automatically at boot time type: systemctl disable httpd.service Removed symlink /etc/systemd/system/multi- user.target.wants/httpd.service. 12.1.3.3. Rest art ing t he Service There are three different ways to restart a running httpd service: 1. To restart the service completely enter the following command as root: systemctl restart httpd.service This stops the running httpd service and immediately starts it again. Use this command after installing or removing a dynamically loaded module such as PHP. 2. To only reload the configuration as root type: systemctl reload httpd.service This causes the running httpd service to reload its configuration file. Any requests currently being processed will be interrupted which may cause a client browser to display an error message or render a partial page. 3. To reload the configuration without affecting active requests enter the following command as root: apachectl graceful ⁠Chapt er 1 2 . Web Servers 161

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This causes the running httpd service to reload its configuration file. Any requests currently being processed will continue to use the old configuration. For more information on how to manage system services in Red Hat Enterprise Linux 7 see Chapter 9 Managing Services with systemd. 12.1.3.4. Verifying t he Service St at us To verify that the httpd service is running type the following at a shell prompt: systemctl is-active httpd.service active 12.1.4 . Editing the Configuration Files When the httpd service is started by default it reads the configuration from locations that are listed in Table 12.1 “The httpd service configuration files”. Table 12.1. The httpd service configuration files Path Description /etc/httpd/conf/httpd.c onf The main configuration file. /etc/httpd/conf.d/ An auxiliary directory for configuration files that are included in the main configuration file. Although the default configuration should be suitable for most situations it is a good idea to become at least familiar with some of the more important configuration options. Note that for any changes to take effect the web server has to be restarted first. See Section 12.1.3.3 “Restarting the Service” for more information on how to restart the httpd service. To check the configuration for possible errors type the following at a shell prompt: apachectl configtest Syntax OK To make the recovery from mistakes easier it is recommended that you make a copy of the original file before editing it. 12.1.5. Working with Modules Being a modular application the httpd service is distributed along with a number of Dynamic Shared Objects DSOs which can be dynamically loaded or unloaded at runtime as necessary. On Red Hat Enterprise Linux 7 these modules are located in /usr/lib64/httpd/modules/. 12.1.5.1. Lo ading a Mo dule To load a particular DSO module use the LoadModule directive. Note that modules provided by a separate package often have their own configuration file in the /etc/httpd/conf.d/ directory. Example 12.1. Loading the mod_ssl DSO LoadModule ssl_module modules/mod_ssl.so Syst em Administ rat ors Guide 162

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Once you are finished restart the web server to reload the configuration. See Section 12.1.3.3 “Restarting the Service” for more information on how to restart the httpd service. 12.1.5.2. Writ ing a Mo dule If you intend to create a new DSO module make sure you have the httpd-devel package installed. To do so enter the following command as root: yum install httpd-devel This package contains the include files the header files and the APache eXtenSion apxs utility required to compile a module. Once written you can build the module with the following command: apxs -i -a -c module_name.c If the build was successful you should be able to load the module the same way as any other module that is distributed with the Apache HTTP Server. 12.1.6. Setting Up Virtual Hosts The Apache HTTP Servers built in virtual hosting allows the server to provide different information based on which IP address host name or port is being requested. To create a name-based virtual host copy the example configuration file /usr/share/doc/httpd-VERSION/httpd-vhosts.conf into the /etc/httpd/conf.d/ directory and replace the Port and ServerRoot placeholder values. Customize the options according to your requirements as shown in Example 12.2 “Example virtual host configuration”. Example 12.2. Example virtual host configuration VirtualHost :80 ServerAdmin webmasterpenguin.example.com DocumentRoot "/www/docs/penguin.example.com" ServerName penguin.example.com ServerAlias www.penguin.example.com ErrorLog "/var/log/httpd/dummy-host.example.com-error_log" CustomLog "/var/log/httpd/dummy-host.example.com-access_log" common /VirtualHost Note that ServerName must be a valid DNS name assigned to the machine. The VirtualHost container is highly customizable and accepts most of the directives available within the main server configuration. Directives that are not supported within this container include User and Group which were replaced by SuexecUserGroup. ⁠Chapt er 1 2 . Web Servers 163

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Note If you configure a virtual host to listen on a non-default port make sure you update the Listen directive in the global settings section of the /etc/httpd/conf/httpd.conf file accordingly. To activate a newly created virtual host the web server has to be restarted first. See Section 12.1.3.3 “Restarting the Service” for more information on how to restart the httpd service. 12.1.7. Setting Up an SSL Server Secure Sockets Layer SSL is a cryptographic protocol that allows a server and a client to communicate securely. Along with its extended and improved version called Transport Layer Security TLS it ensures both privacy and data integrity. The Apache HTTP Server in combination with mod_ssl a module that uses the OpenSSL toolkit to provide the SSL/TLS support is commonly referred to as the SSL server. Red Hat Enterprise Linux also supports the use of Mozilla NSS as the TLS implementation. Support for Mozilla NSS is provided by the mod_nss module. Unlike an HTTP connection that can be read and possibly modified by anybody who is able to intercept it the use of SSL/TLS over HTTP referred to as HTTPS prevents any inspection or modification of the transmitted content. This section provides basic information on how to enable this module in the Apache HTTP Server configuration and guides you through the process of generating private keys and self-signed certificates. 12.1.7.1. An Overview o f Cert ificat es and Securit y Secure communication is based on the use of keys. In conventional or symmetric cryptography both ends of the transaction have the same key they can use to decode each others transmissions. On the other hand in public or asymmetric cryptography two keys co-exist: a private key that is kept a secret and a public key that is usually shared with the public. While the data encoded with the public key can only be decoded with the private key data encoded with the private key can in turn only be decoded with the public key. To provide secure communications using SSL an SSL server must use a digital certificate signed by a Certificate Authority CA. The certificate lists various attributes of the server that is the server host name the name of the company its location etc. and the signature produced using the CAs private key. This signature ensures that a particular certificate authority has signed the certificate and that the certificate has not been modified in any way. When a web browser establishes a new SSL connection it checks the certificate provided by the web server. If the certificate does not have a signature from a trusted CA or if the host name listed in the certificate does not match the host name used to establish the connection it refuses to communicate with the server and usually presents a user with an appropriate error message. By default most web browsers are configured to trust a set of widely used certificate authorities. Because of this an appropriate CA should be chosen when setting up a secure server so that target users can trust the connection otherwise they will be presented with an error message and will have to accept the certificate manually. Since encouraging users to override certificate errors can allow an attacker to intercept the connection you should use a trusted CA whenever possible. For more information on this see Table 12.2 “Information about CA lists used by common web browsers”. Table 12.2. Information about CA lists used by common web browsers Syst em Administ rat ors Guide 164

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Web Browser Link Moz illa Firefox Mozilla root CA list. Opera Information on root certificates used by Opera. Internet Explorer Information on root certificates used by Microsoft Windows. Chromium Information on root certificates used by the Chromium project. When setting up an SSL server you need to generate a certificate request and a private key and then send the certificate request proof of the companys identity and payment to a certificate authority. Once the CA verifies the certificate request and your identity it will send you a signed certificate you can use with your server. Alternatively you can create a self-signed certificate that does not contain a CA signature and thus should be used for testing purposes only. 12.1.8. Enabling the mod_ssl Module If you intend to set up an SSL or HTTPS server using mod_ssl you cannot have the another application or module such as mod_nss configured to use the same port. Port 443 is the default port for HTTPS. To set up an SSL server using the mod_ssl module and the OpenSSL toolkit install the mod_ssl and openssl packages. Enter the following command as root: yum install mod_ssl openssl This will create the mod_ssl configuration file at /etc/httpd/conf.d/ssl.conf which is included in the main Apache HTTP Server configuration file by default. For the module to be loaded restart the httpd service as described in Section 12.1.3.3 “Restarting the Service”. Important Due to the vulnerability described in POODLE: SSLv3 vulnerability CVE-2014-3566 Red Hat recommends disabling SSL and using only TLSv1.1 or TLSv1.2. Backwards compatibility can be achieved using TLSv1.0. Many products Red Hat supports have the ability to use SSLv2 or SSLv3 protocols or enable them by default. However the use of SSLv2 or SSLv3 is now strongly recommended against. 12.1.8.1. Enabling and Disabling SSL and T LS in mo d_ssl To disable and enable specific versions of the SSL and TLS protocol either do it globally by adding the SSLProtocol directive in the “ SSL Global Context” section of the configuration file and removing it everywhere else or edit the default entry under “ SSL Protocol support” in all “VirtualHost” sections. If you do not specify it in the per-domain VirtualHost section then it will inherit the settings from the global section. To make sure that a protocol version is being disabled the administrator should either only specify SSLProtocol in the “SSL Global Context” section or specify it in all per-domain VirtualHost sections. Procedure 12.1. Disable SSLv2 and SSLv3 To disable SSL version 2 and SSL version 3 which implies enabling everything except SSL version 2 and SSL version 3 in all VirtualHost sections proceed as follows: ⁠Chapt er 1 2 . Web Servers 165

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1. As root open the /etc/httpd/conf.d/ssl.conf file and search for all instances of the SSLProtocol directive. By default the configuration file contains one section that looks as follows: vi /etc/httpd/conf.d/ssl.conf SSL Protocol support: List the enable protocol levels with which clients will be able to connect. Disable SSLv2 access by default: SSLProtocol all -SSLv2 This section is within the VirtualHost section. 2. Edit the SSLProtocol line as follows: SSL Protocol support: List the enable protocol levels with which clients will be able to connect. Disable SSLv2 access by default: SSLProtocol all -SSLv2 -SSLv3 Repeat this action for all VirtualHost sections. Save and close the file. 3. Verify that all occurrences of the SSLProtocol directive have been changed as follows: grep SSLProtocol /etc/httpd/conf.d/ssl.conf SSLProtocol all -SSLv2 -SSLv3 This step is particularly important if you have more than the one default VirtualHost section. 4. Restart the Apache daemon as follows: systemctl restart httpd Note that any sessions will be interrupted. Procedure 12.2. Disable All SSL and TLS Protocols Except TLS 1 and Up To disable all SSL and TLS protocol versions except TLS version 1 and higher proceed as follows: 1. As root open the /etc/httpd/conf.d/ssl.conf file and search for all instances of SSLProtocol directive. By default the file contains one section that looks as follows: vi /etc/httpd/conf.d/ssl.conf SSL Protocol support: List the enable protocol levels with which clients will be able to connect. Disable SSLv2 access by default: SSLProtocol all -SSLv2 2. Edit the SSLProtocol line as follows: SSL Protocol support: List the enable protocol levels with which clients will be able to Syst em Administ rat ors Guide 166

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connect. Disable SSLv2 access by default: SSLProtocol -all +TLSv1 +TLSv1.1 +TLSv1.2 Save and close the file. 3. Verify the change as follows: grep SSLProtocol /etc/httpd/conf.d/ssl.conf SSLProtocol -all +TLSv1 +TLSv1.1 +TLSv1.2 4. Restart the Apache daemon as follows: systemctl restart httpd Note that any sessions will be interrupted. Procedure 12.3. Testing the Status of SSL and TLS Protocols To check which versions of SSL and TLS are enabled or disabled make use of the openssl s_client -connect command. The command has the following form: openssl s_client -connect hostname:port -protocol Where port is the port to test and protocol is the protocol version to test for. To test the SSL server running locally use localhost as the host name. For example to test the default port for secure HTTPS connections port 443 to see if SSLv3 is enabled issue a command as follows: 1. openssl s_client -connect localhost:443 -ssl3 CONNECTED00000003 139809943877536:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1257:SSL alert number 40 139809943877536:error:1409E0E5:SSL routines:SSL3_WRITE_BYTES:ssl handshake failure:s3_pkt.c:596: output omitted New NONE Cipher is NONE Secure Renegotiation IS NOT supported Compression: NONE Expansion: NONE SSL-Session: Protocol : SSLv3 output truncated The above output indicates that the handshake failed and therefore no cipher was negotiated. 2. openssl s_client -connect localhost:443 -tls1_2 CONNECTED00000003 depth0 C -- ST SomeState L SomeCity O SomeOrganization OU SomeOrganizationalUnit CN localhost.localdomain emailAddress rootlocalhost.localdomain output omitted New TLSv1/SSLv3 Cipher is ECDHE-RSA-AES256-GCM-SHA384 Server public key is 2048 bit Secure Renegotiation IS supported ⁠Chapt er 1 2 . Web Servers 167

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Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1.2 output truncated The above output indicates that no failure of the handshake occurred and a set of ciphers was negotiated. The openssl s_client command options are documented in the s_client1 manual page. For more information on the SSLv3 vulnerability and how to test for it see the Red Hat Knowledgebase article POODLE: SSLv3 vulnerability CVE-2014-3566. 12.1.9. Enabling the mod_nss Module If you intend to set up an HTTPS server using mod_nss you cannot have the mod_ssl package installed with its default settings as mod_ssl will use port 443 by default however this is the default HTTPS port. If at all possible remove the package. To remove mod_ssl enter the following command as root: yum remove mod_ssl Note If mod_ssl is required for other purposes modify the /etc/httpd/conf.d/ssl.conf file to use a port other than 443 to prevent mod_ssl conflicting with mod_nss when its port to listen on is changed to 443. Only one module can own a port therefore mod_nss and mod_ssl can only co-exist at the same time if they use unique ports. For this reason mod_nss by default uses 8443 but the default port for HTTPS is port 443. The port is specified by the Listen directive as well as in the VirtualHost name or address. Everything in NSS is associated with a “token”. The software token exists in the NSS database but you can also have a physical token containing certificates. With OpenSSL discrete certificates and private keys are held in PEM files. With NSS these are stored in a database. Each certificate and key is associated with a token and each token can have a password protecting it. This password is optional but if a password is used then the Apache HTTP server needs a copy of it in order to open the database without user intervention at system start. Procedure 12.4 . Configuring mod_nss 1. Install mod_nss as root: yum install mod_nss This will create the mod_nss configuration file at /etc/httpd/conf.d/nss.conf. The /etc/httpd/conf.d/ directory is included in the main Apache HTTP Server configuration file by default. For the module to be loaded restart the httpd service as described in Section 12.1.3.3 “Restarting the Service”. Syst em Administ rat ors Guide 168

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2. As root open the /etc/httpd/conf.d/nss.conf file and search for all instances of the Listen directive. Edit the Listen 8443 line as follows: Listen 443 Port 443 is the default port for HTTPS. 3. Edit the default VirtualHost _default_:8443 line as follows: VirtualHost _default_:443 Edit any other non-default virtual host sections if they exist. Save and close the file. 4. Mozilla NSS stores certificates in a server certificate database indicated by the NSSCertificateDatabase directive in the /etc/httpd/conf.d/nss.conf file. By default the path is set to /etc/httpd/alias the NSS database created during installation. To view the default NSS database issue a command as follows: certutil -L -d /etc/httpd/alias Certificate Nickname Trust Attributes SSLS/MIMEJAR/XPI cacert CTuCuCu Server-Cert uuu alpha upuu In the above command output Server-Cert is the default NSSNickname. The -L option lists all the certificates or displays information about a named certificate in a certificate database. The -d option specifies the database directory containing the certificate and key database files. See the certutil1 man page for more command line options. 5. To configure mod_nss to use another database edit the NSSCertificateDatabase line in the /etc/httpd/conf.d/nss.conf file. The default file has the following lines within the VirtualHost section. Server Certificate Database: The NSS security database directory that holds the certificates and keys. The database consists of 3 files: cert8.db key3.db and secmod.db. Provide the directory that these files exist. NSSCertificateDatabase /etc/httpd/alias In the above command output alias is the default NSS database directory /etc/httpd/alias/. 6. To apply a password to the default NSS certificate database use the following command as root: ⁠Chapt er 1 2 . Web Servers 169

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certutil -W -d /etc/httpd/alias Enter Password or Pin for "NSS Certificate DB": Enter a password which will be used to encrypt your keys. The password should be at least 8 characters long and should contain at least one non-alphabetic character. Enter new password: Re-enter password: Password changed successfully. 7. Before deploying the HTTPS server create a new certificate database using a certificate signed by a certificate authority CA. Example 12.3. Adding a Certificate to the Moz illa NSS database The certutil command is used to add a CA certificate to the NSS database files: certutil -d /etc/httpd/nss-db-directory/ -A -n "CA_certificate" - t CT -a -i certificate.pem The above command adds a CA certificate stored in a PEM-formatted file named certificate.pem. The -d option specifies the NSS database directory containing the certificate and key database files the -n option sets a name for the certificate -t CT means that the certificate is trusted to be used in TLS clients and servers. The -A option adds an existing certificate to a certificate database. If the database does not exist it will be created. The -a option allows the use of ASCII format for input or output and the -i option passes the certificate.pem input file to the command. See the certutil1 man page for more command line options. 8. The NSS database should be password protected to safeguard the private key. Example 12.4 . Setting a Password for a Moz illa NSS database The certutil tool can be used set a password for an NSS database as follows: certutil -W -d /etc/httpd/nss-db-directory/ For example for the default database issue a command as root as follows: certutil -W -d /etc/httpd/alias Enter Password or Pin for "NSS Certificate DB": Enter a password which will be used to encrypt your keys. The password should be at least 8 characters long and should contain at least one non-alphabetic character. Enter new password: Re-enter password: Password changed successfully. 9. Configure mod_nss to use the NSS internal software token by changing the line with the NSSPassPhraseDialog directive as follows: Syst em Administ rat ors Guide 170

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NSSPassPhraseDialog directive as follows: vi /etc/httpd/conf.d/nss.conf NSSPassPhraseDialog file:/etc/httpd/password.conf This is to avoid manual password entry on system start. The software token exists in the NSS database but you can also have a physical token containing your certificates. 10. If the SSL Server Certificate contained in the NSS database is an RSA certificate make certain that the NSSNickname parameter is uncommented and matches the nickname displayed in step 4 above: vi /etc/httpd/conf.d/nss.conf NSSNickname Server-Cert If the SSL Server Certificate contained in the NSS database is an ECC certificate make certain that the NSSECCNickname parameter is uncommented and matches the nickname displayed in step 4 above: vi /etc/httpd/conf.d/nss.conf NSSECCNickname Server-Cert Make certain that the NSSCertificateDatabase parameter is uncommented and points to the NSS database directory displayed in step 4 or configured in step 5 above: vi /etc/httpd/conf.d/nss.conf NSSCertificateDatabase /etc/httpd/alias Replace /etc/httpd/alias with the path to the certificate database to be used. 11. Create the /etc/httpd/password.conf file as root: vi /etc/httpd/password.conf Add a line with the following form: internal:password Replacing password with the password that was applied to the NSS security databases in step 6 above. 12. Apply the appropriate ownership and permissions to the /etc/httpd/password.conf file: chgrp apache /etc/httpd/password.conf chmod 640 /etc/httpd/password.conf ls -l /etc/httpd/password.conf -rw-r-----. 1 root apache 10 Dec 4 17:13 /etc/httpd/password.conf 13. To configure mod_nss to use the NSS the software token in /etc/httpd/password.conf edit /etc/httpd/conf.d/nss.conf as follows: vi /etc/httpd/conf.d/nss.conf ⁠Chapt er 1 2 . Web Servers 171

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14. Restart the Apache server for the changes to take effect as described in Section 12.1.3.3 “Restarting the Service” Important Due to the vulnerability described in POODLE: SSLv3 vulnerability CVE-2014-3566 Red Hat recommends disabling SSL and using only TLSv1.1 or TLSv1.2. Backwards compatibility can be achieved using TLSv1.0. Many products Red Hat supports have the ability to use SSLv2 or SSLv3 protocols or enable them by default. However the use of SSLv2 or SSLv3 is now strongly recommended against. 12.1.9.1. Enabling and Disabling SSL and T LS in mo d_nss To disable and enable specific versions of the SSL and TLS protocol either do it globally by adding the NSSProtocol directive in the “ SSL Global Context” section of the configuration file and removing it everywhere else or edit the default entry under “ SSL Protocol” in all “VirtualHost” sections. If you do not specify it in the per-domain VirtualHost section then it will inherit the settings from the global section. To make sure that a protocol version is being disabled the administrator should either only specify NSSProtocol in the “SSL Global Context” section or specify it in all per-domain VirtualHost sections. Procedure 12.5. Disable All SSL and TLS Protocols Except TLS 1 and Up in mod_nss To disable all SSL and TLS protocol versions except TLS version 1 and higher proceed as follows: 1. As root open the /etc/httpd/conf.d/nss.conf file and search for all instances of the NSSProtocol directive. By default the configuration file contains one section that looks as follows: vi /etc/httpd/conf.d/nss.conf SSL Protocol: output omitted Since all protocol ranges are completely inclusive and no protocol in the middle of a range may be excluded the entry "NSSProtocol SSLv3TLSv1.1" is identical to the entry "NSSProtocol SSLv3TLSv1.0TLSv1.1". NSSProtocol SSLv3TLSv1.0TLSv1.1 This section is within the VirtualHost section. 2. Edit the NSSProtocol line as follows: SSL Protocol: NSSProtocol TLSv1.0TLSv1.1 Repeat this action for all VirtualHost sections. 3. Edit the Listen 8443 line as follows: Listen 443 4. Edit the default VirtualHost _default_:8443 line as follows: Syst em Administ rat ors Guide 172

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VirtualHost _default_:443 Edit any other non-default virtual host sections if they exist. Save and close the file. 5. Verify that all occurrences of the NSSProtocol directive have been changed as follows: grep NSSProtocol /etc/httpd/conf.d/nss.conf middle of a range may be excluded the entry "NSSProtocol SSLv3TLSv1.1" is identical to the entry "NSSProtocol SSLv3TLSv1.0TLSv1.1". NSSProtocol TLSv1.0TLSv1.1 This step is particularly important if you have more than one VirtualHost section. 6. Restart the Apache daemon as follows: service httpd restart Note that any sessions will be interrupted. Procedure 12.6 . Testing the Status of SSL and TLS Protocols in mod_nss To check which versions of SSL and TLS are enabled or disabled in mod_nss make use of the openssl s_client -connect command. Install the openssl package as root: yum install openssl The openssl s_client -connect command has the following form: openssl s_client -connect hostname:port -protocol Where port is the port to test and protocol is the protocol version to test for. To test the SSL server running locally use localhost as the host name. For example to test the default port for secure HTTPS connections port 443 to see if SSLv3 is enabled issue a command as follows: 1. openssl s_client -connect localhost:443 -ssl3 CONNECTED00000003 3077773036:error:1408F10B:SSL routines:SSL3_GET_RECORD:wrong version number:s3_pkt.c:337: output omitted New NONE Cipher is NONE Secure Renegotiation IS NOT supported Compression: NONE Expansion: NONE SSL-Session: Protocol : SSLv3 output truncated The above output indicates that the handshake failed and therefore no cipher was negotiated. 2. openssl s_client -connect localhost:443 -tls1 CONNECTED00000003 depth1 C US O example.com CN Certificate Shack ⁠Chapt er 1 2 . Web Servers 173

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output omitted New TLSv1/SSLv3 Cipher is AES128-SHA Server public key is 1024 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1 output truncated The above output indicates that no failure of the handshake occurred and a set of ciphers was negotiated. The openssl s_client command options are documented in the s_client1 manual page. For more information on the SSLv3 vulnerability and how to test for it see the Red Hat Knowledgebase article POODLE: SSLv3 vulnerability CVE-2014-3566. 12.1.10. Using an Existing Key and Certificate If you have a previously created key and certificate you can configure the SSL server to use these files instead of generating new ones. There are only two situations where this is not possible: 1. You are changing the IP address or domain name. Certificates are issued for a particular IP address and domain name pair. If one of these values changes the certificate becomes invalid. 2. You have a certificate from VeriSign and you are changing the server software. VeriSign a widely used certificate authority issues certificates for a particular software product IP address and domain name. Changing the software product renders the certificate invalid. In either of the above cases you will need to obtain a new certificate. For more information on this topic see Section 12.1.11 “Generating a New Key and Certificate”. If you want to use an existing key and certificate move the relevant files to the /etc/pki/tls/private/ and /etc/pki/tls/certs/ directories respectively. You can do so by issuing the following commands as root: mv key_file.key /etc/pki/tls/private/hostname.key mv certificate.crt /etc/pki/tls/certs/hostname.crt Then add the following lines to the /etc/httpd/conf.d/ssl.conf configuration file: SSLCertificateFile /etc/pki/tls/certs/hostname.crt SSLCertificateKeyFile /etc/pki/tls/private/hostname.key To load the updated configuration restart the httpd service as described in Section 12.1.3.3 “Restarting the Service”. Example 12.5. Using a key and certificate from the Red Hat Secure Web Server Syst em Administ rat ors Guide 174

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mv /etc/httpd/conf/httpsd.key /etc/pki/tls/private/penguin.example.com.key mv /etc/httpd/conf/httpsd.crt /etc/pki/tls/certs/penguin.example.com.crt 12.1.11. Generating a New Key and Certificate In order to generate a new key and certificate pair the crypto-utils package must be installed on the system. To install it enter the following command as root: yum install crypto-utils This package provides a set of tools to generate and manage SSL certificates and private keys and includes genkey the Red Hat Keypair Generation utility that will guide you through the key generation process. Important If the server already has a valid certificate and you are replacing it with a new one specify a different serial number. This ensures that client browsers are notified of this change update to this new certificate as expected and do not fail to access the page. To create a new certificate with a custom serial number as root use the following command instead of genkey: openssl req -x509 -new -set_serial number -key hostname.key - out hostname.crt Note If there already is a key file for a particular host name in your system genkey will refuse to start. In this case remove the existing file using the following command as root: rm /etc/pki/tls/private/hostname.key To run the utility enter the genkey command as root followed by the appropriate host name for example penguin.example.com: genkey hostname To complete the key and certificate creation take the following steps: 1. Review the target locations in which the key and certificate will be stored. ⁠Chapt er 1 2 . Web Servers 175

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Figure 12.1. Running the genkey utility Use the Tab key to select the Next button and press Enter to proceed to the next screen. 2. Using the up and down arrow keys select a suitable key size. Note that while a larger key increases the security it also increases the response time of your server. The NIST recommends using 2048 bits. See NIST Special Publication 800-131A. Figure 12.2. Selecting the key siz e Once finished use the Tab key to select the Next button and press Enter to initiate the random bits generation process. Depending on the selected key size this may take some time. Syst em Administ rat ors Guide 176

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3. Decide whether you want to send a certificate request to a certificate authority. Figure 12.3. Generating a certificate request Use the Tab key to select Yes to compose a certificate request or No to generate a self- signed certificate. Then press Enter to confirm your choice. 4. Using the Spacebar key enable or disable the encryption of the private key. Figure 12.4 . Encrypting the private key ⁠Chapt er 1 2 . Web Servers 177

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Use the Tab key to select the Next button and press Enter to proceed to the next screen. 5. If you have enabled the private key encryption enter an adequate passphrase. Note that for security reasons it is not displayed as you type and it must be at least five characters long. Figure 12.5. Entering a passphrase Use the Tab key to select the Next button and press Enter to proceed to the next screen. Important Entering the correct passphrase is required in order for the server to start. If you lose it you will need to generate a new key and certificate. 6. Customize the certificate details. Syst em Administ rat ors Guide 178

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Figure 12.6 . Specifying certificate information Use the Tab key to select the Next button and press Enter to finish the key generation. 7. If you have previously enabled the certificate request generation you will be prompted to send it to a certificate authority. Figure 12.7. Instructions on how to send a certificate request Press Enter to return to a shell prompt. ⁠Chapt er 1 2 . Web Servers 179

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Once generated add the key and certificate locations to the /etc/httpd/conf.d/ssl.conf configuration file: SSLCertificateFile /etc/pki/tls/certs/hostname.crt SSLCertificateKeyFile /etc/pki/tls/private/hostname.key Finally restart the httpd service as described in Section 12.1.3.3 “Restarting the Service” so that the updated configuration is loaded. 12.1.12. Configure the Firewall for HT T P and HT T PS Using the Command Line Red Hat Enterprise Linux does not allow HTTP and HTTPS traffic by default. To enable the system to act as a web server make use of firewallds supported services to enable HTTP and HTTPS traffic to pass through the firewall as required. To enable HTTP using the command line issue the following command as root: firewall-cmd --add-service http success To enable HTTPS using the command line issue the following command as root: firewall-cmd --add-service https success Note that these changes will not persist after the next system start. To make permanent changes to the firewall repeat the commands adding the --permanent option. 12.1.12.1. Checking Net wo rk Access fo r Inco ming HT T PS and HT T PS Using t he Co mmand Line To check what services the firewall is configured to allow using the command line issue the following command as root: firewall-cmd --list-all public default active interfaces: em1 sources: services: dhcpv6-client ssh output truncated In this example taken from a default installation the firewall is enabled but HTTP and HTTPS have not been allowed to pass through. Once the HTTP and HTTP firewall services are enabled the services line will appear similar to the following: services: dhcpv6-client http https ssh For more information on enabling firewall services or opening and closing ports with firewalld see the Red Hat Enterprise Linux 7 Security Guide. 12.1.13. Additional Resources Syst em Administ rat ors Guide 180

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To learn more about the Apache HTTP Server see the following resources. Inst alled Do cument at io n httpd8 — The manual page for the httpd service containing the complete list of its command- line options. genkey1 — The manual page for genkey utility provided by the crypto-utils package. apachectl8 — The manual page for the Apache HTTP Server Control Interface. Inst allable Do cument at io n http://localhost/manual/ — The official documentation for the Apache HTTP Server with the full description of its directives and available modules. Note that in order to access this documentation you must have the httpd-manual package installed and the web server must be running. Before accessing the documentation issue the following commands as root: yum install httpd-manual apachectl graceful Online Do cument at io n http://httpd.apache.org/ — The official website for the Apache HTTP Server with documentation on all the directives and default modules. http://www.openssl.org/ — The OpenSSL home page containing further documentation frequently asked questions links to the mailing lists and other useful resources. ⁠Chapt er 1 2 . Web Servers 181

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Chapter 13. Mail Servers Red Hat Enterprise Linux offers many advanced applications to serve and access email. This chapter describes modern email protocols in use today and some of the programs designed to send and receive email. 13.1. Email Protocols Today email is delivered using a client/server architecture. An email message is created using a mail client program. This program then sends the message to a server. The server then forwards the message to the recipients email server where the message is then supplied to the recipients email client. To enable this process a variety of standard network protocols allow different machines often running different operating systems and using different email programs to send and receive email. The following protocols discussed are the most commonly used in the transfer of email. 13.1.1. Mail T ransport Protocols Mail delivery from a client application to the server and from an originating server to the destination server is handled by the Simple Mail Transfer Protocol SMTP. 13.1.1.1. SMT P The primary purpose of SMTP is to transfer email between mail servers. However it is critical for email clients as well. To send email the client sends the message to an outgoing mail server which in turn contacts the destination mail server for delivery. For this reason it is necessary to specify an SMTP server when configuring an email client. Under Red Hat Enterprise Linux a user can configure an SMTP server on the local machine to handle mail delivery. However it is also possible to configure remote SMTP servers for outgoing mail. One important point to make about the SMTP protocol is that it does not require authentication. This allows anyone on the Internet to send email to anyone else or even to large groups of people. It is this characteristic of SMTP that makes junk email or spam possible. Imposing relay restrictions limits random users on the Internet from sending email through your SMTP server to other servers on the internet. Servers that do not impose such restrictions are called open relay servers. Red Hat Enterprise Linux 7 provides the Postfix and Sendmail SMTP programs. 13.1.2. Mail Access Protocols There are two primary protocols used by email client applications to retrieve email from mail servers: the Post Office Protocol POP and the Internet Message Access Protocol IMAP. 13.1.2.1. POP The default POP server under Red Hat Enterprise Linux is Dovecot and is provided by the dovecot package. Syst em Administ rat ors Guide 182

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Note In order to use Dovecot first ensure the dovecot package is installed on your system by running as root: yum install dovecot For more information on installing packages with Yum see Section 8.2.4 “Installing Packages”. When using a POP server email messages are downloaded by email client applications. By default most POP email clients are automatically configured to delete the message on the email server after it has been successfully transferred however this setting usually can be changed. POP is fully compatible with important Internet messaging standards such as Multipurpose Internet Mail Extensions MIME which allow for email attachments. POP works best for users who have one system on which to read email. It also works well for users who do not have a persistent connection to the Internet or the network containing the mail server. Unfortunately for those with slow network connections POP requires client programs upon authentication to download the entire content of each message. This can take a long time if any messages have large attachments. The most current version of the standard POP protocol is POP3. There are however a variety of lesser-used POP protocol variants: APOP — POP3 with MD5 authentication. An encoded hash of the users password is sent from the email client to the server rather than sending an unencrypted password. KPOP — POP3 with Kerberos authentication. RPOP — POP3 with RPOP authentication. This uses a per-user ID similar to a password to authenticate POP requests. However this ID is not encrypted so RPOP is no more secure than standard POP. For added security it is possible to use Secure Socket Layer SSL encryption for client authentication and data transfer sessions. This can be enabled by using the pop3s service or by using the stunnel application. For more information on securing email communication see Section 13.5.1 “Securing Communication”. 13.1.2.2. IMAP The default IMAP server under Red Hat Enterprise Linux is Dovecot and is provided by the dovecot package. See Section 13.1.2.1 “POP” for information on how to install Dovecot. When using an IMAP mail server email messages remain on the server where users can read or delete them. IMAP also allows client applications to create rename or delete mail directories on the server to organize and store email. IMAP is particularly useful for users who access their email using multiple machines. The protocol is also convenient for users connecting to the mail server via a slow connection because only the email header information is downloaded for messages until opened saving bandwidth. The user also has the ability to delete messages without viewing or downloading them. ⁠Chapt er 1 3. Mail Servers 183

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For convenience IMAP client applications are capable of caching copies of messages locally so the user can browse previously read messages when not directly connected to the IMAP server. IMAP like POP is fully compatible with important Internet messaging standards such as MIME which allow for email attachments. For added security it is possible to use SSL encryption for client authentication and data transfer sessions. This can be enabled by using the imaps service or by using the stunnel program. For more information on securing email communication see Section 13.5.1 “Securing Communication”. Other free as well as commercial IMAP clients and servers are available many of which extend the IMAP protocol and provide additional functionality. 13.1.2.3. Do veco t The imap-login and pop3-login processes which implement the IMAP and POP3 protocols are spawned by the master dovecot daemon included in the dovecot package. The use of IMAP and POP is configured through the /etc/dovecot/dovecot.conf configuration file by default dovecot runs IMAP and POP3 together with their secure versions using SSL. To configure dovecot to use POP complete the following steps: 1. Edit the /etc/dovecot/dovecot.conf configuration file to make sure the protocols variable is uncommented remove the hash sign at the beginning of the line and contains the pop3 argument. For example: protocols imap pop3 lmtp When the protocols variable is left commented out dovecot will use the default values as described above. 2. Make the change operational for the current session by running the following command as root: systemctl restart dovecot 3. Make the change operational after the next reboot by running the command: systemctl enable dovecot Created symlink from /etc/systemd/system/multi- user.target.wants/dovecot.service to /usr/lib/systemd/system/dovecot.service. Note Please note that dovecot only reports that it started the IMAP server but also starts the POP3 server. Unlike SMTP both IMAP and POP3 require connecting clients to authenticate using a user name and password. By default passwords for both protocols are passed over the network unencrypted. To configure SSL on dovecot: Edit the /etc/dovecot/conf.d/10-ssl.conf configuration to make sure the ssl_protocols variable is uncommented and contains the SSLv2 SSLv3 arguments: Syst em Administ rat ors Guide 184

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ssl_protocols SSLv2 SSLv3 These values ensure that dovecot avoids SSL versions 2 and also 3 which are both known to be insecure. This is due to the vulnerability described in POODLE: SSLv3 vulnerability CVE-2014- 3566. See Resolution for POODLE SSL 3.0 vulnerability CVE-2014-3566 in Postfix and Dovecot for details. Edit the /etc/pki/dovecot/dovecot-openssl.cnf configuration file as you prefer. However in a typical installation this file does not require modification. Rename move or delete the files /etc/pki/dovecot/certs/dovecot.pem and /etc/pki/dovecot/private/dovecot.pem. Execute the /usr/libexec/dovecot/mkcert.sh script which creates the dovecot self signed certificates. These certificates are copied in the /etc/pki/dovecot/certs and /etc/pki/dovecot/private directories. To implement the changes restart dovecot by issuing the following command as root: systemctl restart dovecot More details on dovecot can be found online at http://www.dovecot.org. 13.2. Email Program Classifications In general all email applications fall into at least one of three classifications. Each classification plays a specific role in the process of moving and managing email messages. While most users are only aware of the specific email program they use to receive and send messages each one is important for ensuring that email arrives at the correct destination. 13.2.1. Mail T ransport Agent A Mail Transport Agent MTA transports email messages between hosts using SMTP. A message may involve several MTAs as it moves to its intended destination. While the delivery of messages between machines may seem rather straightforward the entire process of deciding if a particular MTA can or should accept a message for delivery is quite complicated. In addition due to problems from spam use of a particular MTA is usually restricted by the MTAs configuration or the access configuration for the network on which the MTA resides. Many modern email client programs can act as an MTA when sending email. However this action should not be confused with the role of a true MTA. The sole reason email client programs are capable of sending email like an MTA is because the host running the application does not have its own MTA. This is particularly true for email client programs on non-UNIX-based operating systems. However these client programs only send outbound messages to an MTA they are authorized to use and do not directly deliver the message to the intended recipients email server. Since Red Hat Enterprise Linux offers two MTAs Postfix and Sendmail email client programs are often not required to act as an MTA. Red Hat Enterprise Linux also includes a special purpose MTA called Fetchmail. For more information on Postfix Sendmail and Fetchmail see Section 13.3 “Mail Transport Agents”. 13.2.2. Mail Delivery Agent ⁠Chapt er 1 3. Mail Servers 185

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A Mail Delivery Agent MDA is invoked by the MTA to file incoming email in the proper users mailbox. In many cases the MDA is actually a Local Delivery Agent LDA such as mail or Procmail. Any program that actually handles a message for delivery to the point where it can be read by an email client application can be considered an MDA. For this reason some MTAs such as Sendmail and Postfix can fill the role of an MDA when they append new email messages to a local users mail spool file. In general MDAs do not transport messages between systems nor do they provide a user interface MDAs distribute and sort messages on the local machine for an email client application to access. 13.2.3. Mail User Agent A Mail User Agent MUA is synonymous with an email client application. An MUA is a program that at a minimum allows a user to read and compose email messages. Many MUAs are capable of retrieving messages via the POP or IMAP protocols setting up mailboxes to store messages and sending outbound messages to an MTA. MUAs may be graphical such as Evolution or have simple text-based interfaces such as Mutt. 13.3. Mail Transport Agents Red Hat Enterprise Linux 7 offers two primary MTAs: Postfix and Sendmail. Postfix is configured as the default MTA and Sendmail is considered deprecated. If required to switch the default MTA to Sendmail you can either uninstall Postfix or use the following command as root to switch to Sendmail: alternatives --config mta You can also use the following command to enable the desired service: systemctl enable service Similarly to disable the service type the following at a shell prompt: systemctl disable service For more information on how to manage system services in Red Hat Enterprise Linux 7 see Chapter 9 Managing Services with systemd. 13.3.1. Postfix Originally developed at IBM by security expert and programmer Wietse Venema Postfix is a Sendmail-compatible MTA that is designed to be secure fast and easy to configure. To improve security Postfix uses a modular design where small processes with limited privileges are launched by a master daemon. The smaller less privileged processes perform very specific tasks related to the various stages of mail delivery and run in a changed root environment to limit the effects of attacks. Configuring Postfix to accept network connections from hosts other than the local computer takes only a few minor changes in its configuration file. Yet for those with more complex needs Postfix provides a variety of configuration options as well as third party add-ons that make it a very versatile and full-featured MTA. Syst em Administ rat ors Guide 186

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The configuration files for Postfix are human readable and support upward of 250 directives. Unlike Sendmail no macro processing is required for changes to take effect and the majority of the most commonly used options are described in the heavily commented files. 13.3.1.1. T he Default Po st fix Inst allat io n The Postfix executable is postfix. This daemon launches all related processes needed to handle mail delivery. Postfix stores its configuration files in the /etc/postfix/ directory. The following is a list of the more commonly used files: access — Used for access control this file specifies which hosts are allowed to connect to Postfix. main.cf — The global Postfix configuration file. The majority of configuration options are specified in this file. master.cf — Specifies how Postfix interacts with various processes to accomplish mail delivery. transport — Maps email addresses to relay hosts. The aliases file can be found in the /etc directory. This file is shared between Postfix and Sendmail. It is a configurable list required by the mail protocol that describes user ID aliases. Important The default /etc/postfix/main.cf file does not allow Postfix to accept network connections from a host other than the local computer. For instructions on configuring Postfix as a server for other clients see Section 13.3.1.3 “Basic Postfix Configuration”. Restart the postfix service after changing any options in the configuration files under the /etc/postfix/ directory in order for those changes to take effect. To do so run the following command as root: systemctl restart postfix 13.3.1.2. Upgrading Fro m a Previo us Release The following settings in Red Hat Enterprise Linux 7 are different to previous releases: disable_vrfy_command no — This is disabled by default which is different to the default for Sendmail. If changed to yes it can prevent certain email address harvesting methods. allow_percent_hack yes — This is enabled by default. It allows removing characters in email addresses. The percent hack is an old workaround that allowed sender-controlled routing of email messages. DNS and mail routing are now much more reliable but Postfix continues to support the hack. To turn off percent rewriting set allow_percent_hack to no. smtpd_helo_required no — This is disabled by default as it is in Sendmail because it can prevent some applications from sending mail. It can be changed to yes to require clients to send the HELO or EHLO commands before attempting to send the MAIL FROM or ETRN commands. 13.3.1.3. Basic Po st fix Co nfigurat io n ⁠Chapt er 1 3. Mail Servers 187

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By default Postfix does not accept network connections from any host other than the local host. Perform the following steps as root to enable mail delivery for other hosts on the network: Edit the /etc/postfix/main.cf file with a text editor such as vi. Uncomment the mydomain line by removing the hash sign and replace domain.tld with the domain the mail server is servicing such as example.com. Uncomment the myorigin mydomain line. Uncomment the myhostname line and replace host.domain.tld with the host name for the machine. Uncomment the mydestination myhostname localhost.mydomain line. Uncomment the mynetworks line and replace 168.100.189.0/28 with a valid network setting for hosts that can connect to the server. Uncomment the inet_interfaces all line. Comment the inet_interfaces localhost line. Restart the postfix service. Once these steps are complete the host accepts outside emails for delivery. Postfix has a large assortment of configuration options. One of the best ways to learn how to configure Postfix is to read the comments within the /etc/postfix/main.cf configuration file. Additional resources including information about Postfix configuration SpamAssassin integration or detailed descriptions of the /etc/postfix/main.cf parameters are available online at http://www.postfix.org/. Important Due to the vulnerability described in POODLE: SSLv3 vulnerability CVE-2014-3566 Red Hat recommends disabling SSL and using only TLSv1.1 or TLSv1.2. See Resolution for POODLE SSL 3.0 vulnerability CVE-2014-3566 in Postfix and Dovecot for details. 13.3.1.4. Using Po st fix wit h LDAP Postfix can use an LDAP directory as a source for various lookup tables e.g.: aliases virtual canonical etc.. This allows LDAP to store hierarchical user information and Postfix to only be given the result of LDAP queries when needed. By not storing this information locally administrators can easily maintain it. 13.3.1.4 .1. The /etc/aliases lookup example The following is a basic example for using LDAP to look up the /etc/aliases file. Make sure your /etc/postfix/main.cf file contains the following: alias_maps hash:/etc/aliases ldap:/etc/postfix/ldap-aliases.cf Create a /etc/postfix/ldap-aliases.cf file if you do not have one already and make sure it contains the following: Syst em Administ rat ors Guide 188

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server_host ldap.example.com search_base dcexample dccom where ldap.example.com example and com are parameters that need to be replaced with specification of an existing available LDAP server. Note The /etc/postfix/ldap-aliases.cf file can specify various parameters including parameters that enable LDAP SSL and STARTTLS. For more information see the ldap_table5 man page. For more information on LDAP see OpenLDAP in the System-Level Authentication Guide. 13.3.2. Sendmail Sendmails core purpose like other MTAs is to safely transfer email among hosts usually using the SMTP protocol. Note that Sendmail is considered deprecated and users are encouraged to use Postfix when possible. See Section 13.3.1 “Postfix” for more information. 13.3.2.1. Purpo se and Limit at io ns It is important to be aware of what Sendmail is and what it can do as opposed to what it is not. In these days of monolithic applications that fulfill multiple roles Sendmail may seem like the only application needed to run an email server within an organization. Technically this is true as Sendmail can spool mail to each users directory and deliver outbound mail for users. However most users actually require much more than simple email delivery. Users usually want to interact with their email using an MUA that uses POP or IMAP to download their messages to their local machine. Or they may prefer a Web interface to gain access to their mailbox. These other applications can work in conjunction with Sendmail but they actually exist for different reasons and can operate separately from one another. It is beyond the scope of this section to go into all that Sendmail should or could be configured to do. With literally hundreds of different options and rule sets entire volumes have been dedicated to helping explain everything that can be done and how to fix things that go wrong. See the Section 13.6 “Additional Resources” for a list of Sendmail resources. This section reviews the files installed with Sendmail by default and reviews basic configuration changes including how to stop unwanted email spam and how to extend Sendmail with the Lightweight Directory Access Protocol LDAP. 13.3.2.2. T he Default Sendmail Inst allat io n In order to use Sendmail first ensure the sendmail package is installed on your system by running as root: yum install sendmail In order to configure Sendmail ensure the sendmail-cf package is installed on your system by running as root: yum install sendmail-cf ⁠Chapt er 1 3. Mail Servers 189

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For more information on installing packages with Yum see Section 8.2.4 “Installing Packages”. Before using Sendmail the default MTA has to be switched from Postfix. For more information how to switch the default MTA refer to Section 13.3 “Mail Transport Agents”. The Sendmail executable is sendmail. Sendmails lengthy and detailed configuration file is /etc/mail/sendmail.cf. Avoid editing the sendmail.cf file directly. To make configuration changes to Sendmail edit the /etc/mail/sendmail.mc file back up the original /etc/mail/sendmail.cf file and use the following alternatives to generate a new configuration file: Use the included makefile in /etc/mail/ to create a new /etc/mail/sendmail.cf configuration file: make all -C /etc/mail/ All other generated files in /etc/mail db files will be regenerated if needed. The old makemap commands are still usable. The make command is automatically used whenever you start or restart the sendmail service. More information on configuring Sendmail can be found in Section 13.3.2.3 “Common Sendmail Configuration Changes”. Various Sendmail configuration files are installed in the /etc/mail/ directory including: access — Specifies which systems can use Sendmail for outbound email. domaintable — Specifies domain name mapping. local-host-names — Specifies aliases for the host. mailertable — Specifies instructions that override routing for particular domains. virtusertable — Specifies a domain-specific form of aliasing allowing multiple virtual domains to be hosted on one machine. Several of the configuration files in the /etc/mail/ directory such as access domaintable mailertable and virtusertable must actually store their information in database files before Sendmail can use any configuration changes. To include any changes made to these configurations in their database files run the following commands as root: cd /etc/mail/ make all This will update virtusertable.db access.db domaintable.db mailertable.db sendmail.cf and submit.cf. To update all the database files listed above and to update a custom database file use a command in the following format: make name.db all where name represents the name of the custom database file to be updated. To update a single database use a command in the following format: make name.db Syst em Administ rat ors Guide 190

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where name.db represents the name of the database file to be updated. You may also restart the sendmail service for the changes to take effect by running: systemctl restart sendmail For example to have all emails addressed to the example.com domain delivered to bobother- example.com add the following line to the virtusertable file: example.com bobother-example.com To finalize the change the virtusertable.db file must be updated: make virtusertable.db all Using the all option will result in the virtusertable.db and access.db being updated at the same time. 13.3.2.3. Co mmo n Sendmail Co nfigurat io n Changes When altering the Sendmail configuration file it is best not to edit an existing file but to generate an entirely new /etc/mail/sendmail.cf file. Warning Before replacing or making any changes to the sendmail.cf file create a backup copy. To add the desired functionality to Sendmail edit the /etc/mail/sendmail.mc file as root. Once you are finished restart the sendmail service and if the m4 package is installed the m4 macro processor will automatically generate a new sendmail.cf configuration file: systemctl restart sendmail Important The default sendmail.cf file does not allow Sendmail to accept network connections from any host other than the local computer. To configure Sendmail as a server for other clients edit the /etc/mail/sendmail.mc file and either change the address specified in the Addr option of the DAEMON_OPTIONS directive from 127.0.0.1 to the IP address of an active network device or comment out the DAEMON_OPTIONS directive all together by placing dnl at the beginning of the line. When finished regenerate /etc/mail/sendmail.cf by restarting the service: systemctl restart sendmail ⁠Chapt er 1 3. Mail Servers 191

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The default configuration in Red Hat Enterprise Linux works for most SMTP-only sites. However it does not work for UUCP UNIX-to-UNIX Copy Protocol sites. If using UUCP mail transfers the /etc/mail/sendmail.mc file must be reconfigured and a new /etc/mail/sendmail.cf file must be generated. Consult the /usr/share/sendmail-cf/README file before editing any files in the directories under the /usr/share/sendmail-cf/ directory as they can affect the future configuration of the /etc/mail/sendmail.cf file. 13.3.2.4. Masquerading One common Sendmail configuration is to have a single machine act as a mail gateway for all machines on the network. For example a company may want to have a machine called mail.example.com that handles all of their email and assigns a consistent return address to all outgoing mail. In this situation the Sendmail server must masquerade the machine names on the company network so that their return address is userexample.com instead of userhost.example.com. To do this add the following lines to /etc/mail/sendmail.mc: FEATUREalways_add_domaindnl FEATURE`masquerade_entire_domaindnl FEATURE`masquerade_envelopednl FEATURE`allmasqueradednl MASQUERADE_AS`example.com.dnl MASQUERADE_DOMAIN`example.com.dnl MASQUERADE_ASexample.comdnl After generating a new sendmail.cf file using the m4 macro processor this configuration makes all mail from inside the network appear as if it were sent from example.com. Note that administrators of mail servers DNS and DHCP servers as well as any provisioning applications should agree on the host name format used in an organization. See the Red Hat Enterprise Linux 7 Networking Guide for more information on recommended naming practices. 13.3.2.5. St o pping Spam Email spam can be defined as unnecessary and unwanted email received by a user who never requested the communication. It is a disruptive costly and widespread abuse of Internet communication standards. Sendmail makes it relatively easy to block new spamming techniques being employed to send junk email. It even blocks many of the more usual spamming methods by default. Main anti-spam features available in sendmail are header checks relaying denial default from version 8.9 access database and sender information checks. For example forwarding of SMTP messages also called relaying has been disabled by default since Sendmail version 8.9. Before this change occurred Sendmail directed the mail host x.edu to accept messages from one party y.com and sent them to a different party z.net. Now however Sendmail must be configured to permit any domain to relay mail through the server. To configure relay domains edit the /etc/mail/relay-domains file and restart Sendmail systemctl restart sendmail Syst em Administ rat ors Guide 192

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However users can also be sent spam from from servers on the Internet. In these instances Sendmails access control features available through the /etc/mail/access file can be used to prevent connections from unwanted hosts. The following example illustrates how this file can be used to both block and specifically allow access to the Sendmail server: badspammer.com ERROR:550 "Go away and do not spam us anymore" tux.badspammer.com OK 10.0 RELAY This example shows that any email sent from badspammer.com is blocked with a 550 RFC-821 compliant error code with a message sent back. Email sent from the tux.badspammer.com sub- domain is accepted. The last line shows that any email sent from the 10.0.. network can be relayed through the mail server. Because the /etc/mail/access.db file is a database use the makemap command to update any changes. Do this using the following command as root: makemap hash /etc/mail/access /etc/mail/access Message header analysis allows you to reject mail based on header contents. SMTP servers store information about an emails journey in the message header. As the message travels from one MTA to another each puts in a Received header above all the other Received headers. It is important to note that this information may be altered by spammers. The above examples only represent a small part of what Sendmail can do in terms of allowing or blocking access. See the /usr/share/sendmail-cf/README file for more information and examples. Since Sendmail calls the Procmail MDA when delivering mail it is also possible to use a spam filtering program such as SpamAssassin to identify and file spam for users. See Section 13.4.2.6 “Spam Filters” for more information about using SpamAssassin. 13.3.2.6. Using Sendmail wit h LDAP Using LDAP is a very quick and powerful way to find specific information about a particular user from a much larger group. For example an LDAP server can be used to look up a particular email address from a common corporate directory by the users last name. In this kind of implementation LDAP is largely separate from Sendmail with LDAP storing the hierarchical user information and Sendmail only being given the result of LDAP queries in pre-addressed email messages. However Sendmail supports a much greater integration with LDAP where it uses LDAP to replace separately maintained files such as /etc/aliases and /etc/mail/virtusertables on different mail servers that work together to support a medium- to enterprise-level organization. In short LDAP abstracts the mail routing level from Sendmail and its separate configuration files to a powerful LDAP cluster that can be leveraged by many different applications. The current version of Sendmail contains support for LDAP. To extend the Sendmail server using LDAP first get an LDAP server such as OpenLDAP running and properly configured. Then edit the /etc/mail/sendmail.mc to include the following: LDAPROUTE_DOMAINyourdomain.comdnl FEATUREldap_routingdnl ⁠Chapt er 1 3. Mail Servers 193

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Note This is only for a very basic configuration of Sendmail with LDAP. The configuration can differ greatly from this depending on the implementation of LDAP especially when configuring several Sendmail machines to use a common LDAP server. Consult /usr/share/sendmail-cf/README for detailed LDAP routing configuration instructions and examples. Next recreate the /etc/mail/sendmail.cf file by running the m4 macro processor and again restarting Sendmail. See Section 13.3.2.3 “Common Sendmail Configuration Changes” for instructions. For more information on LDAP see OpenLDAP in the System-Level Authentication Guide. 13.3.3. Fetchmail Fetchmail is an MTA which retrieves email from remote servers and delivers it to the local MTA. Many users appreciate the ability to separate the process of downloading their messages located on a remote server from the process of reading and organizing their email in an MUA. Designed with the needs of dial-up users in mind Fetchmail connects and quickly downloads all of the email messages to the mail spool file using any number of protocols including POP3 and IMAP. It can even forward email messages to an SMTP server if necessary. Note In order to use Fetchmail first ensure the fetchmail package is installed on your system by running as root: yum install fetchmail For more information on installing packages with Yum see Section 8.2.4 “Installing Packages”. Fetchmail is configured for each user through the use of a .fetchmailrc file in the users home directory. If it does not already exist create the .fetchmailrc file in your home directory Using preferences in the .fetchmailrc file Fetchmail checks for email on a remote server and downloads it. It then delivers it to port 25 on the local machine using the local MTA to place the email in the correct users spool file. If Procmail is available it is launched to filter the email and place it in a mailbox so that it can be read by an MUA. 13.3.3.1. Fet chmail Co nfigurat io n Opt io ns Although it is possible to pass all necessary options on the command line to check for email on a remote server when executing Fetchmail using a .fetchmailrc file is much easier. Place any desired configuration options in the .fetchmailrc file for those options to be used each time the fetchmail command is issued. It is possible to override these at the time Fetchmail is run by specifying that option on the command line. Syst em Administ rat ors Guide 194

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A users .fetchmailrc file contains three classes of configuration options: global options — Gives Fetchmail instructions that control the operation of the program or provide settings for every connection that checks for email. server options — Specifies necessary information about the server being polled such as the host name as well as preferences for specific email servers such as the port to check or number of seconds to wait before timing out. These options affect every user using that server. user options — Contains information such as user name and password necessary to authenticate and check for email using a specified email server. Global options appear at the top of the .fetchmailrc file followed by one or more server options each of which designate a different email server that Fetchmail should check. User options follow server options for each user account checking that email server. Like server options multiple user options may be specified for use with a particular server as well as to check multiple email accounts on the same server. Server options are called into service in the .fetchmailrc file by the use of a special option verb poll or skip that precedes any of the server information. The poll action tells Fetchmail to use this server option when it is run which checks for email using the specified user options. Any server options after a skip action however are not checked unless this servers host name is specified when Fetchmail is invoked. The skip option is useful when testing configurations in the .fetchmailrc file because it only checks skipped servers when specifically invoked and does not affect any currently working configurations. The following is an example of a .fetchmailrc file: set postmaster "user1" set bouncemail poll pop.domain.com proto pop3 user user1 there with password secret is user1 here poll mail.domain2.com user user5 there with password secret2 is user1 here user user7 there with password secret3 is user1 here In this example the global options specify that the user is sent email as a last resort postmaster option and all email errors are sent to the postmaster instead of the sender bouncemail option. The set action tells Fetchmail that this line contains a global option. Then two email servers are specified one set to check using POP3 the other for trying various protocols to find one that works. Two users are checked using the second server option but all email found for any user is sent to user1s mail spool. This allows multiple mailboxes to be checked on multiple servers while appearing in a single MUA inbox. Each users specific information begins with the user action. Note Users are not required to place their password in the .fetchmailrc file. Omitting the with password password section causes Fetchmail to ask for a password when it is launched. Fetchmail has numerous global server and local options. Many of these options are rarely used or only apply to very specific situations. The fetchmail man page explains each option in detail but the most common ones are listed in the following three sections. ⁠Chapt er 1 3. Mail Servers 195

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13.3.3.2. Glo bal Opt io ns Each global option should be placed on a single line after a set action. daemon seconds — Specifies daemon-mode where Fetchmail stays in the background. Replace seconds with the number of seconds Fetchmail is to wait before polling the server. postmaster — Specifies a local user to send mail to in case of delivery problems. syslog — Specifies the log file for errors and status messages. By default this is /var/log/maillog. 13.3.3.3. Server Opt io ns Server options must be placed on their own line in .fetchmailrc after a poll or skip action. auth auth-type — Replace auth-type with the type of authentication to be used. By default password authentication is used but some protocols support other types of authentication including kerberos_v5 kerberos_v4 and ssh. If the any authentication type is used Fetchmail first tries methods that do not require a password then methods that mask the password and finally attempts to send the password unencrypted to authenticate to the server. interval number — Polls the specified server every number of times that it checks for email on all configured servers. This option is generally used for email servers where the user rarely receives messages. port port-number — Replace port-number with the port number. This value overrides the default port number for the specified protocol. proto protocol — Replace protocol with the protocol such as pop3 or imap to use when checking for messages on the server. timeout seconds — Replace seconds with the number of seconds of server inactivity after which Fetchmail gives up on a connection attempt. If this value is not set a default of 300 seconds is used. 13.3.3.4. User Opt io ns User options may be placed on their own lines beneath a server option or on the same line as the server option. In either case the defined options must follow the user option defined below. fetchall — Orders Fetchmail to download all messages in the queue including messages that have already been viewed. By default Fetchmail only pulls down new messages. fetchlimit number — Replace number with the number of messages to be retrieved before stopping. flush — Deletes all previously viewed messages in the queue before retrieving new messages. limit max-number-bytes — Replace max-number-bytes with the maximum size in bytes that messages are allowed to be when retrieved by Fetchmail. This option is useful with slow network links when a large message takes too long to download. password password — Replace password with the users password. preconnect "command" — Replace command with a command to be executed before retrieving messages for the user. Syst em Administ rat ors Guide 196

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postconnect "command" — Replace command with a command to be executed after retrieving messages for the user. ssl — Activates SSL encryption. At the time of writing the default action is to use the best available from SSL2 SSL3 SSL23 TLS1 TLS1.1 and TLS1.2. Note that SSL2 is considered obsolete and due to the POODLE: SSLv3 vulnerability CVE-2014-3566 SSLv3 should not be used. However there is no way to force the use of TLS1 or newer therefore ensure the mail server being connected to is configured not to use SSLv2 and SSLv3. Use stunnel where the server cannot be configured not to use SSLv2 and SSLv3. sslproto — Defines allowed SSL or TLS protocols. Possible values are SSL2 SSL3 SSL23 and TLS1. The default value if sslproto is omitted unset or set to an invalid value is SSL23. The default action is to use the best from SSLv2 SSLv3 TLSv1 TLS1.1 and TLS1.2. Note that setting any other value for SSL or TLS will disable all the other protocols. Due to the POODLE: SSLv3 vulnerability CVE-2014-3566 it is recommend to omit this option or set it to SSLv23 and configure the corresponding mail server not to use SSLv2 and SSLv3. Use stunnel where the server cannot be configured not to use SSLv2 and SSLv3. user "username" — Replace username with the username used by Fetchmail to retrieve messages. This option must precede all other user options. 13.3.3.5. Fet chmail Co mmand Opt io ns Most Fetchmail options used on the command line when executing the fetchmail command mirror the .fetchmailrc configuration options. In this way Fetchmail may be used with or without a configuration file. These options are not used on the command line by most users because it is easier to leave them in the .fetchmailrc file. There may be times when it is desirable to run the fetchmail command with other options for a particular purpose. It is possible to issue command options to temporarily override a .fetchmailrc setting that is causing an error as any options specified at the command line override configuration file options. 13.3.3.6. Info rmat io nal o r Debugging Opt io ns Certain options used after the fetchmail command can supply important information. --configdump — Displays every possible option based on information from .fetchmailrc and Fetchmail defaults. No email is retrieved for any users when using this option. -s — Executes Fetchmail in silent mode preventing any messages other than errors from appearing after the fetchmail command. -v — Executes Fetchmail in verbose mode displaying every communication between Fetchmail and remote email servers. -V — Displays detailed version information lists its global options and shows settings to be used with each user including the email protocol and authentication method. No email is retrieved for any users when using this option. 13.3.3.7. Special Opt io ns These options are occasionally useful for overriding defaults often found in the .fetchmailrc file. -a — Fetchmail downloads all messages from the remote email server whether new or previously viewed. By default Fetchmail only downloads new messages. ⁠Chapt er 1 3. Mail Servers 197

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-k — Fetchmail leaves the messages on the remote email server after downloading them. This option overrides the default behavior of deleting messages after downloading them. -l max-number-bytes — Fetchmail does not download any messages over a particular size and leaves them on the remote email server. --quit — Quits the Fetchmail daemon process. More commands and .fetchmailrc options can be found in the fetchmail man page. 13.3.4 . Mail T ransport Agent MT A Configuration A Mail Transport Agent MTA is essential for sending email. A Mail User Agent MUA such as Evolution or Mutt is used to read and compose email. When a user sends an email from an MUA the message is handed off to the MTA which sends the message through a series of MTAs until it reaches its destination. Even if a user does not plan to send email from the system some automated tasks or system programs might use the mail command to send email containing log messages to the root user of the local system. Red Hat Enterprise Linux 7 provides two MTAs: Postfix and Sendmail. If both are installed Postfix is the default MTA. Note that Sendmail is considered deprecated in Red Hat Enterprise Linux 7. 13.4. Mail Delivery Agents Red Hat Enterprise Linux includes two primary MDAs Procmail and mail. Both of the applications are considered LDAs and both move email from the MTAs spool file into the users mailbox. However Procmail provides a robust filtering system. This section details only Procmail. For information on the mail command consult its man page man mail. Procmail delivers and filters email as it is placed in the mail spool file of the localhost. It is powerful gentle on system resources and widely used. Procmail can play a critical role in delivering email to be read by email client applications. Procmail can be invoked in several different ways. Whenever an MTA places an email into the mail spool file Procmail is launched. Procmail then filters and files the email for the MUA and quits. Alternatively the MUA can be configured to execute Procmail any time a message is received so that messages are moved into their correct mailboxes. By default the presence of /etc/procmailrc or of a /.procmailrc file also called an rc file in the users home directory invokes Procmail whenever an MTA receives a new message. By default no system-wide rc files exist in the /etc directory and no .procmailrc files exist in any users home directory. Therefore to use Procmail each user must construct a .procmailrc file with specific environment variables and rules. Whether Procmail acts upon an email message depends upon whether the message matches a specified set of conditions or recipes in the rc file. If a message matches a recipe then the email is placed in a specified file is deleted or is otherwise processed. When Procmail starts it reads the email message and separates the body from the header information. Next Procmail looks for a /etc/procmailrc file and rc files in the /etc/procmailrcs/ directory for default system-wide Procmail environmental variables and recipes. Procmail then searches for a .procmailrc file in the users home directory. Many users Syst em Administ rat ors Guide 198

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also create additional rc files for Procmail that are referred to within the .procmailrc file in their home directory. 13.4 .1. Procmail Configuration The Procmail configuration file contains important environmental variables. These variables specify things such as which messages to sort and what to do with the messages that do not match any recipes. These environmental variables usually appear at the beginning of the /.procmailrc file in the following format: env-variable"value" In this example env-variable is the name of the variable and value defines the variable. There are many environment variables not used by most Procmail users and many of the more important environment variables are already defined by a default value. Most of the time the following variables are used: DEFAULT — Sets the default mailbox where messages that do not match any recipes are placed. The default DEFAULT value is the same as ORGMAIL. INCLUDERC — Specifies additional rc files containing more recipes for messages to be checked against. This breaks up the Procmail recipe lists into individual files that fulfill different roles such as blocking spam and managing email lists that can then be turned off or on by using comment characters in the users /.procmailrc file. For example lines in a users /.procmailrc file may look like this: MAILDIRHOME/Msgs INCLUDERCMAILDIR/lists.rc INCLUDERCMAILDIR/spam.rc To turn off Procmail filtering of email lists but leaving spam control in place comment out the first INCLUDERC line with a hash sign . Note that it uses paths relative to the current directory. LOCKSLEEP — Sets the amount of time in seconds between attempts by Procmail to use a particular lockfile. The default is 8 seconds. LOCKTIMEOUT — Sets the amount of time in seconds that must pass after a lockfile was last modified before Procmail assumes that the lockfile is old and can be deleted. The default is 1024 seconds. LOGFILE — The file to which any Procmail information or error messages are written. MAILDIR — Sets the current working directory for Procmail. If set all other Procmail paths are relative to this directory. ORGMAIL — Specifies the original mailbox or another place to put the messages if they cannot be placed in the default or recipe-required location. By default a value of /var/spool/mail/LOGNAME is used. SUSPEND — Sets the amount of time in seconds that Procmail pauses if a necessary resource such as swap space is not available. ⁠Chapt er 1 3. Mail Servers 199

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SWITCHRC — Allows a user to specify an external file containing additional Procmail recipes much like the INCLUDERC option except that recipe checking is actually stopped on the referring configuration file and only the recipes on the SWITCHRC-specified file are used. VERBOSE — Causes Procmail to log more information. This option is useful for debugging. Other important environmental variables are pulled from the shell such as LOGNAME the login name HOME the location of the home directory and SHELL the default shell. A comprehensive explanation of all environments variables and their default values is available in the procmailrc man page. 13.4 .2. Procmail Recipes New users often find the construction of recipes the most difficult part of learning to use Procmail. This difficulty is often attributed to recipes matching messages by using regular expressions which are used to specify qualifications for string matching. However regular expressions are not very difficult to construct and even less difficult to understand when read. Additionally the consistency of the way Procmail recipes are written regardless of regular expressions makes it easy to learn by example. To see example Procmail recipes see Section 13.4.2.5 “Recipe Examples”. Procmail recipes take the following form: :0 flags : lockfile-name condition_1_special-condition-character condition_1_regular_expression condition_2_special-condition-character condition- 2_regular_expression condition_N_special-condition-character condition- N_regular_expression special-action-character action-to-perform The first two characters in a Procmail recipe are a colon and a zero. Various flags can be placed after the zero to control how Procmail processes the recipe. A colon after the flags section specifies that a lockfile is created for this message. If a lockfile is created the name can be specified by replacing lockfile-name. A recipe can contain several conditions to match against the message. If it has no conditions every message matches the recipe. Regular expressions are placed in some conditions to facilitate message matching. If multiple conditions are used they must all match for the action to be performed. Conditions are checked based on the flags set in the recipes first line. Optional special characters placed after the asterisk character can further control the condition. The action-to-perform argument specifies the action taken when the message matches one of the conditions. There can only be one action per recipe. In many cases the name of a mailbox is used here to direct matching messages into that file effectively sorting the email. Special action characters may also be used before the action is specified. See Section 13.4.2.4 “Special Conditions and Actions” for more information. 13.4.2.1. Delivering vs. No n-Delivering Recipes The action used if the recipe matches a particular message determines whether it is considered a delivering or non-delivering recipe. A delivering recipe contains an action that writes the message to a file sends the message to another program or forwards the message to another email address. A non-delivering recipe covers any other actions such as a nesting block. A nesting block is a set of Syst em Administ rat ors Guide 200

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actions contained in braces that are performed on messages which match the recipes conditions. Nesting blocks can be nested inside one another providing greater control for identifying and performing actions on messages. When messages match a delivering recipe Procmail performs the specified action and stops comparing the message against any other recipes. Messages that match non-delivering recipes continue to be compared against other recipes. 13.4.2.2. Flags Flags are essential to determine how or if a recipes conditions are compared to a message. The egrep utility is used internally for matching of the conditions. The following flags are commonly used: A — Specifies that this recipe is only used if the previous recipe without an A or a flag also matched this message. a — Specifies that this recipe is only used if the previous recipe with an A or a flag also matched this message and was successfully completed. B — Parses the body of the message and looks for matching conditions. b — Uses the body in any resulting action such as writing the message to a file or forwarding it. This is the default behavior. c — Generates a carbon copy of the email. This is useful with delivering recipes since the required action can be performed on the message and a copy of the message can continue being processed in the rc files. D — Makes the egrep comparison case-sensitive. By default the comparison process is not case-sensitive. E — While similar to the A flag the conditions in the recipe are only compared to the message if the immediately preceding recipe without an E flag did not match. This is comparable to an else action. e — The recipe is compared to the message only if the action specified in the immediately preceding recipe fails. f — Uses the pipe as a filter. H — Parses the header of the message and looks for matching conditions. This is the default behavior. h — Uses the header in a resulting action. This is the default behavior. w — Tells Procmail to wait for the specified filter or program to finish and reports whether or not it was successful before considering the message filtered. W — Is identical to w except that "Program failure" messages are suppressed. For a detailed list of additional flags see the procmailrc man page. 13.4.2.3. Specifying a Lo cal Lo ckfile Lockfiles are very useful with Procmail to ensure that more than one process does not try to alter a message simultaneously. Specify a local lockfile by placing a colon : after any flags on a recipes first line. This creates a local lockfile based on the destination file name plus whatever has been set in the LOCKEXT global environment variable. ⁠Chapt er 1 3. Mail Servers 201

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Alternatively specify the name of the local lockfile to be used with this recipe after the colon. 13.4.2.4. Special Co ndit io ns and Act io ns Special characters used before Procmail recipe conditions and actions change the way they are interpreted. The following characters may be used after the asterisk character at the beginning of a recipes condition line: — In the condition line this character inverts the condition causing a match to occur only if the condition does not match the message. — Checks if the message is under a specified number of bytes. — Checks if the message is over a specified number of bytes. The following characters are used to perform special actions: — In the action line this character tells Procmail to forward the message to the specified email addresses. — Refers to a variable set earlier in the rc file. This is often used to set a common mailbox that is referred to by various recipes. | — Starts a specified program to process the message. and — Constructs a nesting block used to contain additional recipes to apply to matching messages. If no special character is used at the beginning of the action line Procmail assumes that the action line is specifying the mailbox in which to write the message. 13.4.2.5. Recipe Examples Procmail is an extremely flexible program but as a result of this flexibility composing Procmail recipes from scratch can be difficult for new users. The best way to develop the skills to build Procmail recipe conditions stems from a strong understanding of regular expressions combined with looking at many examples built by others. A thorough explanation of regular expressions is beyond the scope of this section. The structure of Procmail recipes and useful sample Procmail recipes can be found at various places on the Internet. The proper use and adaptation of regular expressions can be derived by viewing these recipe examples. In addition introductory information about basic regular expression rules can be found in the grep1 man page. The following simple examples demonstrate the basic structure of Procmail recipes and can provide the foundation for more intricate constructions. A basic recipe may not even contain conditions as is illustrated in the following example: :0: new-mail.spool The first line specifies that a local lockfile is to be created but does not specify a name so Procmail uses the destination file name and appends the value specified in the LOCKEXT environment variable. No condition is specified so every message matches this recipe and is placed in the single spool file called new-mail.spool located within the directory specified by the MAILDIR Syst em Administ rat ors Guide 202

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environment variable. An MUA can then view messages in this file. A basic recipe such as this can be placed at the end of all rc files to direct messages to a default location. The following example matched messages from a specific email address and throws them away. :0 From: spammerdomain.com /dev/null With this example any messages sent by spammerdomain.com are sent to the /dev/null device deleting them. Warning Be certain that rules are working as intended before sending messages to /dev/null for permanent deletion. If a recipe inadvertently catches unintended messages and those messages disappear it becomes difficult to troubleshoot the rule. A better solution is to point the recipes action to a special mailbox which can be checked from time to time to look for false positives. Once satisfied that no messages are accidentally being matched delete the mailbox and direct the action to send the messages to /dev/null. The following recipe grabs email sent from a particular mailing list and places it in a specified folder. :0: From|Cc|To.tux-lug tuxlug Any messages sent from the tux-lugdomain.com mailing list are placed in the tuxlug mailbox automatically for the MUA. Note that the condition in this example matches the message if it has the mailing lists email address on the From Cc or To lines. Consult the many Procmail online resources available in Section 13.6 “Additional Resources” for more detailed and powerful recipes. 13.4.2.6. Spam Filt ers Because it is called by Sendmail Postfix and Fetchmail upon receiving new emails Procmail can be used as a powerful tool for combating spam. This is particularly true when Procmail is used in conjunction with SpamAssassin. When used together these two applications can quickly identify spam emails and sort or destroy them. SpamAssassin uses header analysis text analysis blacklists a spam-tracking database and self- learning Bayesian spam analysis to quickly and accurately identify and tag spam. ⁠Chapt er 1 3. Mail Servers 203

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Note In order to use SpamAssassin first ensure the spamassassin package is installed on your system by running as root: yum install spamassassin For more information on installing packages with Yum see Section 8.2.4 “Installing Packages”. The easiest way for a local user to use SpamAssassin is to place the following line near the top of the /.procmailrc file: INCLUDERC/etc/mail/spamassassin/spamassassin-default.rc The /etc/mail/spamassassin/spamassassin-default.rc contains a simple Procmail rule that activates SpamAssassin for all incoming email. If an email is determined to be spam it is tagged in the header as such and the title is prepended with the following pattern: SPAM The message body of the email is also prepended with a running tally of what elements caused it to be diagnosed as spam. To file email tagged as spam a rule similar to the following can be used: :0 Hw X-Spam-Status: Yes spam This rule files all email tagged in the header as spam into a mailbox called spam. Since SpamAssassin is a Perl script it may be necessary on busy servers to use the binary SpamAssassin daemon spamd and the client application spamc. Configuring SpamAssassin this way however requires root access to the host. To start the spamd daemon type the following command: systemctl start spamassassin To start the SpamAssassin daemon when the system is booted run: systemctl enable spamassassin.service See Chapter 9 Managing Services with systemd for more information about starting and stopping services. To configure Procmail to use the SpamAssassin client application instead of the Perl script place the following line near the top of the /.procmailrc file. For a system-wide configuration place it in /etc/procmailrc: INCLUDERC/etc/mail/spamassassin/spamassassin-spamc.rc Syst em Administ rat ors Guide 204

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13.5. Mail User Agents Red Hat Enterprise Linux offers a variety of email programs both graphical email client programs such as Evolution and text-based email programs such as mutt. The remainder of this section focuses on securing communication between a client and a server. 13.5.1. Securing Communication Popular MUAs included with Red Hat Enterprise Linux such as Evolution and Mutt offer SSL- encrypted email sessions. Like any other service that flows over a network unencrypted important email information such as user names passwords and entire messages may be intercepted and viewed by users on the network. Additionally since the standard POP and IMAP protocols pass authentication information unencrypted it is possible for an attacker to gain access to user accounts by collecting user names and passwords as they are passed over the network. 13.5.1.1. Secure Email Client s Most Linux MUAs designed to check email on remote servers support SSL encryption. To use SSL when retrieving email it must be enabled on both the email client and the server. SSL is easy to enable on the client-side often done with the click of a button in the MUAs configuration window or via an option in the MUAs configuration file. Secure IMAP and POP have known port numbers 993 and 995 respectively that the MUA uses to authenticate and download messages. 13.5.1.2. Securing Email Client Co mmunicat io ns Offering SSL encryption to IMAP and POP users on the email server is a simple matter. First create an SSL certificate. This can be done in two ways: by applying to a Certificate Authority CA for an SSL certificate or by creating a self-signed certificate. Warning Self-signed certificates should be used for testing purposes only. Any server used in a production environment should use an SSL certificate signed by a CA. To create a self-signed SSL certificate for IMAP or POP change to the /etc/pki/dovecot/ directory edit the certificate parameters in the /etc/pki/dovecot/dovecot-openssl.cnf configuration file as you prefer and type the following commands as root: dovecot rm -f certs/dovecot.pem private/dovecot.pem dovecot /usr/libexec/dovecot/mkcert.sh Once finished make sure you have the following configurations in your /etc/dovecot/conf.d/10-ssl.conf file: ssl_cert /etc/pki/dovecot/certs/dovecot.pem ssl_key /etc/pki/dovecot/private/dovecot.pem ⁠Chapt er 1 3. Mail Servers 205

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Issue the following command to restart the dovecot daemon: systemctl restart dovecot Alternatively the stunnel command can be used as an encryption wrapper around the standard non-secure connections to IMAP or POP services. The stunnel utility uses external OpenSSL libraries included with Red Hat Enterprise Linux to provide strong cryptography and to protect the network connections. It is recommended to apply to a CA to obtain an SSL certificate but it is also possible to create a self-signed certificate. See Using stunnel in the Red Hat Enterprise Linux 7 Security Guide for instructions on how to install stunnel and create its basic configuration. To configure stunnel as a wrapper for IMAPS and POP3S add the following lines to the /etc/stunnel/stunnel.conf configuration file: pop3s accept 995 connect 110 imaps accept 993 connect 143 The Security Guide also explains how to start and stop stunnel. Once you start it it is possible to use an IMAP or a POP email client and connect to the email server using SSL encryption. 13.6. Additional Resources The following is a list of additional documentation about email applications. 13.6.1. Installed Documentation Information on configuring Sendmail is included with the sendmail and sendmail-cf packages. /usr/share/sendmail-cf/README — Contains information on the m4 macro processor file locations for Sendmail supported mailers how to access enhanced features and more. In addition the sendmail and aliases man pages contain helpful information covering various Sendmail options and the proper configuration of the Sendmail /etc/mail/aliases file. /usr/share/doc/postfix-version-number/ — Contains a large amount of information on how to configure Postfix. Replace version-number with the version number of Postfix. /usr/share/doc/fetchmail-version-number/ — Contains a full list of Fetchmail features in the FEATURES file and an introductory FAQ document. Replace version-number with the version number of Fetchmail. /usr/share/doc/procmail-version-number/ — Contains a README file that provides an overview of Procmail a FEATURES file that explores every program feature and an FAQ file with answers to many common configuration questions. Replace version-number with the version number of Procmail. When learning how Procmail works and creating new recipes the following Procmail man pages are invaluable: Syst em Administ rat ors Guide 206

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procmail — Provides an overview of how Procmail works and the steps involved with filtering email. procmailrc — Explains the rc file format used to construct recipes. procmailex — Gives a number of useful real-world examples of Procmail recipes. procmailsc — Explains the weighted scoring technique used by Procmail to match a particular recipe to a message. /usr/share/doc/spamassassin-version-number/ — Contains a large amount of information pertaining to SpamAssassin. Replace version-number with the version number of the spamassassin package. 13.6.2. Online Documentation How to configure postfix with TLS — A Red Hat Knowledgebase article that describes configuring postfix to use TLS. How to configure a Sendmail Smart Host — A Red Hat Knowledgebase solution that describes configuring a sendmail Smart Host. http://www.sendmail.org/ — Offers a thorough technical breakdown of Sendmail features documentation and configuration examples. http://www.sendmail.com/ — Contains news interviews and articles concerning Sendmail including an expanded view of the many options available. http://www.postfix.org/ — The Postfix project home page contains a wealth of information about Postfix. The mailing list is a particularly good place to look for information. http://www.fetchmail.info/fetchmail-FAQ.html — A thorough FAQ about Fetchmail. http://www.procmail.org/ — The home page for Procmail with links to assorted mailing lists dedicated to Procmail as well as various FAQ documents. http://www.uwasa.fi/ts/info/proctips.html — Contains dozens of tips that make using Procmail much easier. Includes instructions on how to test .procmailrc files and use Procmail scoring to decide if a particular action should be taken. http://www.spamassassin.org/ — The official site of the SpamAssassin project. 13.6.3. Related Books Sendmail Milters: A Guide for Fighting Spam by Bryan Costales and Marcia Flynt Addison-Wesley — A good Sendmail guide that can help you customize your mail filters. Sendmail by Bryan Costales with Eric Allman et al. OReilly Associates — A good Sendmail reference written with the assistance of the original creator of Delivermail and Sendmail. Removing the Spam: Email Processing and Filtering by Geoff Mulligan Addison-Wesley Publishing Company — A volume that looks at various methods used by email administrators using established tools such as Sendmail and Procmail to manage spam problems. Internet Email Protocols: A Developers Guide by Kevin Johnson Addison-Wesley Publishing Company — Provides a very thorough review of major email protocols and the security they provide. ⁠Chapt er 1 3. Mail Servers 207

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Managing IMAP by Dianna Mullet and Kevin Mullet OReilly Associates — Details the steps required to configure an IMAP server. Syst em Administ rat ors Guide 208

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Chapter 14. File and Print Servers This chapter guides you through the installation and configuration of Samba an open source implementation of the Server Message Block SMB and common Internet file system CIFS protocol and vsftpd the primary FTP server shipped with Red Hat Enterprise Linux. Additionally it explains how to use the Print Settings tool to configure printers. 14.1. Samba Samba is the standard open source Windows interoperability suite of programs for Linux. It implements the server message block SMB protocol. SMB allows Microsoft Windows® Linux UNIX and other operating systems to access files and printers shared from servers that support this protocol. Sambas use of SMB allows it to appear as a Windows server to Windows clients. Note In order to use Samba first ensure the samba package is installed on your system by running as root: yum install samba For more information on installing packages with Yum see Section 8.2.4 “Installing Packages”. 14 .1.1. Introduction to Samba Samba is an important component to seamlessly integrate Linux Servers and Desktops into Active Directory AD environments. It can function both as a domain controller NT4-style or as a regular domain member AD or NT4-style. What Samba can do : Serve directory trees and printers to Linux UNIX and Windows clients Assist in network browsing with NetBIOS Authenticate Windows domain logins Provide Windows Internet Name Service WINS name server resolution Act as a Windows NT® -style Primary Domain Controller PDC Act as a Backup Domain Controller BDC for a Samba-based PDC Act as an Active Directory domain member server Join a Windows NT/2000/2003/2008 PDC/Windows Server 2012 What Samba canno t do : Act as a BDC for a Windows PDC and vice versa ⁠Chapt er 1 4 . File and Print Servers 209

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Act as an Active Directory domain controller 14 .1.2. Samba Daemons and Related Services Samba is comprised of three daemons smbd nmbd and winbindd. Three services smb nmb and winbind control how the daemons are started stopped and other service-related features. These services act as different init scripts. Each daemon is listed in detail below as well as which specific service has control over it. smbd The smbd server daemon provides file sharing and printing services to Windows clients. In addition it is responsible for user authentication resource locking and data sharing through the SMB protocol. The default ports on which the server listens for SMB traffic are TCP ports 139 and 445. The smbd daemon is controlled by the smb service. nmbd The nmbd server daemon understands and replies to NetBIOS name service requests such as those produced by SMB/CIFS in Windows-based systems. These systems include Windows 95/98/ME Windows NT Windows 2000 Windows XP and LanManager clients. It also participates in the browsing protocols that make up the Windows Network Neighborhood view. The default port that the server listens to for NMB traffic is UDP port 137. The nmbd daemon is controlled by the nmb service. winbindd The winbind service resolves user and group information received from a server running Windows NT 2000 2003 Windows Server 2008 or Windows Server 2012. This makes Windows user and group information understandable by UNIX platforms. This is achieved by using Microsoft RPC calls Pluggable Authentication Modules PAM and the Name Service Switch NSS. This allows Windows NT domain and Active Directory users to appear and operate as UNIX users on a UNIX machine. Though bundled with the Samba distribution the winbind service is controlled separately from the smb service. The winbind daemon is controlled by the winbind service and does not require the smb service to be started in order to operate. winbind is also used when Samba is an Active Directory member and may also be used on a Samba domain controller to implement nested groups and interdomain trust. Because winbind is a client-side service used to connect to Windows NT-based servers further discussion of winbind is beyond the scope of this chapter. Note See Section 14.1.9 “Samba Distribution Programs” for a list of utilities included in the Samba distribution. 14 .1.3. Connecting to a Samba Share You can use either Nautilus or command line to connect to available Samba shares. Procedure 14 .1. Connecting to a Samba Share Using Nautilus Syst em Administ rat ors Guide 210

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1. To view a list of Samba workgroups and domains on your network select Places → Network from the GNOME panel and then select the desired network. Alternatively type smb: in the File → Open Location bar of Nautilus. As shown in Figure 14.1 “SMB Workgroups in Nautilus” an icon appears for each available SMB workgroup or domain on the network. Figure 14 .1. SMB Workgroups in Nautilus 2. Double-click one of the workgroup or domain icon to view a list of computers within the workgroup or domain. ⁠Chapt er 1 4 . File and Print Servers 211

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Figure 14 .2. SMB Machines in Nautilus 3. As displayed in Figure 14.2 “SMB Machines in Nautilus” an icon exists for each machine within the workgroup. Double-click on an icon to view the Samba shares on the machine. If a user name and password combination is required you are prompted for them. Alternately you can also specify the Samba server and sharename in the Location: bar for Nautilus using the following syntax replace servername and sharename with the appropriate values: smb://servername/sharename Procedure 14 .2. Connecting to a Samba Share Using the Command Line 1. To connect to a Samba share from a shell prompt type the following command: smbclient //hostname/sharename -U username Replace hostname with the host name or IP address of the Samba server you want to connect to sharename with the name of the shared directory you want to browse and username with the Samba user name for the system. Enter the correct password or press Enter if no password is required for the user. If you see the smb:\ prompt you have successfully logged in. Once you are logged in type help for a list of commands. If you want to browse the contents of your home directory replace sharename with your user name. If the -U switch is not used the user name of the current user is passed to the Samba server. 2. To exit smbclient type exit at the smb:\ prompt. 14 .1.4 . Mounting the Share Syst em Administ rat ors Guide 212

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Sometimes it is useful to mount a Samba share to a directory so that the files in the directory can be treated as if they are part of the local file system. To mount a Samba share to a directory create a directory to mount it to if it does not already exist and execute the following command as root: mount -t cifs //servername/sharename /mnt/point/ -o usernameusernamepasswordpassword This command mounts sharename from servername in the local directory /mnt/point/. For more information about mounting a samba share see the mount.cifs8 manual page. Note The mount.cifs utility is a separate RPM independent from Samba. In order to use mount.cifs first ensure the cifs-utils package is installed on your system by running as root: yum install cifs-utils For more information on installing packages with Yum see Section 8.2.4 “Installing Packages”. Note that the cifs-utils package also contains the cifs.upcall binary called by the kernel in order to perform kerberized CIFS mounts. For more information on cifs.upcall see the cifs.upcall8 manual page. Warning Some CIFS servers require plain text passwords for authentication. Support for plain text password authentication can be enabled using the following command as root: echo 0x37 /proc/fs/cifs/SecurityFlags WARNING: This operation can expose passwords by removing password encryption. 14 .1.5. Configuring a Samba Server The default configuration file /etc/samba/smb.conf allows users to view their home directories as a Samba share. It also shares all printers configured for the system as Samba shared printers. You can attach a printer to the system and print to it from the Windows machines on your network. 14.1.5.1. Graphical Co nfigurat io n To configure Samba using a graphical interface use one of the available Samba graphical user interfaces. A list of available GUIs can be found at http://www.samba.org/samba/GUI/. ⁠Chapt er 1 4 . File and Print Servers 213

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14.1.5.2. Co mmand-Line Co nfigurat io n Samba uses /etc/samba/smb.conf as its configuration file. If you change this configuration file the changes do not take effect until you restart the Samba daemon with the following command as root: systemctl restart smb.service To specify the Windows workgroup and a brief description of the Samba server edit the following lines in your /etc/samba/smb.conf file: workgroup WORKGROUPNAME server string BRIEF COMMENT ABOUT SERVER Replace WORKGROUPNAME with the name of the Windows workgroup to which this machine should belong. The BRIEF COMMENT ABOUT SERVER is optional and is used as the Windows comment about the Samba system. To create a Samba share directory on your Linux system add the following section to your /etc/samba/smb.conf file after modifying it to reflect your needs and your system: Example 14 .1. An Example Configuration of a Samba Server sharename comment Insert a comment here path /home/share/ valid users tfox carole writable yes create mask 0765 The above example allows the users tfox and carole to read and write to the directory /home/share/ on the Samba server from a Samba client. 14.1.5.3. Encrypt ed Passwo rds Encrypted passwords are enabled by default because it is more secure to use them. To create a user with an encrypted password use the smbpasswd utility: smbpasswd -a username 14 .1.6. Starting and Stopping Samba To start a Samba server type the following command in a shell prompt as root: systemctl start smb.service Syst em Administ rat ors Guide 214

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Important To set up a domain member server you must first join the domain or Active Directory using the net join command before starting the smb service. Also it is recommended to run winbind before smbd. To stop the server type the following command in a shell prompt as root: systemctl stop smb.service The restart option is a quick way of stopping and then starting Samba. This is the most reliable way to make configuration changes take effect after editing the configuration file for Samba. Note that the restart option starts the daemon even if it was not running originally. To restart the server type the following command in a shell prompt as root: systemctl restart smb.service The condrestart conditional restart option only starts smb on the condition that it is currently running. This option is useful for scripts because it does not start the daemon if it is not running. Note When the /etc/samba/smb.conf file is changed Samba automatically reloads it after a few minutes. Issuing a manual restart or reload is just as effective. To conditionally restart the server type the following command as root: systemctl try-restart smb.service A manual reload of the /etc/samba/smb.conf file can be useful in case of a failed automatic reload by the smb service. To ensure that the Samba server configuration file is reloaded without restarting the service type the following command as root: systemctl reload smb.service By default the smb service does not start automatically at boot time. To configure Samba to start at boot time type the following at a shell prompt as root: systemctl enable smb.service See Chapter 9 Managing Services with systemd for more information regarding this tool. 14 .1.7. Samba Security Modes There are only two types of security modes for Samba share-level and user-level which are collectively known as security levels. Share-level security is deprecated and has been removed from Samba. Configurations containing this mode need to be migrated to use user-level security. User- level security can be implemented in one of three different ways. The different ways of implementing a security level are called security modes. ⁠Chapt er 1 4 . File and Print Servers 215

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14.1.7.1. User-Level Securit y User-level security is the default and recommended setting for Samba. Even if the security user directive is not listed in the /etc/samba/smb.conf file it is used by Samba. If the server accepts the clients user name and password the client can then mount multiple shares without specifying a password for each instance. Samba can also accept session-based user name and password requests. The client maintains multiple authentication contexts by using a unique UID for each logon. In the /etc/samba/smb.conf file the security user directive that sets user-level security is: GLOBAL ... security user ... Samba Guest Shares As mentioned above share-level security mode is deprecated. To configure a Samba guest share without using the security share parameter follow the procedure below: Procedure 14 .3. Configuring Samba Guest Shares 1. Create a username map file in this example /etc/samba/smbusers and add the following line to it: nobody guest 2. Add the following directives to the main section in the /etc/samba/smb.conf file. Also do not use the valid users directive: GLOBAL ... security user map to guest Bad User username map /etc/samba/smbusers ... The username map directive provides a path to the username map file specified in the previous step. 3. Add the following directive to the share section in the /ect/samba/smb.conf file. Do not use the valid users directive. SHARE ... guest ok yes ... The following sections describe other implementations of user-level security. Do main Securit y Mo de User-Level Securit y In domain security mode the Samba server has a machine account domain security trust account and causes all authentication requests to be passed through to the domain controllers. The Samba Syst em Administ rat ors Guide 216

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server is made into a domain member server by using the following directives in the /etc/samba/smb.conf file: GLOBAL ... security domain workgroup MARKETING ... Act ive Direct o ry Securit y Mo de User-Level Securit y If you have an Active Directory environment it is possible to join the domain as a native Active Directory member. Even if a security policy restricts the use of NT-compatible authentication protocols the Samba server can join an ADS using Kerberos. Samba in Active Directory member mode can accept Kerberos tickets. In the /etc/samba/smb.conf file the following directives make Samba an Active Directory member server: GLOBAL ... security ADS realm EXAMPLE.COM password server kerberos.example.com ... 14.1.7.2. Share-Level Securit y With share-level security the server accepts only a password without an explicit user name from the client. The server expects a password for each share independent of the user name. There have been recent reports that Microsoft Windows clients have compatibility issues with share-level security servers. This mode is deprecated and has been removed from Samba. Configurations containing security share should be updated to use user-level security. Follow the steps in Procedure 14.3 “Configuring Samba Guest Shares” to avoid using the security share directive. 14 .1.8. Samba Network Browsing Network browsing enables Windows and Samba servers to appear in the Windows Network Neighborhood. Inside the Network Neighborhood icons are represented as servers and if opened the servers shares and printers that are available are displayed. Network browsing capabilities require NetBIOS over TCP/IP. NetBIOS-based networking uses broadcast UDP messaging to accomplish browse list management. Without NetBIOS and WINS as the primary method for TCP/IP host name resolution other methods such as static files /etc/hosts or DNS must be used. A domain master browser collates the browse lists from local master browsers on all subnets so that browsing can occur between workgroups and subnets. Also the domain master browser should preferably be the local master browser for its own subnet. 14.1.8.1. Do main Bro wsing By default a Windows server PDC for a domain is also the domain master browser for that domain. A Samba server must not be set up as a domain master server in this type of situation. ⁠Chapt er 1 4 . File and Print Servers 217

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For subnets that do not include the Windows server PDC a Samba server can be implemented as a local master browser. Configuring the /etc/samba/smb.conf file for a local master browser or no browsing at all in a domain controller environment is the same as workgroup configuration see Section 14.1.5 “Configuring a Samba Server”. 14.1.8.2. WINS Windo ws Int ernet Name Server Either a Samba server or a Windows NT server can function as a WINS server. When a WINS server is used with NetBIOS enabled UDP unicasts can be routed which allows name resolution across networks. Without a WINS server the UDP broadcast is limited to the local subnet and therefore cannot be routed to other subnets workgroups or domains. If WINS replication is necessary do not use Samba as your primary WINS server as Samba does not currently support WINS replication. In a mixed NT/2000/2003/2008 server and Samba environment it is recommended that you use the Microsoft WINS capabilities. In a Samba-only environment it is recommended that you use only one Samba server for WINS. The following is an example of the /etc/samba/smb.conf file in which the Samba server is serving as a WINS server: Example 14 .2. An Example Configuration of WINS Server global wins support yes Note All servers including Samba should connect to a WINS server to resolve NetBIOS names. Without WINS browsing only occurs on the local subnet. Furthermore even if a domain-wide list is somehow obtained hosts cannot be resolved for the client without WINS. 14 .1.9. Samba Distribution Programs net net protocol function misc_options target_options The net utility is similar to the net utility used for Windows and MS-DOS. The first argument is used to specify the protocol to use when executing a command. The protocol option can be ads rap or rpc for specifying the type of server connection. Active Directory uses ads Win9x/NT3 uses rap and Windows NT4/2000/2003/2008 uses rpc. If the protocol is omitted net automatically tries to determine it. The following example displays a list of the available shares for a host named wakko: net -l share -S wakko Password: Enumerating shared resources exports on remote server: Share name Type Description Syst em Administ rat ors Guide 218

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---------- ---- ----------- data Disk Wakko data share tmp Disk Wakko tmp share IPC IPC IPC Service Samba Server ADMIN IPC IPC Service Samba Server The following example displays a list of Samba users for a host named wakko: net -l user -S wakko root password: User name Comment ----------------------------- andriusb Documentation joe Marketing lisa Sales nmblookup nmblookup options netbios_name The nmblookup program resolves NetBIOS names into IP addresses. The program broadcasts its query on the local subnet until the target machine replies. The following example displays the IP address of the NetBIOS name trek: nmblookup trek querying trek on 10.1.59.255 10.1.56.45 trek00 pdbedit pdbedit options The pdbedit program manages accounts located in the SAM database. All back ends are supported including smbpasswd LDAP and the tdb database library. The following are examples of adding deleting and listing users: pdbedit -a kristin new password: retype new password: Unix username: kristin NT username: Account Flags: U User SID: S-1-5-21-1210235352-3804200048-1474496110-2012 Primary Group SID: S-1-5-21-1210235352-3804200048-1474496110-2077 Full Name: Home Directory: \\wakko\kristin HomeDir Drive: Logon Script: Profile Path: \\wakko\kristin\profile Domain: WAKKO Account desc: Workstations: Munged ⁠Chapt er 1 4 . File and Print Servers 219

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dial: Logon time: 0 Logoff time: Mon 18 Jan 2038 22:14:07 GMT Kickoff time: Mon 18 Jan 2038 22:14:07 GMT Password last set: Thu 29 Jan 2004 08:29:28 GMT Password can change: Thu 29 Jan 2004 08:29:28 GMT Password must change: Mon 18 Jan 2038 22:14:07 GMT pdbedit -v -L kristin Unix username: kristin NT username: Account Flags: U User SID: S-1-5-21-1210235352-3804200048-1474496110-2012 Primary Group SID: S-1-5-21-1210235352-3804200048-1474496110-2077 Full Name: Home Directory: \\wakko\kristin HomeDir Drive: Logon Script: Profile Path: \\wakko\kristin\profile Domain: WAKKO Account desc: Workstations: Munged dial: Logon time: 0 Logoff time: Mon 18 Jan 2038 22:14:07 GMT Kickoff time: Mon 18 Jan 2038 22:14:07 GMT Password last set: Thu 29 Jan 2004 08:29:28 GMT Password can change: Thu 29 Jan 2004 08:29:28 GMT Password must change: Mon 18 Jan 2038 22:14:07 GMT pdbedit -L andriusb:505: joe:503: lisa:504: kristin:506: pdbedit -x joe pdbedit -L andriusb:505: lisa:504: kristin:506: rpcclient rpcclient server options The rpcclient program issues administrative commands using Microsoft RPCs which provide access to the Windows administration graphical user interfaces GUIs for systems management. This is most often used by advanced users that understand the full complexity of Microsoft RPCs. smbcacls smbcacls //server/share filename options The smbcacls program modifies Windows ACLs on files and directories shared by a Samba server or a Windows server. smbclient Syst em Administ rat ors Guide 220

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smbclient //server/share password options The smbclient program is a versatile UNIX client which provides functionality similar to the ftp utility. smbcontrol smbcontrol -i options smbcontrol options destination messagetype parameters The smbcontrol program sends control messages to running smbd nmbd or winbindd daemons. Executing smbcontrol -i runs commands interactively until a blank line or a q is entered. smbpasswd smbpasswd options username password The smbpasswd program manages encrypted passwords. This program can be run by a superuser to change any users password and also by an ordinary user to change their own Samba password. smbspool smbspool job user title copies options filename The smbspool program is a CUPS-compatible printing interface to Samba. Although designed for use with CUPS printers smbspool can work with non-CUPS printers as well. smbstatus smbstatus options The smbstatus program displays the status of current connections to a Samba server. smbtar smbtar options The smbtar program performs backup and restores of Windows-based share files and directories to a local tape archive. Though similar to the tar utility the two are not compatible. testparm testparm options filename hostname IP_address The testparm program checks the syntax of the /etc/samba/smb.conf file. If your smb.conf file is in the default location /etc/samba/smb.conf you do not need to specify the location. Specifying the host name and IP address to the testparm program verifies that the hosts.allow and host.deny files are configured correctly. The testparm program also displays a summary of ⁠Chapt er 1 4 . File and Print Servers 221

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your smb.conf file and the servers role stand-alone domain etc. after testing. This is convenient when debugging as it excludes comments and concisely presents information for experienced administrators to read. For example: testparm Load smb config files from /etc/samba/smb.conf Processing section "homes" Processing section "printers" Processing section "tmp" Processing section "html" Loaded services file OK. Server role: ROLE_STANDALONE Press enter to see a dump of your service definitions enter Global parameters global workgroup MYGROUP server string Samba Server security SHARE log file /var/log/samba/m.log max log size 50 socket options TCP_NODELAY SO_RCVBUF8192 SO_SNDBUF8192 dns proxy no homes comment Home Directories read only no browseable no printers comment All Printers path /var/spool/samba printable yes browseable no tmp comment Wakko tmp path /tmp guest only yes html comment Wakko www path /var/www/html force user andriusb force group users read only no guest only yes wbinfo wbinfo options The wbinfo program displays information from the winbindd daemon. The winbindd daemon must be running for wbinfo to work. 14 .1.10. Additional Resources The following sections give you the means to explore Samba in greater detail. Syst em Administ rat ors Guide 222

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Inst alled Do cument at io n /usr/share/doc/samba-version-number/ — All additional files included with the Samba distribution. This includes all helper scripts sample configuration files and documentation. See the following man pages for detailed information specific Samba features: smb.conf5 samba7 smbd8 nmbd8 winbindd8 Useful Websit es http://www.samba.org/ — Homepage for the Samba distribution and all official documentation created by the Samba development team. Many resources are available in HTML and PDF formats while others are only available for purchase. Although many of these links are not Red Hat Enterprise Linux specific some concepts may apply. https://wiki.samba.org/index.php/User_Documentation — Samba 4.x official documentation. http://samba.org/samba/archives.html — Active email lists for the Samba community. Enabling digest mode is recommended due to high levels of list activity. Samba newsgroups — Samba threaded newsgroups such as www.gmane.org that use the NNTP protocol are also available. This an alternative to receiving mailing list emails. 14.2. FTP The File Transfer Protocol FTP is one of the oldest and most commonly used protocols found on the Internet today. Its purpose is to reliably transfer files between computer hosts on a network without requiring the user to log directly in to the remote host or to have knowledge of how to use the remote system. It allows users to access files on remote systems using a standard set of simple commands. This section outlines the basics of the FTP protocol and introduces vsftpd which is the preferred FTP server in Red Hat Enterprise Linux. 14 .2.1. T he File T ransfer Protocol FTP uses a client-server architecture to transfer files using the TCP network protocol. Because FTP is a rather old protocol it uses unencrypted user name and password authentication. For this reason it is considered an insecure protocol and should not be used unless absolutely necessary. However because FTP is so prevalent on the Internet it is often required for sharing files to the public. System administrators therefore should be aware of FTPs unique characteristics. This section describes how to configure vsftpd to establish connections secured by TLS and how to secure an FTP server with the help of SELinux. A good substitute for FTP is sftp from the OpenSSH suite of tools. For information about configuring OpenSSH and about the SSH protocol in general refer to Chapter 10 OpenSSH. Unlike most protocols used on the Internet FTP requires multiple network ports to work properly. When an FTP client application initiates a connection to an FTP server it opens port 21 on the ⁠Chapt er 1 4 . File and Print Servers 223

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server — known as the command port. This port is used to issue all commands to the server. Any data requested from the server is returned to the client via a data port. The port number for data connections and the way in which data connections are initialized vary depending upon whether the client requests the data in active or passive mode. The following defines these modes: active mode Active mode is the original method used by the FTP protocol for transferring data to the client application. When an active-mode data transfer is initiated by the FTP client the server opens a connection from port 20 on the server to the IP address and a random unprivileged port greater than 1024 specified by the client. This arrangement means that the client machine must be allowed to accept connections over any port above 1024. With the growth of insecure networks such as the Internet the use of firewalls for protecting client machines is now prevalent. Because these client-side firewalls often deny incoming connections from active-mode FTP servers passive mode was devised. passive mode Passive mode like active mode is initiated by the FTP client application. When requesting data from the server the FTP client indicates it wants to access the data in passive mode and the server provides the IP address and a random unprivileged port greater than 1024 on the server. The client then connects to that port on the server to download the requested information. While passive mode does resolve issues for client-side firewall interference with data connections it can complicate administration of the server-side firewall. You can reduce the number of open ports on a server by limiting the range of unprivileged ports on the FTP server. This also simplifies the process of configuring firewall rules for the server. 14 .2.2. T he vsftpd Server The Very Secure FTP Daemon vsftpd is designed from the ground up to be fast stable and most importantly secure. vsftpd is the only stand-alone FTP server distributed with Red Hat Enterprise Linux due to its ability to handle large numbers of connections efficiently and securely. The security model used by vsftpd has three primary aspects: Strong separation of privileged and non-privileged processes — Separate processes handle different tasks and each of these processes runs with the minimal privileges required for the task. Tasks requiring elevated privileges are handled by processes with the minimal privilege necessary — By taking advantage of compatibilities found in the libcap library tasks that usually require full root privileges can be executed more safely from a less privileged process. Most processes run in a chroot jail — Whenever possible processes are change-rooted to the directory being shared this directory is then considered a chroot jail. For example if the /var/ftp/ directory is the primary shared directory vsftpd reassigns /var/ftp/ to the new root directory known as /. This disallows any potential malicious hacker activities for any directories not contained in the new root directory. Use of these security practices has the following effect on how vsftpd deals with requests: The parent process runs with the least privileges required — The parent process dynamically calculates the level of privileges it requires to minimize the level of risk. Child processes handle direct interaction with the FTP clients and run with as close to no privileges as possible. Syst em Administ rat ors Guide 224

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All operations requiring elevated privileges are handled by a small parent process — Much like the Apache HTTP Server vsftpd launches unprivileged child processes to handle incoming connections. This allows the privileged parent process to be as small as possible and handle relatively few tasks. All requests from unprivileged child processes are distrusted by the parent process — Communication with child processes is received over a socket and the validity of any information from child processes is checked before being acted on. Most interactions with FTP clients are handled by unprivileged child processes in a chroot jail — Because these child processes are unprivileged and only have access to the directory being shared any crashed processes only allow the attacker access to the shared files. 14.2.2.1. St art ing and St o pping vsft pd To start the vsftpd service in the current session type the following at a shell prompt as root: systemctl start vsftpd.service To stop the service in the current session type as root: systemctl stop vsftpd.service To restart the vsftpd service run the following command as root: systemctl restart vsftpd.service This command stops and immediately starts the vsftpd service which is the most efficient way to make configuration changes take effect after editing the configuration file for this FTP server. Alternatively you can use the following command to restart the vsftpd service only if it is already running: systemctl try-restart vsftpd.service By default the vsftpd service does not start automatically at boot time. To configure the vsftpd service to start at boot time type the following at a shell prompt as root: systemctl enable vsftpd.service Created symlink from /etc/systemd/system/multi- user.target.wants/vsftpd.service to /usr/lib/systemd/system/vsftpd.service. For more information on how to manage system services in Red Hat Enterprise Linux 7 see Chapter 9 Managing Services with systemd. 14.2.2.2. St art ing Mult iple Co pies o f vsft pd Sometimes one computer is used to serve multiple FTP domains. This is a technique called multihoming. One way to multihome using vsftpd is by running multiple copies of the daemon each with its own configuration file. ⁠Chapt er 1 4 . File and Print Servers 225

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To do this first assign all relevant IP addresses to network devices or alias network devices on the system. For more information about configuring network devices device aliases and additional information about network configuration scripts see the Red Hat Enterprise Linux 7 Networking Guide. Next the DNS server for the FTP domains must be configured to reference the correct machine. For information about BIND the DNS protocol implementation used in Red Hat Enterprise Linux and its configuration files see the Red Hat Enterprise Linux 7 Networking Guide. For vsftpd to answer requests on different IP addresses multiple copies of the daemon must be running. To facilitate launching multiple instances of the vsftpd daemon a special systemd service unit vsftpd.service for launching vsftpd as an instantiated service is supplied in the vsftpd package. In order to make use of this service unit a separate vsftpd configuration file for each required instance of the FTP server must be created and placed in the /etc/vsftpd/ directory. Note that each of these configuration files must have a unique name such as /etc/vsftpd/vsftpd-site- 2.conf and must be readable and writable only by the root user. Within each configuration file for each FTP server listening on an IPv4 network the following directive must be unique: listen_addressN.N.N.N Replace N.N.N.N with a unique IP address for the FTP site being served. If the site is using IPv6 use the listen_address6 directive instead. Once there are multiple configuration files present in the /etc/vsftpd/ directory individual instances of the vsftpd daemon can be started by executing the following command as root: systemctl start vsftpdconfiguration-file-name.service In the above command replace configuration-file-name with the unique name of the requested servers configuration file such as vsftpd-site-2. Note that the configuration files .conf extension should not be included in the command. If you want to start several instances of the vsftpd daemon at once you can make use of a systemd target unit file vsftpd.target which is supplied in the vsftpd package. This systemd target causes an independent vsftpd daemon to be launched for each available vsftpd configuration file in the /etc/vsftpd/ directory. Execute the following command as root to enable the target: systemctl enable vsftpd.target Created symlink from /etc/systemd/system/multi- user.target.wants/vsftpd.target to /usr/lib/systemd/system/vsftpd.target. The above command configures the systemd service manager to launch the vsftpd service along with the configured vsftpd server instances at boot time. To start the service immediately without rebooting the system execute the following command as root: systemctl start vsftpd.target See Section 9.3 “Working with systemd Targets” for more information on how to use systemd targets to manage services. Other directives to consider altering on a per-server basis are: Syst em Administ rat ors Guide 226

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anon_root local_root vsftpd_log_file xferlog_file 14.2.2.3. Encrypt ing vsft pd Co nnect io ns Using T LS In order to counter the inherently insecure nature of FTP which transmits user names passwords and data without encryption by default the vsftpd daemon can be configured to utilize the TLS protocol to authenticate connections and encrypt all transfers. Note that an FTP client that supports TLS is needed to communicate with vsftpd with TLS enabled. Note SSL Secure Sockets Layer is the name of an older implementation of the security protocol. The new versions are called TLS Transport Layer Security. Only the newer versions TLS should be used as SSL suffers from serious security vulnerabilities. The documentation included with the vsftpd server as well as the configuration directives used in the vsftpd.conf file use the SSL name when referring to security-related matters but TLS is supported and used by default when the ssl_enable directive is set to YES. Set the ssl_enable configuration directive in the vsftpd.conf file to YES to turn on TLS support. The default settings of other TLS-related directives that become automatically active when the ssl_enable option is enabled provide for a reasonably well-configured TLS set up. This includes among other things the requirement to only use the TLS v1 protocol for all connections the use of the insecure SSL protocol versions is disabled by default or forcing all non-anonymous logins to use TLS for sending passwords and data transfers. Example 14 .3. Configuring vsftpd to Use TLS In this example the configuration directives explicitly disable the older SSL versions of the security protocol in the vsftpd.conf file: ssl_enableYES ssl_tlsv1YES ssl_sslv2NO ssl_sslv3NO Restart the vsftpd service after you modify its configuration: systemctl restart vsftpd.service See the vsftpd.conf5 manual page for other TLS-related configuration directives for fine-tuning the use of TLS by vsftpd. 14.2.2.4. SELinux Po licy fo r vsft pd ⁠Chapt er 1 4 . File and Print Servers 227

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The SELinux policy governing the vsftpd daemon as well as other ftpd processes defines a mandatory access control which by default is based on least access required. In order to allow the FTP daemon to access specific files or directories appropriate labels need to be assigned to them. For example in order to be able to share files anonymously the public_content_t label must be assigned to the files and directories to be shared. You can do this using the chcon command as root: chcon -R -t public_content_t /path/to/directory In the above command replace /path/to/directory with the path to the directory to which you want to assign the label. Similarly if you want to set up a directory for uploading files you need to assign that particular directory the public_content_rw_t label. In addition to that the allow_ftpd_anon_write SELinux Boolean option must be set to 1. Use the setsebool command as root to do that: setsebool -P allow_ftpd_anon_write1 If you want local users to be able to access their home directories through FTP which is the default setting on Red Hat Enterprise Linux 7 the ftp_home_dir Boolean option needs to be set to 1. If vsftpd is to be allowed to run in standalone mode which is also enabled by default on Red Hat Enterprise Linux 7 the ftpd_is_daemon option needs to be set to 1 as well. See the ftpd_selinux8 manual page for more information including examples of other useful labels and Boolean options on how to configure the SELinux policy pertaining to FTP. Also see the Red Hat Enterprise Linux 7 SELinux Users and Administrators Guide for more detailed information about SELinux in general. 14 .2.3. Additional Resources For more information about vsftpd see the following resources. 14.2.3.1. Inst alled Do cument at io n The /usr/share/doc/vsftpd-version-number/ directory — Replace version-number with the installed version of the vsftpd package. This directory contains a README file with basic information about the software. The TUNING file contains basic performance-tuning tips and the SECURITY/ directory contains information about the security model employed by vsftpd. vsftpd-related manual pages — There are a number of manual pages for the daemon and the configuration files. The following lists some of the more important manual pages. Server Applications vsftpd8 — Describes available command-line options for vsftpd. Configuration Files vsftpd.conf5 — Contains a detailed list of options available within the configuration file for vsftpd. hosts_access5 — Describes the format and options available within the TCP wrappers configuration files: hosts.allow and hosts.deny. Interaction with SELinux Syst em Administ rat ors Guide 228

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ftpd_selinux8 — Contains a description of the SELinux policy governing ftpd processes as well as an explanation of the way SELinux labels need to be assigned and Booleans set. 14.2.3.2. Online Do cument at io n About vsftpd and FTP in General http://vsftpd.beasts.org/ — The vsftpd project page is a great place to locate the latest documentation and to contact the author of the software. http://slacksite.com/other/ftp.html — This website provides a concise explanation of the differences between active and passive-mode FTP. Red Hat Enterprise Linux Documentation Red Hat Enterprise Linux 7 Networking Guide — The Networking Guide for Red Hat Enterprise Linux 7 documents relevant information regarding the configuration and administration of network interfaces networks and network services in this system. It provides an introduction to the hostnamectl utility and explains how to use it to view and set host names on the command line both locally and remotely. Red Hat Enterprise Linux 7 SELinux Users and Administrators Guide — The SELinux Users and Administrators Guide for Red Hat Enterprise Linux 7 describes the basic principles of SELinux and documents in detail how to configure and use SELinux with various services such as the Apache HTTP Server Postfix PostgreSQL or OpenShift. It explains how to configure SELinux access permissions for system services managed by systemd. Red Hat Enterprise Linux 7 Security Guide — The Security Guide for Red Hat Enterprise Linux 7 assists users and administrators in learning the processes and practices of securing their workstations and servers against local and remote intrusion exploitation and malicious activity. It also explains how to secure critical system services. Relevant RFC Documents RFC 0959 — The original Request for Comments RFC of the FTP protocol from the IETF. RFC 1123 — The small FTP-related section extends and clarifies RFC 0959. RFC 2228 — FTP security extensions. vsftpd implements the small subset needed to support TLS and SSL connections. RFC 2389 — Proposes FEAT and OPTS commands. RFC 2428 — IPv6 support. 14.3. Print Settings The Print Settings tool serves for printer configuring maintenance of printer configuration files print spool directories and print filters and printer classes management. The tool is based on the Common Unix Printing System CUPS. If you upgraded the system from a previous Red Hat Enterprise Linux version that used CUPS the upgrade process preserved the configured printers. ⁠Chapt er 1 4 . File and Print Servers 229

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Important The cupsd.conf man page documents configuration of a CUPS server. It includes directives for enabling SSL support. However CUPS does not allow control of the protocol versions used. Due to the vulnerability described in Resolution for POODLE SSLv3.0 vulnerability CVE- 2014-3566 for components that do not allow SSLv3 to be disabled via configuration settings Red Hat recommends that you do not rely on this for security. It is recommend that you use stunnel to provide a secure tunnel and disable SSLv3. For more information on using stunnel see the Red Hat Enterprise Linux 7 Security Guide. For ad-hoc secure connections to a remote systems Print Settings tool use X11 forwarding over SSH as described in Section 10.4.1 “X11 Forwarding”. Note You can perform the same and additional operations on printers directly from the CUPS web application or command line. To access the application in a web browser go to http://localhost:631/. For CUPS manuals refer to the links on the Home tab of the web site. 14 .3.1. Starting the Print Settings Configuration T ool With the Print Settings configuration tool you can perform various operations on existing printers and set up new printers. You can also use CUPS directly go to http://localhost:631/ to access the CUPS web application. To start the Print Settings tool from the command line type system-config-printer at a shell prompt. The Print Settings tool appears. Alternatively if using the GNOME desktop press the Super key to enter the Activities Overview type Print Settings and then press Enter. The Print Settings tool appears. The Super key appears in a variety of guises depending on the keyboard and other hardware but often as either the Windows or Command key and typically to the left of the Spacebar. The Print Settings window depicted in Figure 14.3 “Print Settings window” appears. Syst em Administ rat ors Guide 230

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Figure 14 .3. Print Settings window 14 .3.2. Starting Printer Setup Printer setup process varies depending on the printer queue type. If you are setting up a local printer connected with USB the printer is discovered and added automatically. You will be prompted to confirm the packages to be installed and provide an administrator or the root user password. Local printers connected with other port types and network printers need to be set up manually. Follow this procedure to start a manual printer setup: 1. Start the Print Settings tool refer to Section 14.3.1 “Starting the Print Settings Configuration Tool”. 2. Go to Server → New → Printer. 3. In the Authenticate dialog box enter an administrator or root user password. If this is the first time you have configured a remote printer you will be prompted to authorize an adjustment to the firewall. 4. Select the printer connection type and provide its details in the area on the right. 14 .3.3. Adding a Local Printer Follow this procedure to add a local printer connected with other than a serial port: 1. Open the Add printer dialog refer to Section 14.3.2 “Starting Printer Setup”. 2. If the device does not appear automatically select the port to which the printer is connected in the list on the left such as Serial Port 1 or LPT 1. 3. On the right enter the connection properties: for Other ⁠Chapt er 1 4 . File and Print Servers 231

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URI for example file:/dev/lp0 for Serial Port Baud Rate Parity Data Bits Flow Control Figure 14 .4 . Adding a local printer 4. Click Forward. 5. Select the printer model. See Section 14.3.8 “Selecting the Printer Model and Finishing” for details. 14 .3.4 . Adding an AppSocket/HP JetDirect printer Follow this procedure to add an AppSocket/HP JetDirect printer: 1. Open the New Printer dialog refer to Section 14.3.1 “Starting the Print Settings Configuration Tool”. Syst em Administ rat ors Guide 232

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2. In the list on the left select Network Printer → AppSocket/HP JetDirect. 3. On the right enter the connection settings: Hostname Printer host name or IP address. Port Number Printer port listening for print jobs 9100 by default. Figure 14 .5. Adding a JetDirect printer 4. Click Forward. 5. Select the printer model. See Section 14.3.8 “Selecting the Printer Model and Finishing” for details. 14 .3.5. Adding an IPP Printer An IPP printer is a printer attached to a different system on the same TCP/IP network. The system this printer is attached to may either be running CUPS or simply configured to use IPP. ⁠Chapt er 1 4 . File and Print Servers 233

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If a firewall is enabled on the printer server then the firewall must be configured to allow incoming TCP connections on port 631. Note that the CUPS browsing protocol allows client machines to discover shared CUPS queues automatically. To enable this the firewall on the client machine must be configured to allow incoming UDP packets on port 631. Follow this procedure to add an IPP printer: 1. Open the New Printer dialog refer to Section 14.3.2 “Starting Printer Setup”. 2. In the list of devices on the left select Network Printer and Internet Printing Protocol ipp or Internet Printing Protocol https. 3. On the right enter the connection settings: Host The host name of the IPP printer. Queue The queue name to be given to the new queue if the box is left empty a name based on the device node will be used. Figure 14 .6 . Adding an IPP printer 4. Click Forward to continue. 5. Select the printer model. See Section 14.3.8 “Selecting the Printer Model and Finishing” for details. Syst em Administ rat ors Guide 234

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14 .3.6. Adding an LPD/LPR Host or Printer Follow this procedure to add an LPD/LPR host or printer: 1. Open the New Printer dialog refer to Section 14.3.2 “Starting Printer Setup”. 2. In the list of devices on the left select Network Printer → LPD/LPR Host or Printer. 3. On the right enter the connection settings: Host The host name of the LPD/LPR printer or host. Optionally click Probe to find queues on the LPD host. Queue The queue name to be given to the new queue if the box is left empty a name based on the device node will be used. Figure 14 .7. Adding an LPD/LPR printer 4. Click Forward to continue. 5. Select the printer model. See Section 14.3.8 “Selecting the Printer Model and Finishing” for details. 14 .3.7. Adding a Samba SMB printer ⁠Chapt er 1 4 . File and Print Servers 235

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14 .3.7. Adding a Samba SMB printer Follow this procedure to add a Samba printer: Note Note that in order to add a Samba printer you need to have the samba-client package installed. You can do so by running as root: yum install samba-client For more information on installing packages with Yum refer to Section 8.2.4 “Installing Packages”. 1. Open the New Printer dialog refer to Section 14.3.2 “Starting Printer Setup”. 2. In the list on the left select Network Printer → Windows Printer via SAMBA. 3. Enter the SMB address in the smb:// field. Use the format computer name/printer share. In Figure 14.8 “Adding a SMB printer” the computer name is dellbox and the printer share is r2. Figure 14 .8. Adding a SMB printer Syst em Administ rat ors Guide 236

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4. Click Browse to see the available workgroups/domains. To display only queues of a particular host type in the host name NetBios name and click Browse. 5. Select either of the options: A. Prompt user if authentication is required: user name and password are collected from the user when printing a document. B. Set authentication details now: provide authentication information now so it is not required later. In the Username field enter the user name to access the printer. This user must exist on the SMB system and the user must have permission to access the printer. The default user name is typically guest for Windows servers or nobody for Samba servers. 6. Enter the Password if required for the user specified in the Username field. Warning Samba printer user names and passwords are stored in the printer server as unencrypted files readable by root and the Linux Printing Daemon lpd. Thus other users that have root access to the printer server can view the user name and password you use to access the Samba printer. Therefore when you choose a user name and password to access a Samba printer it is advisable that you choose a password that is different from what you use to access your local Red Hat Enterprise Linux system. If there are files shared on the Samba print server it is recommended that they also use a password different from what is used by the print queue. 7. Click Verify to test the connection. Upon successful verification a dialog box appears confirming printer share accessibility. 8. Click Forward. 9. Select the printer model. See Section 14.3.8 “Selecting the Printer Model and Finishing” for details. 14 .3.8. Selecting the Printer Model and Finishing Once you have properly selected a printer connection type the system attempts to acquire a driver. If the process fails you can locate or search for the driver resources manually. Follow this procedure to provide the printer driver and finish the installation: 1. In the window displayed after the automatic driver detection has failed select one of the following options: A. Select a Printer from database — the system chooses a driver based on the selected make of your printer from the list of Makes. If your printer model is not listed choose Generic. B. Provide PPD file — the system uses the provided PostScript Printer Description PPD file for installation. A PPD file may also be delivered with your printer as being normally provided by the manufacturer. If the PPD file is available you can choose this option and use the browser bar below the option description to select the PPD file. ⁠Chapt er 1 4 . File and Print Servers 237

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C. Search for a printer driver to download — enter the make and model of your printer into the Make and model field to search on OpenPrinting.org for the appropriate packages. Figure 14 .9 . Selecting a printer brand 2. Depending on your previous choice provide details in the area displayed below: Printer brand for the Select printer from database option. PPD file location for the Provide PPD file option. Printer make and model for the Search for a printer driver to download option. 3. Click Forward to continue. 4. If applicable for your option window shown in Figure 14.10 “Selecting a printer model” appears. Choose the corresponding model in the Models column on the left. Syst em Administ rat ors Guide 238

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Note On the right the recommended printer driver is automatically selected however you can select another available driver. The print driver processes the data that you want to print into a format the printer can understand. Since a local printer is attached directly to your computer you need a printer driver to process the data that is sent to the printer. Figure 14 .10. Selecting a printer model 5. Click Forward. 6. Under the Describe Printer enter a unique name for the printer in the Printer Name field. The printer name can contain letters numbers dashes - and underscores _ it must not contain any spaces. You can also use the Description and Location fields to add further printer information. Both fields are optional and may contain spaces. ⁠Chapt er 1 4 . File and Print Servers 239

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Figure 14 .11. Printer setup 7. Click Apply to confirm your printer configuration and add the print queue if the settings are correct. Click Back to modify the printer configuration. 8. After the changes are applied a dialog box appears allowing you to print a test page. Click Yes to print a test page now. Alternatively you can print a test page later as described in Section 14.3.9 “Printing a Test Page”. 14 .3.9. Printing a T est Page After you have set up a printer or changed a printer configuration print a test page to make sure the printer is functioning properly: 1. Right-click the printer in the Printing window and click Properties. 2. In the Properties window click Settings on the left. 3. On the displayed Settings tab click the Print Test Page button. 14 .3.10. Modifying Existing Printers To delete an existing printer in the Print Settings window select the printer and go to Printer → Delete. Confirm the printer deletion. Alternatively press the Delete key. To set the default printer right-click the printer in the printer list and click the Set as Default button in the context menu. Syst em Administ rat ors Guide 24 0

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14.3.10.1. T he Set t ings Page To change printer driver configuration double-click the corresponding name in the Printer list and click the Settings label on the left to display the Settings page. You can modify printer settings such as make and model print a test page change the device location URI and more. Figure 14 .12. Settings page 14.3.10.2. T he Po licies Page Click the Policies button on the left to change settings in printer state and print output. You can select the printer states configure the Error Policy of the printer you can decide to abort the print job retry or stop it if an error occurs. You can also create a banner page a page that describes aspects of the print job such as the originating printer the user name from the which the job originated and the security status of the document being printed: click the Starting Banner or Ending Banner drop-down menu and choose the option that best describes the nature of the print jobs for example confidential. 14 .3.10.2.1. Sharing Printers On the Policies page you can mark a printer as shared: if a printer is shared users published on the network can use it. To allow the sharing function for printers go to Server → Settings and select Publish shared printers connected to this system. ⁠Chapt er 1 4 . File and Print Servers 24 1

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Figure 14 .13. Policies page Make sure that the firewall allows incoming TCP connections to port 631 the port for the Network Printing Server IPP protocol. To allow IPP traffic through the firewall on Red Hat Enterprise Linux 7 make use of firewallds IPP service. To do so proceed as follows: Procedure 14 .4 . Enabling IPP Service in firewalld 1. To start the graphical firewall-config tool press the Super key to enter the Activities Overview type firewall and then press Enter. The Firewall Configuration window opens. You will be prompted for an administrator or root password. Alternatively to start the graphical firewall configuration tool using the command line enter the following command as root user: firewall-config The Firewall Configuration window opens. Look for the word “Connected” in the lower left corner. This indicates that the firewall- config tool is connected to the user space daemon firewalld. To immediately change the current firewall settings ensure the drop-down selection menu labeled Configuration is set to Runtime. Alternatively to edit the settings to be applied at the next system start or firewall reload select Permanent from the drop-down list. 2. Select the Zones tab and then select the firewall zone to correspond with the network interface to be used. The default is the public zone. The Interfaces tab shows what interfaces have been assigned to a zone. 3. Select the Services tab and then select the ipp service to enable sharing. The ipp-client service is required for accessing network printers. Syst em Administ rat ors Guide 24 2

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4. Close the firewall-config tool. For more information on opening and closing ports in firewalld see the Red Hat Enterprise Linux 7 Security Guide. 14 .3.10.2.2. The Access Control Page You can change user-level access to the configured printer on the Access Control page. Click the Access Control label on the left to display the page. Select either Allow printing for everyone except these users or Deny printing for everyone except these users and define the user set below: enter the user name in the text box and click the Add button to add the user to the user set. Figure 14 .14 . Access Control page 14 .3.10.2.3. The Printer Options Page The Printer Options page contains various configuration options for the printer media and output and its content may vary from printer to printer. It contains general printing paper quality and printing size settings. ⁠Chapt er 1 4 . File and Print Servers 24 3

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Figure 14 .15. Printer Options page 14 .3.10.2.4 . Job Options Page On the Job Options page you can detail the printer job options. Click the Job Options label on the left to display the page. Edit the default settings to apply custom job options such as number of copies orientation pages per side scaling increase or decrease the size of the printable area which can be used to fit an oversize print area onto a smaller physical sheet of print medium detailed text options and custom job options. Syst em Administ rat ors Guide 24 4

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Figure 14 .16 . Job Options page 14 .3.10.2.5. Ink/Toner Levels Page The Ink/Toner Levels page contains details on toner status if available and printer status messages. Click the Ink/Toner Levels label on the left to display the page. ⁠Chapt er 1 4 . File and Print Servers 24 5

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Figure 14 .17. Ink/Toner Levels page 14.3.10.3. Managing Print Jo bs When you send a print job to the printer daemon such as printing a text file from Emacs or printing an image from GIMP the print job is added to the print spool queue. The print spool queue is a list of print jobs that have been sent to the printer and information about each print request such as the status of the request the job number and more. During the printing process the Printer Status icon appears in the Notification Area on the panel. To check the status of a print job click the Printer Status which displays a window similar to Figure 14.18 “GNOME Print Status”. Figure 14 .18. GNOME Print Status To cancel hold release reprint or authenticate a print job select the job in the GNOME Print Status and on the Job menu click the respective command. Syst em Administ rat ors Guide 24 6

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To view the list of print jobs in the print spool from a shell prompt type the command lpstat -o. The last few lines look similar to the following: Example 14 .4 . Example of lpstat -o output lpstat -o Charlie-60 twaugh 1024 Tue 08 Feb 2011 16:42:11 GMT Aaron-61 twaugh 1024 Tue 08 Feb 2011 16:42:44 GMT Ben-62 root 1024 Tue 08 Feb 2011 16:45:42 GMT If you want to cancel a print job find the job number of the request with the command lpstat -o and then use the command cancel job number. For example cancel 60 would cancel the print job in Example 14.4 “Example of lpstat -o output”. You cannot cancel print jobs that were started by other users with the cancel command. However you can enforce deletion of such job by issuing the cancel -U root job_number command. To prevent such canceling change the printer operation policy to Authenticated to force root authentication. You can also print a file directly from a shell prompt. For example the command lp sample.txt prints the text file sample.txt. The print filter determines what type of file it is and converts it into a format the printer can understand. 14 .3.11. Additional Resources To learn more about printing on Red Hat Enterprise Linux see the following resources. Installed Documentation lp1 — The manual page for the lp command that allows you to print files from the command line. lpr1 — The manual page for the lpr command that allows you to print files from the command line. cancel1 — The manual page for the command-line utility to remove print jobs from the print queue. mpage1 — The manual page for the command-line utility to print multiple pages on one sheet of paper. cupsd8 — The manual page for the CUPS printer daemon. cupsd.conf5 — The manual page for the CUPS printer daemon configuration file. classes.conf5 — The manual page for the class configuration file for CUPS. lpstat1 — The manual page for the lpstat command which displays status information about classes jobs and printers. Online Documentation ⁠Chapt er 1 4 . File and Print Servers 24 7

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http://www.linuxprinting.org/ — The OpenPrinting group on the Linux Foundation website contains a large amount of information about printing in Linux. http://www.cups.org/ — The CUPS website provides documentation FAQs and newsgroups about CUPS. Syst em Administ rat ors Guide 24 8

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Chapter 15. Configuring NTP Using the chrony Suite Accurate time keeping is important for a number of reasons in IT. In networking for example accurate time stamps in packets and logs are required. In Linux systems the NTP protocol is implemented by a daemon running in user space. The user space daemon updates the system clock running in the kernel. The system clock can keep time by using various clock sources. Usually the Time Stamp Counter TSC is used. The TSC is a CPU register which counts the number of cycles since it was last reset. It is very fast has a high resolution and there are no interrupts. There is a choice between the daemons ntpd and chronyd which are available from the repositories in the ntp and chrony packages respectively. This section describes the use of the chrony suite of utilities to update the system clock on systems that do not fit into the conventional permanently networked always on dedicated server category. 15.1. Introduction to the chrony Suite Chrony consists of chronyd a daemon that runs in user space and chronyc a command line program for making adjustments to chronyd. Systems which are not permanently connected or not permanently powered up take a relatively long time to adjust their system clocks with ntpd. This is because many small corrections are made based on observations of the clocks drift and offset. Temperature changes which may be significant when powering up a system affect the stability of hardware clocks. Although adjustments begin within a few milliseconds of booting a system acceptable accuracy may take anything from ten seconds from a warm restart to a number of hours depending on your requirements operating environment and hardware. chrony is a different implementation of the NTP protocol than ntpd it can adjust the system clock more rapidly. 15.1.1. Differences Between ntpd and chronyd One of the main differences between ntpd and chronyd is in the algorithms used to control the computers clock. Things chronyd can do better than ntpd are: chronyd can work well when external time references are only intermittently accessible whereas ntpd needs regular polling of time reference to work well. chronyd can perform well even when the network is congested for longer periods of time. chronyd can usually synchronize the clock faster and with better time accuracy. chronyd quickly adapts to sudden changes in the rate of the clock for example due to changes in the temperature of the crystal oscillator whereas ntpd may need a long time to settle down again. In the default configuration chronyd never steps the time after the clock has been synchronized at system start in order not to upset other running programs. ntpd can be configured to never step the time too but it has to use a different means of adjusting the clock which has some disadvantages. chronyd can adjust the rate of the clock on a Linux system in a larger range which allows it to operate even on machines with a broken or unstable clock. For example on some virtual machines. Things chronyd can do that ntpd cannot do: ⁠Chapt er 1 5. Configuring NT P Using t he chrony Suit e 24 9

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chronyd provides support for isolated networks where the only method of time correction is manual entry. For example by the administrator looking at a clock. chronyd can examine the errors corrected at different updates to estimate the rate at which the computer gains or loses time and use this estimate to trim the computer clock subsequently. chronyd provides support to work out the rate of gain or loss of the real-time clock the hardware clock that maintains the time when the computer is turned off. It can use this data when the system boots to set the system time using an adjusted value of the time taken from the real-time clock. This is at time of writing only available in Linux. Things ntpd can do that chronyd cannot do: ntpd fully supports NTP version 4 RFC 5905 including broadcast multicast manycast clients and servers and the orphan mode. It also supports extra authentication schemes based on public-key cryptography RFC 5906. chronyd uses NTP version 3 RFC 1305 which is compatible with version 4. ntpd includes drivers for many reference clocks whereas chronyd relies on other programs for example gpsd to access the data from the reference clocks. 15.1.2. Choosing Between NT P Daemons Chrony should be considered for all systems which are frequently suspended or otherwise intermittently disconnected and reconnected to a network. Mobile and virtual systems for example. The NTP daemon ntpd should be considered for systems which are normally kept permanently on. Systems which are required to use broadcast or multicast IP or to perform authentication of packets with the Autokey protocol should consider using ntpd. Chrony only supports symmetric key authentication using a message authentication code MAC with MD5 SHA1 or stronger hash functions whereas ntpd also supports the Autokey authentication protocol which can make use of the PKI system. Autokey is described in RFC 5906. 15.2. Understanding chrony and Its Configuration 15.2.1. Understanding chronyd The chrony daemon chronyd running in user space makes adjustments to the system clock which is running in the kernel. It does this by consulting external time sources using the NTP protocol when ever network access allows it to do so. When external references are not available chronyd will use the last calculated drift stored in the drift file. It can also be commanded manually to make corrections by chronyc. 15.2.2. Understanding chronyc The chrony daemon chronyd can be controlled by the command line utility chronyc. This utility provides a command prompt which allows entering of a number of commands to make changes to chronyd. The default configuration is for chronyd to only accept commands from a local instance of chronyc but chronyc can be used to alter the configuration so that chronyd will allow external control. chronyc can be run remotely after first configuring chronyd to accept remote connections. The IP addresses allowed to connect to chronyd should be tightly controlled. 15.2.3. Understanding the chrony Configuration Commands Syst em Administ rat ors Guide 250

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The default configuration file for chronyd is /etc/chrony.conf. The -f option can be used to specify an alternate configuration file path. See the chronyd man page for further options. For a complete list of the directives that can be used see http://chrony.tuxfamily.org/manual.htmlConfiguration- file. Below is a selection of configuration options: Comments Comments should be preceded by or allow Optionally specify a host subnet or network from which to allow NTP connections to a machine acting as NTP server. The default is not to allow connections. Examples: 1. allow server1.example.com Use this form to specify a particular host by its host name to be allowed access. 2. allow 192.0.2.0/24 Use this form to specify a particular network to be allowed access. 3. allow 2001:db8::/32 Use this form to specify an IPv6 address to be allowed access. cmdallow This is similar to the allow directive see section allow except that it allows control access rather than NTP client access to a particular subnet or host. By “control access” is meant that chronyc can be run on those hosts and successfully connect to chronyd on this computer. The syntax is identical. There is also a cmddeny all directive with similar behavior to the cmdallow all directive. dumpdir Path to the directory to save the measurement history across restarts of chronyd assuming no changes are made to the system clock behavior whilst it is not running. If this capability is to be used via the dumponexit command in the configuration file or the dump command in chronyc the dumpdir command should be used to define the directory where the measurement histories are saved. dumponexit If this command is present it indicates that chronyd should save the measurement history for each of its time sources recorded whenever the program exits. See the dumpdir command above. local The local keyword is used to allow chronyd to appear synchronized to real time from the viewpoint of clients polling it even if it has no current synchronization source. This option is normally used on the “master” computer in an isolated network where several computers are required to synchronize to one another and the “master” is kept in line with real time by manual input. ⁠Chapt er 1 5. Configuring NT P Using t he chrony Suit e 251

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An example of the command is: local stratum 10 A large value of 10 indicates that the clock is so many hops away from a reference clock that its time is unreliable. If the computer ever has access to another computer which is ultimately synchronized to a reference clock it will almost certainly be at a stratum less than 10. Therefore the choice of a high value like 10 for the local command prevents the machine’s own time from ever being confused with real time were it ever to leak out to clients that have visibility of real servers. log The log command indicates that certain information is to be logged. It accepts the following options: measurements This option logs the raw NTP measurements and related information to a file called measurements.log. statistics This option logs information about the regression processing to a file called statistics.log. tracking This option logs changes to the estimate of the system’s gain or loss rate and any slews made to a file called tracking.log. rtc This option logs information about the system’s real-time clock. refclocks This option logs the raw and filtered reference clock measurements to a file called refclocks.log. tempcomp This option logs the temperature measurements and system rate compensations to a file called tempcomp.log. The log files are written to the directory specified by the logdir command. An example of the command is: log measurements statistics tracking logdir This directive allows the directory where log files are written to be specified. An example of the use of this directive is: logdir /var/log/chrony makestep Syst em Administ rat ors Guide 252

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Normally chronyd will cause the system to gradually correct any time offset by slowing down or speeding up the clock as required. In certain situations the system clock may be so far adrift that this slewing process would take a very long time to correct the system clock. This directive forces chronyd to step system clock if the adjustment is larger than a threshold value but only if there were no more clock updates since chronyd was started than a specified limit a negative value can be used to disable the limit. This is particularly useful when using reference clocks because the initstepslew directive only works with NTP sources. An example of the use of this directive is: makestep 1000 10 This would step the system clock if the adjustment is larger than 1000 seconds but only in the first ten clock updates. maxchange This directive sets the maximum allowed offset corrected on a clock update. The check is performed only after the specified number of updates to allow a large initial adjustment of the system clock. When an offset larger than the specified maximum occurs it will be ignored for the specified number of times and then chronyd will give up and exit a negative value can be used to never exit. In both cases a message is sent to syslog. An example of the use of this directive is: maxchange 1000 1 2 After the first clock update chronyd will check the offset on every clock update it will ignore two adjustments larger than 1000 seconds and exit on another one. maxupdateskew One of chronyds tasks is to work out how fast or slow the computer’s clock runs relative to its reference sources. In addition it computes an estimate of the error bounds around the estimated value. If the range of error is too large it indicates that the measurements have not settled down yet and that the estimated gain or loss rate is not very reliable. The maxupdateskew parameter is the threshold for determining whether an estimate is too unreliable to be used. By default the threshold is 1000 ppm. The format of the syntax is: maxupdateskew skew-in-ppm Typical values for skew-in-ppm might be 100 for a dial-up connection to servers over a telephone line and 5 or 10 for a computer on a LAN. It should be noted that this is not the only means of protection against using unreliable estimates. At all times chronyd keeps track of both the estimated gain or loss rate and the error bound on the estimate. When a new estimate is generated following another measurement from one of the sources a weighted combination algorithm is used to update the master estimate. So if chronyd has an existing highly-reliable master estimate and a new estimate is generated which has large error bounds the existing master estimate will dominate in the new master estimate. noclientlog This directive which takes no arguments specifies that client accesses are not to be logged. Normally they are logged allowing statistics to be reported using the clients command in chronyc. ⁠Chapt er 1 5. Configuring NT P Using t he chrony Suit e 253

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reselectdist When chronyd selects synchronization source from available sources it will prefer the one with minimum synchronization distance. However to avoid frequent reselecting when there are sources with similar distance a fixed distance is added to the distance for sources that are currently not selected. This can be set with the reselectdist option. By default the distance is 100 microseconds. The format of the syntax is: reselectdist dist-in-seconds stratumweight The stratumweight directive sets how much distance should be added per stratum to the synchronization distance when chronyd selects the synchronization source from available sources. The format of the syntax is: stratumweight dist-in-seconds By default dist-in-seconds is 1 second. This means that sources with lower stratum are usually preferred to sources with higher stratum even when their distance is significantly worse. Setting stratumweight to 0 makes chronyd ignore stratum when selecting the source. rtcfile The rtcfile directive defines the name of the file in which chronyd can save parameters associated with tracking the accuracy of the system’s real-time clock RTC. The format of the syntax is: rtcfile /var/lib/chrony/rtc chronyd saves information in this file when it exits and when the writertc command is issued in chronyc. The information saved is the RTC’s error at some epoch that epoch in seconds since January 1 1970 and the rate at which the RTC gains or loses time. Not all real-time clocks are supported as their code is system-specific. Note that if this directive is used then the real-time clock should not be manually adjusted as this would interfere with chronys need to measure the rate at which the real-time clock drifts if it was adjusted at random intervals. rtcsync The rtcsync directive is present in the /etc/chrony.conf file by default. This will inform the kernel the system clock is kept synchronized and the kernel will update the real-time clock every 11 minutes. 15.2.4 . Security with chronyc As access to chronyc allows changing chronyd just as editing the configuration files would access to chronyc should be limited. Passwords can be specified in the key file written in ASCII or HEX to restrict the use of chronyc. One of the entries is used to restrict the use of operational commands and is referred to as the command key. In the default configuration a random command key is generated automatically on start. It should not be necessary to specify or alter it manually. Syst em Administ rat ors Guide 254

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Other entries in the key file can be used as NTP keys to authenticate packets received from remote NTP servers or peers. The two sides need to share a key with identical ID hash type and password in their key file. This requires manually creating the keys and copying them over a secure medium such as SSH. If the key ID was for example 10 then the systems that act as clients must have a line in their configuration files in the following format: server w.x.y.z key 10 peer w.x.y.z key 10 The location of the key file is specified in the /etc/chrony.conf file. The default entry in the configuration file is: keyfile /etc/chrony.keys The command key number is specified in /etc/chrony.conf using the commandkey directive it is the key chronyd will use for authentication of user commands. The directive in the configuration file takes the following form: commandkey 1 An example of the format of the default entry in the key file /etc/chrony.keys for the command key is: 1 SHA1 HEX:A6CFC50C9C93AB6E5A19754C246242FC5471BCDF Where 1 is the key ID SHA1 is the hash function to use HEX is the format of the key and A6CFC50C9C93AB6E5A19754C246242FC5471BCDF is the key randomly generated when chronyd was started for the first time. The key can be given in hexidecimal or ASCII format the default. A manual entry in the key file used to authenticate packets from certain NTP servers or peers can be as simple as the following: 20 foobar Where 20 is the key ID and foobar is the secret authentication key. The default hash is MD5 and ASCII is the default format for the key. By default chronyd is configured to listen for commands only from localhost 127.0.0.1 and ::1 on port 323. To access chronyd remotely with chronyc any bindcmdaddress directives in the /etc/chrony.conf file should be removed to enable listening on all interfaces and the cmdallow directive should be used to allow commands from the remote IP address network or subnet. In addition port 323 has to be opened in the firewall in order to connect from a remote system. Note that the allow directive is for NTP access whereas the cmdallow directive is to enable the receiving of remote commands. It is possible to make these changes temporarily using chronyc running locally. Edit the configuration file to make persistent changes. The communication between chronyc and chronyd is done over UDP so it needs to be authorized before issuing operational commands. To authorize use the authhash and password commands as follows: chronyc authhash SHA1 chronyc password HEX:A6CFC50C9C93AB6E5A19754C246242FC5471BCDF 200 OK ⁠Chapt er 1 5. Configuring NT P Using t he chrony Suit e 255

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If chronyc is used to configure the local chronyd the -a option will run the authhash and password commands automatically. Only the following commands can be used without providing a password: activity authhash dns exit help password quit rtcdata sources sourcestats tracking waitsync . 15.3. Using chrony 15.3.1. Installing chrony The chrony suite is installed by default on some versions of Red Hat Enterprise Linux 7. If required to ensure that it is run the following command as root: yum install chrony The default location for the chrony daemon is /usr/sbin/chronyd. The command line utility will be installed to /usr/bin/chronyc. 15.3.2. Checking the Status of chronyd To check the status of chronyd issue the following command: systemctl status chronyd chronyd.service - NTP client/server Loaded: loaded /usr/lib/systemd/system/chronyd.service enabled Active: active running since Wed 2013-06-12 22:23:16 CEST 11h ago 15.3.3. Starting chronyd To start chronyd issue the following command as root: systemctl start chronyd To ensure chronyd starts automatically at system start issue the following command as root: systemctl enable chronyd 15.3.4 . Stopping chronyd To stop chronyd issue the following command as root: systemctl stop chronyd To prevent chronyd from starting automatically at system start issue the following command as root: systemctl disable chronyd 15.3.5. Checking if chrony is Synchronized Syst em Administ rat ors Guide 256

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To check if chrony is synchronized make use of the tracking sources and sourcestats commands. 15.3.5.1. Checking chro ny T racking To check chrony tracking issue the following command: chronyc tracking Reference ID : 1.2.3.4 a.b.c Stratum : 3 Ref time UTC : Fri Feb 3 15:00:29 2012 System time : 0.000001501 seconds slow of NTP time Last offset : -0.000001632 seconds RMS offset : 0.000002360 seconds Frequency : 331.898 ppm fast Residual freq : 0.004 ppm Skew : 0.154 ppm Root delay : 0.373169 seconds Root dispersion : 0.024780 seconds Update interval : 64.2 seconds Leap status : Normal The fields are as follows: Reference ID This is the reference ID and name or IP address if available of the server to which the computer is currently synchronized. If this is 127.127.1.1 it means the computer is not synchronized to any external source and that you have the “local” mode operating via the local command in chronyc or the local directive in the /etc/chrony.conf file see section local. Stratum The stratum indicates how many hops away from a computer with an attached reference clock we are. Such a computer is a stratum-1 computer so the computer in the example is two hops away that is to say a.b.c is a stratum-2 and is synchronized from a stratum-1. Ref time This is the time UTC at which the last measurement from the reference source was processed. System time In normal operation chronyd never steps the system clock because any jump in the timescale can have adverse consequences for certain application programs. Instead any error in the system clock is corrected by slightly speeding up or slowing down the system clock until the error has been removed and then returning to the system clock’s normal speed. A consequence of this is that there will be a period when the system clock as read by other programs using the gettimeofday system call or by the date command in the shell will be different from chronyds estimate of the current true time which it reports to NTP clients when it is operating in server mode. The value reported on this line is the difference due to this effect. Last offset This is the estimated local offset on the last clock update. ⁠Chapt er 1 5. Configuring NT P Using t he chrony Suit e 257

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RMS offset This is a long-term average of the offset value. Frequency The “frequency” is the rate by which the system’s clock would be wrong if chronyd was not correcting it. It is expressed in ppm parts per million. For example a value of 1ppm would mean that when the system’s clock thinks it has advanced 1 second it has actually advanced by 1.000001 seconds relative to true time. Residual freq This shows the “residual frequency” for the currently selected reference source. This reflects any difference between what the measurements from the reference source indicate the frequency should be and the frequency currently being used. The reason this is not always zero is that a smoothing procedure is applied to the frequency. Each time a measurement from the reference source is obtained and a new residual frequency computed the estimated accuracy of this residual is compared with the estimated accuracy see skew next of the existing frequency value. A weighted average is computed for the new frequency with weights depending on these accuracies. If the measurements from the reference source follow a consistent trend the residual will be driven to zero over time. Skew This is the estimated error bound on the frequency. Root delay This is the total of the network path delays to the stratum-1 computer from which the computer is ultimately synchronized. In certain extreme situations this value can be negative. This can arise in a symmetric peer arrangement where the computers’ frequencies are not tracking each other and the network delay is very short relative to the turn-around time at each computer. Root dispersion This is the total dispersion accumulated through all the computers back to the stratum-1 computer from which the computer is ultimately synchronized. Dispersion is due to system clock resolution statistical measurement variations etc. Leap status This is the leap status which can be Normal Insert second Delete second or Not synchronized. 15.3.5.2. Checking chro ny So urces The sources command displays information about the current time sources that chronyd is accessing. The optional argument -v can be specified meaning verbose. In this case extra caption lines are shown as a reminder of the meanings of the columns. chronyc sources 210 Number of sources 3 MS Name/IP address Stratum Poll Reach LastRx Last sample GPS0 0 4 377 11 -479ns -621ns +/- 134ns Syst em Administ rat ors Guide 258

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a.b.c 2 6 377 23 -923us -924us +/- 43ms + d.e.f 1 6 377 21 -2629us-2619us +/- 86ms The columns are as follows: M This indicates the mode of the source. means a server means a peer and indicates a locally connected reference clock. S This column indicates the state of the sources. “” indicates the source to which chronyd is currently synchronized. “+” indicates acceptable sources which are combined with the selected source. “-” indicates acceptable sources which are excluded by the combining algorithm. “” indicates sources to which connectivity has been lost or whose packets do not pass all tests. “x” indicates a clock which chronyd thinks is a falseticker its time is inconsistent with a majority of other sources. “” indicates a source whose time appears to have too much variability. The “” condition is also shown at start-up until at least 3 samples have been gathered from it. Name/IP address This shows the name or the IP address of the source or reference ID for reference clocks. Stratum This shows the stratum of the source as reported in its most recently received sample. Stratum 1 indicates a computer with a locally attached reference clock. A computer that is synchronized to a stratum 1 computer is at stratum 2. A computer that is synchronized to a stratum 2 computer is at stratum 3 and so on. Poll This shows the rate at which the source is being polled as a base-2 logarithm of the interval in seconds. Thus a value of 6 would indicate that a measurement is being made every 64 seconds. chronyd automatically varies the polling rate in response to prevailing conditions. Reach This shows the source’s reach register printed as an octal number. The register has 8 bits and is updated on every received or missed packet from the source. A value of 377 indicates that a valid reply was received for all of the last eight transmissions. LastRx This column shows how long ago the last sample was received from the source. This is normally in seconds. The letters m h d or y indicate minutes hours days or years. A value of 10 years indicates there were no samples received from this source yet. Last sample This column shows the offset between the local clock and the source at the last measurement. The number in the square brackets shows the actual measured offset. This may be suffixed by ns indicating nanoseconds us indicating microseconds ms indicating milliseconds or s indicating seconds. The number to the left of the square ⁠Chapt er 1 5. Configuring NT P Using t he chrony Suit e 259

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brackets shows the original measurement adjusted to allow for any slews applied to the local clock since. The number following the +/- indicator shows the margin of error in the measurement. Positive offsets indicate that the local clock is ahead of the source. 15.3.5.3. Checking chro ny So urce St at ist ics The sourcestats command displays information about the drift rate and offset estimation process for each of the sources currently being examined by chronyd. The optional argument -v can be specified meaning verbose. In this case extra caption lines are shown as a reminder of the meanings of the columns. chronyc sourcestats 210 Number of sources 1 Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev abc.def.ghi 11 5 46m -0.001 0.045 1us 25us The columns are as follows: Name/IP address This is the name or IP address of the NTP server or peer or reference ID of the reference clock to which the rest of the line relates. NP This is the number of sample points currently being retained for the server. The drift rate and current offset are estimated by performing a linear regression through these points. NR This is the number of runs of residuals having the same sign following the last regression. If this number starts to become too small relative to the number of samples it indicates that a straight line is no longer a good fit to the data. If the number of runs is too low chronyd discards older samples and re-runs the regression until the number of runs becomes acceptable. Span This is the interval between the oldest and newest samples. If no unit is shown the value is in seconds. In the example the interval is 46 minutes. Frequency This is the estimated residual frequency for the server in parts per million. In this case the computer’s clock is estimated to be running 1 part in 10 9 slow relative to the server. Freq Skew This is the estimated error bounds on Freq again in parts per million. Offset This is the estimated offset of the source. Std Dev Syst em Administ rat ors Guide 260

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This is the estimated sample standard deviation. 15.3.6. Manually Adjusting the System Clock To update or step the system clock immediately bypassing any adjustments in progress by slewing the clock issue the following commands as root: chronyc chrony password commandkey-password 200 OK chrony makestep 200 OK Where commandkey-password is the command key or password stored in the key file. If the rtcfile directive is used the real-time clock should not be manually adjusted. Random adjustments would interfere with chronys need to measure the rate at which the real-time clock drifts. If chronyc is used to configure the local chronyd the -a will run the authhash and password commands automatically. This means that the interactive session illustrated above can be replaced by: chronyc -a makestep 15.4. Setting Up chrony for Different Environments 15.4 .1. Setting Up chrony for a System Which is Infrequently Connected This example is intended for systems which use dial-on-demand connections. The normal configuration should be sufficient for mobile and virtual devices which connect intermittently. First review and confirm that the default settings in the /etc/chrony.conf are similar to the following: driftfile /var/lib/chrony/drift commandkey 1 keyfile /etc/chrony.keys The command key ID is generated at install time and should correspond with the commandkey value in the key file /etc/chrony.keys. Using your editor running as root add the addresses of four NTP servers as follows: server 0.pool.ntp.org offline server 1.pool.ntp.org offline server 2.pool.ntp.org offline server 3.pool.ntp.org offline The offline option can be useful in preventing systems from trying to activate connections. The chrony daemon will wait for chronyc to inform it that the system is connected to the network or Internet. 15.4 .2. Setting Up chrony for a System in an Isolated Network For a network that is never connected to the Internet one computer is selected to be the master ⁠Chapt er 1 5. Configuring NT P Using t he chrony Suit e 261

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timeserver. The other computers are either direct clients of the master or clients of clients. On the master the drift file must be manually set with the average rate of drift of the system clock. If the master is rebooted it will obtain the time from surrounding systems and take an average to set its system clock. Thereafter it resumes applying adjustments based on the drift file. The drift file will be updated automatically when the settime command is used. On the system selected to be the master using a text editor running as root edit the /etc/chrony.conf as follows: driftfile /var/lib/chrony/drift commandkey 1 keyfile /etc/chrony.keys initstepslew 10 client1 client3 client6 local stratum 8 manual allow 192.0.2.0 Where 192.0.2.0 is the network or subnet address from which the clients are allowed to connect. On the systems selected to be direct clients of the master using a text editor running as root edit the /etc/chrony.conf as follows: server master driftfile /var/lib/chrony/drift logdir /var/log/chrony log measurements statistics tracking keyfile /etc/chrony.keys commandkey 24 local stratum 10 initstepslew 20 master allow 192.0.2.123 Where 192.0.2.123 is the address of the master and master is the host name of the master. Clients with this configuration will resynchronize the master if it restarts. On the client systems which are not to be direct clients of the master the /etc/chrony.conf file should be the same except that the local and allow directives should be omitted. 15.5. Using chronyc 15.5.1. Using chronyc to Control chronyd To make changes to the local instance of chronyd using the command line utility chronyc in interactive mode enter the following command as root: chronyc -a chronyc must run as root if some of the restricted commands are to be used. The -a option is for automatic authentication using the local keys when configuring chronyd on the local system. See Section 15.2.4 “Security with chronyc” for more information. The chronyc command prompt will be displayed as follows: chronyc Syst em Administ rat ors Guide 262

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You can type help to list all of the commands. The utility can also be invoked in non-interactive command mode if called together with a command as follows: chronyc command Note Changes made using chronyc are not permanent they will be lost after a chronyd restart. For permanent changes modify /etc/chrony.conf. 15.5.2. Using chronyc for Remote Administration To configure chrony to connect to a remote instance of chronyd issue a command in the following format: chronyc -h hostname Where hostname is the host name to connect to. The default is to connect to the local daemon. To configure chrony to connect to a remote instance of chronyd on a non-default port issue a command in the following format: chronyc -h hostname -p port Where port is the port in use for controlling and monitoring by the remote instance of chronyd. Note that commands issued at the chronyc command prompt are not persistent. Only commands in the configuration file are persistent. The first command must be the password command at the chronyc command prompt as follows: chronyc password password 200 OK The password should not have any spaces. If the password is not an MD5 hash the hashed password must be preceded by the authhash command as follows: chronyc authhash SHA1 chronyc password HEX:A6CFC50C9C93AB6E5A19754C246242FC5471BCDF 200 OK The password or hash associated with the command key for a remote system is best obtained by SSH. An SSH connection should be established to the remote machine and the ID of the command key from /etc/chrony.conf and the command key in /etc/chrony.keys memorized or stored securely for the duration of the session. 15.6. Additional Resources ⁠Chapt er 1 5. Configuring NT P Using t he chrony Suit e 263

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The following sources of information provide additional resources regarding chrony. 15.6.1. Installed Documentation chrony1 man page — Introduces the chrony daemon and the command-line interface tool. chronyc1 man page — Describes the chronyc command-line interface tool including commands and command options. chronyd1 man page — Describes the chronyd daemon including commands and command options. chrony.conf5 man page — Describes the chrony configuration file. /usr/share/doc/chrony/chrony.txt — User guide for the chrony suite. 15.6.2. Online Documentation http://chrony.tuxfamily.org/manual.html The online user guide for chrony. Syst em Administ rat ors Guide 264

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Chapter 16. Configuring NTP Using ntpd 16.1. Introduction to NTP The Network Time Protocol NTP enables the accurate dissemination of time and date information in order to keep the time clocks on networked computer systems synchronized to a common reference over the network or the Internet. Many standards bodies around the world have atomic clocks which may be made available as a reference. The satellites that make up the Global Position System contain more than one atomic clock making their time signals potentially very accurate. Their signals can be deliberately degraded for military reasons. An ideal situation would be where each site has a server with its own reference clock attached to act as a site-wide time server. Many devices which obtain the time and date via low frequency radio transmissions or the Global Position System GPS exist. However for most situations a range of publicly accessible time servers connected to the Internet at geographically dispersed locations can be used. These NTP servers provide “Coordinated Universal Time” UTC. Information about these time servers can found at www.pool.ntp.org. Accurate time keeping is important for a number of reasons in IT. In networking for example accurate time stamps in packets and logs are required. Logs are used to investigate service and security issues and so time stamps made on different systems must be made by synchronized clocks to be of real value. As systems and networks become increasingly faster there is a corresponding need for clocks with greater accuracy and resolution. In some countries there are legal obligations to keep accurately synchronized clocks. Please see www.ntp.org for more information. In Linux systems NTP is implemented by a daemon running in user space. The default NTP user space daemon in Red Hat Enterprise Linux 7 is chronyd. It must be disabled if you want to use the ntpd daemon. See Chapter 15 Configuring NTP Using the chrony Suite for information on chrony. The user space daemon updates the system clock which is a software clock running in the kernel. Linux uses a software clock as its system clock for better resolution than the typical embedded hardware clock referred to as the “Real Time Clock” RTC. See the rtc4 and hwclock8 man pages for information on hardware clocks. The system clock can keep time by using various clock sources. Usually the Time Stamp Counter TSC is used. The TSC is a CPU register which counts the number of cycles since it was last reset. It is very fast has a high resolution and there are no interrupts. On system start the system clock reads the time and date from the RTC. The time kept by the RTC will drift away from actual time by up to 5 minutes per month due to temperature variations. Hence the need for the system clock to be constantly synchronized with external time references. When the system clock is being synchronized by ntpd the kernel will in turn update the RTC every 11 minutes automatically. 16.2. NTP Strata NTP servers are classified according to their synchronization distance from the atomic clocks which are the source of the time signals. The servers are thought of as being arranged in layers or strata from 1 at the top down to 15. Hence the word stratum is used when referring to a specific layer. Atomic clocks are referred to as Stratum 0 as this is the source but no Stratum 0 packet is sent on the Internet all stratum 0 atomic clocks are attached to a server which is referred to as stratum 1. These servers send out packets marked as Stratum 1. A server which is synchronized by means of packets marked stratum n belongs to the next lower stratum and will mark its packets as stratum n+1. Servers of the same stratum can exchange packets with each other but are still designated as belonging to just the one stratum the stratum one below the best reference they are synchronized to. The designation Stratum 16 is used to indicate that the server is not currently synchronized to a reliable time source. Note that by default NTP clients act as servers for those systems in the stratum below them. Here is a summary of the NTP Strata: ⁠Chapt er 1 6 . Configuring NT P Using nt pd 265

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Stratum 0: Atomic Clocks and their signals broadcast over Radio and GPS GPS Global Positioning System Mobile Phone Systems Low Frequency Radio Broadcasts WWVB Colorado USA. JJY-40 and JJY-60 Japan DCF77 Germany and MSF United Kingdom These signals can be received by dedicated devices and are usually connected by RS-232 to a system used as an organizational or site-wide time server. Stratum 1: Computer with radio clock GPS clock or atomic clock attached Stratum 2: Reads from stratum 1 Serves to lower strata Stratum 3: Reads from stratum 2 Serves to lower strata Stratum n + 1: Reads from stratum n Serves to lower strata Stratum 15: Reads from stratum 14 This is the lowest stratum. This process continues down to Stratum 15 which is the lowest valid stratum. The label Stratum 16 is used to indicated an unsynchronized state. 16.3. Understanding NTP The version of NTP used by Red Hat Enterprise Linux is as described in RFC 1305 Network Time Protocol Version 3 Specification Implementation and Analysis and RFC 5905 Network Time Protocol Version 4: Protocol and Algorithms Specification This implementation of NTP enables sub-second accuracy to be achieved. Over the Internet accuracy to 10s of milliseconds is normal. On a Local Area Network LAN 1 ms accuracy is possible under ideal conditions. This is because clock drift is now accounted and corrected for which was not done in earlier simpler time protocol systems. A resolution of 233 picoseconds is provided by using 64-bit time stamps. The first 32-bits of the time stamp is used for seconds the last 32-bits are used for fractions of seconds. NTP represents the time as a count of the number of seconds since 00:00 midnight 1 January 1900 GMT. As 32-bits is used to count the seconds this means the time will “roll over” in 2036. However NTP works on the difference between time stamps so this does not present the same level of problem as other implementations of time protocols have done. If a hardware clock that is within 68 years of the correct time is available at boot time then NTP will correctly interpret the current date. The NTP4 specification provides for an “Era Number” and an “Era Offset” which can be used to make software more robust when dealing with time lengths of more than 68 years. Note please do not confuse this with the Unix Year 2038 problem. Syst em Administ rat ors Guide 266

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The NTP protocol provides additional information to improve accuracy. Four time stamps are used to allow the calculation of round-trip time and server response time. In order for a system in its role as NTP client to synchronize with a reference time server a packet is sent with an “originate time stamp”. When the packet arrives the time server adds a “receive time stamp”. After processing the request for time and date information and just before returning the packet it adds a “transmit time stamp”. When the returning packet arrives at the NTP client a “receive time stamp” is generated. The client can now calculate the total round trip time and by subtracting the processing time derive the actual traveling time. By assuming the outgoing and return trips take equal time the single-trip delay in receiving the NTP data is calculated. The full NTP algorithm is much more complex than presented here. When a packet containing time information is received it is not immediately responded to but is first subject to validation checks and then processed together with several other time samples to arrive at an estimate of the time. This is then compared to the system clock to determine the time offset the difference between the system clocks time and what ntpd has determined the time should be. The system clock is adjusted slowly at most at a rate of 0.5ms per second to reduce this offset by changing the frequency of the counter being used. It will take at least 2000 seconds to adjust the clock by 1 second using this method. This slow change is referred to as slewing and cannot go backwards. If the time offset of the clock is more than 128ms the default setting ntpd can “step” the clock forwards or backwards. If the time offset at system start is greater than 1000 seconds then the user or an installation script should make a manual adjustment. See Chapter 2 Configuring the Date and Time. With the -g option to the ntpd command used by default any offset at system start will be corrected but during normal operation only offsets of up to 1000 seconds will be corrected. Some software may fail or produce an error if the time is changed backwards. For systems that are sensitive to step changes in the time the threshold can be changed to 600s instead of 128ms using the -x option unrelated to the -g option. Using the -x option to increase the stepping limit from 0.128s to 600s has a drawback because a different method of controlling the clock has to be used. It disables the kernel clock discipline and may have a negative impact on the clock accuracy. The -x option can be added to the /etc/sysconfig/ntpd configuration file. 16.4. Understanding the Drift File The drift file is used to store the frequency offset between the system clock running at its nominal frequency and the frequency required to remain in synchronization with UTC. If present the value contained in the drift file is read at system start and used to correct the clock source. Use of the drift file reduces the time required to achieve a stable and accurate time. The value is calculated and the drift file replaced once per hour by ntpd. The drift file is replaced rather than just updated and for this reason the drift file must be in a directory for which the ntpd has write permissions. 16.5. UTC Timezones and DST As NTP is entirely in UTC Universal Time Coordinated Timezones and DST Daylight Saving Time are applied locally by the system. The file /etc/localtime is a copy of or symlink to a zone information file from /usr/share/zoneinfo. The RTC may be in localtime or in UTC as specified by the 3rd line of /etc/adjtime which will be one of LOCAL or UTC to indicate how the RTC clock has been set. Users can easily change this setting using the checkbox System Clock Uses UTC in the Date and Time graphical configuration tool. See Chapter 2 Configuring the Date and Time for information on how to use that tool. Running the RTC in UTC is recommended to avoid various problems when daylight saving time is changed. The operation of ntpd is explained in more detail in the man page ntpd8. The resources section lists useful sources of information. See Section 16.20 “Additional Resources”. 16.6. Authentication Options for NTP ⁠Chapt er 1 6 . Configuring NT P Using nt pd 267

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NTPv4 added support for the Autokey Security Architecture which is based on public asymmetric cryptography while retaining support for symmetric key cryptography. The Autokey Security Architecture is described in RFC 5906 Network Time Protocol Version 4: Autokey Specification. The man page ntp_auth5 describes the authentication options and commands for ntpd. An attacker on the network can attempt to disrupt a service by sending NTP packets with incorrect time information. On systems using the public pool of NTP servers this risk is mitigated by having more than three NTP servers in the list of public NTP servers in /etc/ntp.conf. If only one time source is compromised or spoofed ntpd will ignore that source. You should conduct a risk assessment and consider the impact of incorrect time on your applications and organization. If you have internal time sources you should consider steps to protect the network over which the NTP packets are distributed. If you conduct a risk assessment and conclude that the risk is acceptable and the impact to your applications minimal then you can choose not to use authentication. The broadcast and multicast modes require authentication by default. If you have decided to trust the network then you can disable authentication by using disable auth directive in the ntp.conf file. Alternatively authentication needs to be configured by using SHA1 or MD5 symmetric keys or by public asymmetric key cryptography using the Autokey scheme. The Autokey scheme for asymmetric cryptography is explained in the ntp_auth8 man page and the generation of keys is explained in ntp-keygen8. To implement symmetric key cryptography see Section 16.17.12 “Configuring Symmetric Authentication Using a Key” for an explanation of the key option. 16.7. Managing the Time on Virtual Machines Virtual machines cannot access a real hardware clock and a virtual clock is not stable enough as the stability is dependent on the host systems work load. For this reason para-virtualized clocks should be provided by the virtualization application in use. On Red Hat Enterprise Linux with KVM the default clock source is kvm-clock. See the KVM guest timing management chapter of the Red Hat Enterprise Linux 7 Virtualization Deployment and Administration Guide. 16.8. Understanding Leap Seconds Greenwich Mean Time GMT was derived by measuring the solar day which is dependent on the Earths rotation. When atomic clocks were first made the potential for more accurate definitions of time became possible. In 1958 International Atomic Time TAI was introduced based on the more accurate and very stable atomic clocks. A more accurate astronomical time Universal Time 1 UT1 was also introduced to replace GMT. The atomic clocks are in fact far more stable than the rotation of the Earth and so the two times began to drift apart. For this reason UTC was introduced as a practical measure. It is kept within one second of UT1 but to avoid making many small trivial adjustments it was decided to introduce the concept of a leap second in order to reconcile the difference in a manageable way. The difference between UT1 and UTC is monitored until they drift apart by more than half a second. Then only is it deemed necessary to introduce a one second adjustment forward or backward. Due to the erratic nature of the Earths rotational speed the need for an adjustment cannot be predicted far into the future. The decision as to when to make an adjustment is made by the International Earth Rotation and Reference Systems Service IERS. However these announcements are important only to administrators of Stratum 1 servers because NTP transmits information about pending leap seconds and applies them automatically. 16.9. Understanding the ntpd Configuration File The daemon ntpd reads the configuration file at system start or when the service is restarted. The default location for the file is /etc/ntp.conf and you can view the file by entering the following command: Syst em Administ rat ors Guide 268

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less /etc/ntp.conf The configuration commands are explained briefly later in this chapter see Section 16.17 “Configure NTP” and more verbosely in the ntp.conf5 man page. Here follows a brief explanation of the contents of the default configuration file: The driftfile entry A path to the drift file is specified the default entry on Red Hat Enterprise Linux is: driftfile /var/lib/ntp/drift If you change this be certain that the directory is writable by ntpd. The file contains one value used to adjust the system clock frequency after every system or service start. See Understanding the Drift File for more information. The access control entries The following line sets the default access control restriction: restrict default nomodify notrap nopeer noquery The nomodify options prevents any changes to the configuration. The notrap option prevents ntpdc control message protocol traps. The nopeer option prevents a peer association being formed. The noquery option prevents ntpq and ntpdc queries but not time queries from being answered. Important The ntpq and ntpdc queries can be used in amplification attacks therefore do not remove the noquery option from the restrict default command on publicly accessible systems. See CVE-2013-5211 for more details. Addresses within the range 127.0.0.0/8 are sometimes required by various processes or applications. As the "restrict default" line above prevents access to everything not explicitly allowed access to the standard loopback address for IPv4 and IPv6 is permitted by means of the following lines: the administrative functions. restrict 127.0.0.1 restrict ::1 Addresses can be added underneath if specifically required by another application. Hosts on the local network are not permitted because of the "restrict default" line above. To change this for example to allow hosts from the 192.0.2.0/24 network to query the time and statistics but nothing more a line in the following format is required: ⁠Chapt er 1 6 . Configuring NT P Using nt pd 269

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restrict 192.0.2.0 mask 255.255.255.0 nomodify notrap nopeer To allow unrestricted access from a specific host for example 192.0.2.250/32 a line in the following format is required: restrict 192.0.2.250 A mask of 255.255.255.255 is applied if none is specified. The restrict commands are explained in the ntp_acc5 man page. The public servers entry By default the ntp.conf file contains four public server entries: server 0.rhel.pool.ntp.org iburst server 1.rhel.pool.ntp.org iburst server 2.rhel.pool.ntp.org iburst server 3.rhel.pool.ntp.org iburst The broadcast multicast servers entry By default the ntp.conf file contains some commented out examples. These are largely self explanatory. See Section 16.17 “Configure NTP” for the explanation of the specific commands. If required add your commands just below the examples. Note When the DHCP client program dhclient receives a list of NTP servers from the DHCP server it adds them to ntp.conf and restarts the service. To disable that feature add PEERNTPno to /etc/sysconfig/network. 16.10. Understanding the ntpd Sysconfig File The file will be read by the ntpd init script on service start. The default contents is as follows: Command line options for ntpd OPTIONS"-g" The -g option enables ntpd to ignore the offset limit of 1000s and attempt to synchronize the time even if the offset is larger than 1000s but only on system start. Without that option ntpd will exit if the time offset is greater than 1000s. It will also exit after system start if the service is restarted and the offset is greater than 1000s even with the -g option. 16.11. Disabling chrony In order to use ntpd the default user space daemon chronyd must be stopped and disabled. Issue the following command as root: systemctl stop chronyd Syst em Administ rat ors Guide 270

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To prevent it restarting at system start issue the following command as root: systemctl disable chronyd To check the status of chronyd issue the following command: systemctl status chronyd 16.12. Checking if the NTP Daemon is Installed To check if ntpd is installed enter the following command as root: yum install ntp NTP is implemented by means of the daemon or service ntpd which is contained within the ntp package. 16.13. Installing the NTP Daemon ntpd To install ntpd enter the following command as root: yum install ntp To enable ntpd at system start enter the following command as root: systemctl enable ntpd 16.14. Checking the Status of NTP To check if ntpd is running and configured to run at system start issue the following command: systemctl status ntpd To obtain a brief status report from ntpd issue the following command: ntpstat unsynchronised time server re-starting polling server every 64 s ntpstat synchronised to NTP server 10.5.26.10 at stratum 2 time correct to within 52 ms polling server every 1024 s 16.15. Configure the Firewall to Allow Incoming NTP Packets ⁠Chapt er 1 6 . Configuring NT P Using nt pd 271

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The NTP traffic consists of UDP packets on port 123 and needs to be permitted through network and host-based firewalls in order for NTP to function. Check if the firewall is configured to allow incoming NTP traffic for clients using the graphical Firewall Configuration tool. To start the graphical firewall-config tool press the Super key to enter the Activities Overview type firewall and then press Enter. The Firewall Configuration window opens. You will be prompted for your user password. To start the graphical firewall configuration tool using the command line enter the following command as root user: firewall-config The Firewall Configuration window opens. Note this command can be run as normal user but you will then be prompted for the root password from time to time. Look for the word “Connected” in the lower left corner. This indicates that the firewall-config tool is connected to the user space daemon firewalld. 16.15.1. Change the Firewall Settings To immediately change the current firewall settings ensure the drop-down selection menu labeled Configuration is set to Runtime. Alternatively to edit the settings to be applied at the next system start or firewall reload select Permanent from the drop-down list. Note When making changes to the firewall settings in Runtime mode your selection takes immediate effect when you set or clear the check box associated with the service. You should keep this in mind when working on a system that may be in use by other users. When making changes to the firewall settings in Permanent mode your selection will only take effect when you reload the firewall or the system restarts. To reload the firewall select the Options menu and select Reload Firewall. 16.15.2. Open Ports in the Firewall for NT P Packets To permit traffic through the firewall to a certain port start the firewall-config tool and select the network zone whose settings you want to change. Select the Ports tab and then click the Add button. The Port and Protocol window opens. Enter the port number 123 and select udp from the drop-down list. 16.16. Configure ntpdate Servers The purpose of the ntpdate service is to set the clock during system boot. This was used previously to ensure that the services started after ntpdate would have the correct time and not observe a jump in the clock. The use of ntpdate and the list of step-tickers is considered deprecated and so Red Hat Enterprise Linux 7 uses the -g option to the ntpd command and not ntpdate by default. Syst em Administ rat ors Guide 272

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The ntpdate service in Red Hat Enterprise Linux 7 is mostly useful only when used alone without ntpd. With systemd which starts services in parallel enabling the ntpdate service will not ensure that other services started after it will have correct time unless they specify an ordering dependency on time-sync.target which is provided by the ntpdate service. In order to ensure a service starts with correct time add Aftertime-sync.target to the service and enable one of the services which provide the target ntpdate or sntp. Some services on Red Hat Enterprise Linux 7 have the dependency included by default for example dhcpd dhcpd6 and crond. To check if the ntpdate service is enabled to run at system start issue the following command: systemctl status ntpdate To enable the service to run at system start issue the following command as root: systemctl enable ntpdate In Red Hat Enterprise Linux 7 the default /etc/ntp/step-tickers file contains 0.rhel.pool.ntp.org. To configure additional ntpdate servers using a text editor running as root edit /etc/ntp/step-tickers. The number of servers listed is not very important as ntpdate will only use this to obtain the date information once when the system is starting. If you have an internal time server then use that host name for the first line. An additional host on the second line as a backup is sensible. The selection of backup servers and whether the second host is internal or external depends on your risk assessment. For example what is the chance of any problem affecting the first server also affecting the second server Would connectivity to an external server be more likely to be available than connectivity to internal servers in the event of a network failure disrupting access to the first server 16.17. Configure NTP To change the default configuration of the NTP service use a text editor running as root user to edit the /etc/ntp.conf file. This file is installed together with ntpd and is configured to use time servers from the Red Hat pool by default. The man page ntp.conf5 describes the command options that can be used in the configuration file apart from the access and rate limiting commands which are explained in the ntp_acc5 man page. 16.17.1. Configure Access Control to an NT P Service To restrict or control access to the NTP service running on a system make use of the restrict command in the ntp.conf file. See the commented out example: Hosts on local network are less restricted. restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap The restrict command takes the following form: restrict option where option is one or more of: ignore — All packets will be ignored including ntpq and ntpdc queries. kod — a “Kiss-o-death” packet is to be sent to reduce unwanted queries. ⁠Chapt er 1 6 . Configuring NT P Using nt pd 273

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limited — do not respond to time service requests if the packet violates the rate limit default values or those specified by the discard command. ntpq and ntpdc queries are not affected. For more information on the discard command and the default values see Section 16.17.2 “Configure Rate Limiting Access to an NTP Service”. lowpriotrap — traps set by matching hosts to be low priority. nomodify — prevents any changes to the configuration. noquery — prevents ntpq and ntpdc queries but not time queries from being answered. nopeer — prevents a peer association being formed. noserve — deny all packets except ntpq and ntpdc queries. notrap — prevents ntpdc control message protocol traps. notrust — deny packets that are not cryptographically authenticated. ntpport — modify the match algorithm to only apply the restriction if the source port is the standard NTP UDP port 123. version — deny packets that do not match the current NTP version. To configure rate limit access to not respond at all to a query the respective restrict command has to have the limited option. If ntpd should reply with a KoD packet the restrict command needs to have both limited and kod options. The ntpq and ntpdc queries can be used in amplification attacks see CVE-2013-5211 for more details do not remove the noquery option from the restrict default command on publicly accessible systems. 16.17.2. Configure Rate Limiting Access to an NT P Service To enable rate limiting access to the NTP service running on a system add the limited option to the restrict command as explained in Section 16.17.1 “Configure Access Control to an NTP Service”. If you do not want to use the default discard parameters then also use the discard command as explained here. The discard command takes the following form: discard average value minimum value monitor value average — specifies the minimum average packet spacing to be permitted it accepts an argument in log 2 seconds. The default value is 3 2 3 equates to 8 seconds. minimum — specifies the minimum packet spacing to be permitted it accepts an argument in log 2 seconds. The default value is 1 2 1 equates to 2 seconds. monitor — specifies the discard probability for packets once the permitted rate limits have been exceeded. The default value is 3000 seconds. This option is intended for servers that receive 1000 or more requests per second. Examples of the discard command are as follows: discard average 4 Syst em Administ rat ors Guide 274

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discard average 4 minimum 2 16.17.3. Adding a Peer Address To add the address of a peer that is to say the address of a server running an NTP service of the same stratum make use of the peer command in the ntp.conf file. The peer command takes the following form: peer address where address is an IP unicast address or a DNS resolvable name. The address must only be that of a system known to be a member of the same stratum. Peers should have at least one time source that is different to each other. Peers are normally systems under the same administrative control. 16.17.4 . Adding a Server Address To add the address of a server that is to say the address of a server running an NTP service of a higher stratum make use of the server command in the ntp.conf file. The server command takes the following form: server address where address is an IP unicast address or a DNS resolvable name. The address of a remote reference server or local reference clock from which packets are to be received. 16.17.5. Adding a Broadcast or Multicast Server Address To add a broadcast or multicast address for sending that is to say the address to broadcast or multicast NTP packets to make use of the broadcast command in the ntp.conf file. The broadcast and multicast modes require authentication by default. See Section 16.6 “Authentication Options for NTP”. The broadcast command takes the following form: broadcast address where address is an IP broadcast or multicast address to which packets are sent. This command configures a system to act as an NTP broadcast server. The address used must be a broadcast or a multicast address. Broadcast address implies the IPv4 address 255.255.255.255. By default routers do not pass broadcast messages. The multicast address can be an IPv4 Class D address or an IPv6 address. The IANA has assigned IPv4 multicast address 224.0.1.1 and IPv6 address FF05::101 site local to NTP. Administratively scoped IPv4 multicast addresses can also be used as described in RFC 2365 Administratively Scoped IP Multicast. 16.17.6. Adding a Manycast Client Address To add a manycast client address that is to say to configure a multicast address to be used for NTP server discovery make use of the manycastclient command in the ntp.conf file. ⁠Chapt er 1 6 . Configuring NT P Using nt pd 275

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The manycastclient command takes the following form: manycastclient address where address is an IP multicast address from which packets are to be received. The client will send a request to the address and select the best servers from the responses and ignore other servers. NTP communication then uses unicast associations as if the discovered NTP servers were listed in ntp.conf. This command configures a system to act as an NTP client. Systems can be both client and server at the same time. 16.17.7. Adding a Broadcast Client Address To add a broadcast client address that is to say to configure a broadcast address to be monitored for broadcast NTP packets make use of the broadcastclient command in the ntp.conf file. The broadcastclient command takes the following form: broadcastclient Enables the receiving of broadcast messages. Requires authentication by default. See Section 16.6 “Authentication Options for NTP”. This command configures a system to act as an NTP client. Systems can be both client and server at the same time. 16.17.8. Adding a Manycast Server Address To add a manycast server address that is to say to configure an address to allow the clients to discover the server by multicasting NTP packets make use of the manycastserver command in the ntp.conf file. The manycastserver command takes the following form: manycastserver address Enables the sending of multicast messages. Where address is the address to multicast to. This should be used together with authentication to prevent service disruption. This command configures a system to act as an NTP server. Systems can be both client and server at the same time. 16.17.9. Adding a Multicast Client Address To add a multicast client address that is to say to configure a multicast address to be monitored for multicast NTP packets make use of the multicastclient command in the ntp.conf file. The multicastclient command takes the following form: multicastclient address Enables the receiving of multicast messages. Where address is the address to subscribe to. This should be used together with authentication to prevent service disruption. Syst em Administ rat ors Guide 276

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This command configures a system to act as an NTP client. Systems can be both client and server at the same time. 16.17.10. Configuring the Burst Option Using the burst option against a public server is considered abuse. Do not use this option with public NTP servers. Use it only for applications within your own organization. To increase the average quality of time offset statistics add the following option to the end of a server command: burst At every poll interval when the server responds the system will send a burst of up to eight packets instead of the usual one packet. For use with the server command to improve the average quality of the time-offset calculations. 16.17.11. Configuring the iburst Option To improve the time taken for initial synchronization add the following option to the end of a server command: iburst When the server is unreachable send a burst of eight packets instead of the usual one packet. The packet spacing is normally 2 s however the spacing between the first and second packets can be changed with the calldelay command to allow additional time for a modem or ISDN call to complete. For use with the server command to reduce the time taken for initial synchronization. This is now a default option in the configuration file. 16.17.12. Configuring Symmetric Authentication Using a Key To configure symmetric authentication using a key add the following option to the end of a server or peer command: key number where number is in the range 1 to 65534 inclusive. This option enables the use of a message authentication code MAC in packets. This option is for use with the peer server broadcast and manycastclient commands. The option can be used in the /etc/ntp.conf file as follows: server 192.168.1.1 key 10 broadcast 192.168.1.255 key 20 manycastclient 239.255.254.254 key 30 See also Section 16.6 “Authentication Options for NTP”. 16.17.13. Configuring the Poll Interval To change the default poll interval add the following options to the end of a server or peer command: ⁠Chapt er 1 6 . Configuring NT P Using nt pd 277

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minpoll value and maxpoll value Options to change the default poll interval where the interval in seconds will be calculated by raising 2 to the power of value in other words the interval is expressed in log 2 seconds. The default minpoll value is 6 2 6 equates to 64s. The default value for maxpoll is 10 which equates to 1024s. Allowed values are in the range 3 to 17 inclusive which equates to 8s to 36.4h respectively. These options are for use with the peer or server. Setting a shorter maxpoll may improve clock accuracy. 16.17.14 . Configuring Server Preference To specify that a particular server should be preferred above others of similar statistical quality add the following option to the end of a server or peer command: prefer Use this server for synchronization in preference to other servers of similar statistical quality. This option is for use with the peer or server commands. 16.17.15. Configuring the T ime-to-Live for NT P Packets To specify that a particular time-to-live TTL value should be used in place of the default add the following option to the end of a server or peer command: ttl value Specify the time-to-live value to be used in packets sent by broadcast servers and multicast NTP servers. Specify the maximum time-to-live value to use for the “expanding ring search” by a manycast client. The default value is 127. 16.17.16. Configuring the NT P Version to Use To specify that a particular version of NTP should be used in place of the default add the following option to the end of a server or peer command: version value Specify the version of NTP set in created NTP packets. The value can be in the range 1 to 4. The default is 4. 16.18. Configuring the Hardware Clock Update The system clock can be used to update the hardware clock also known as the real-time clock RTC. This section shows three approaches to the task: Instant one-time update To perform an instant one-time update of the hardware clock run this command as root: hwclock --systohc Update on every boot Syst em Administ rat ors Guide 278

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To make the hardware clock update on every boot after executing the ntpdate synchronization utility do the following: 1. Add the following line to the /etc/sysconfig/ntpdate file: SYNC_HWCLOCKyes 2. Enable the ntpdate service as root: systemctl enable ntpdate.service Note that the ntpdate service uses the NTP servers defined in the /etc/ntp/step- tickers file. Note On virtual machines the hardware clock will be updated on the next boot of the host machine not of the virtual machine. Update via NTP To make the hardware clock update every time the system clock is updated by the ntpd or chronyd service start the ntpdate service as root: systemctl start ntpdate.service To make the behavior persistent across boots make the service start automatically at the boot time: systemctl enable ntpdate.service As a result of enabling the ntpdate service every time the system clock is synchronized by ntpd or chronyd the kernel automatically updates the hardware clock in 11 minutes. Warning This approach might not always work because the above mentioned 11-minute mode is not always enabled. As a consequence the hardware clock does not necessarily get updated on the system clock update. 16.19. Configuring Clock Sources To list the available clock sources on your system issue the following commands: cd /sys/devices/system/clocksource/clocksource0/ clocksource0 cat available_clocksource kvm-clock tsc hpet acpi_pm clocksource0 cat current_clocksource kvm-clock ⁠Chapt er 1 6 . Configuring NT P Using nt pd 279

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In the above example the kernel is using kvm-clock. This was selected at boot time as this is a virtual machine. Note that the available clock source is architecture dependent. To override the default clock source append the clocksource directive to the end of the kernels GRUB menu entry. Use the grubby tool to make the change. For example to force the default kernel on a system to use the tsc clock source enter a command as follows: grubby --argsclocksourcetsc --update-kernelDEFAULT The --update-kernel parameter also accepts the keyword ALL or a comma separated list of kernel index numbers. See Chapter 24 Working with the GRUB 2 Boot Loader for more information on making changes to the GRUB menu. 16.20. Additional Resources The following sources of information provide additional resources regarding NTP and ntpd. 16.20.1. Installed Documentation ntpd8 man page — Describes ntpd in detail including the command-line options. ntp.conf5 man page — Contains information on how to configure associations with servers and peers. ntpq8 man page — Describes the NTP query utility for monitoring and querying an NTP server. ntpdc8 man page — Describes the ntpd utility for querying and changing the state of ntpd. ntp_auth5 man page — Describes authentication options commands and key management for ntpd. ntp_keygen8 man page — Describes generating public and private keys for ntpd. ntp_acc5 man page — Describes access control options using the restrict command. ntp_mon5 man page — Describes monitoring options for the gathering of statistics. ntp_clock5 man page — Describes commands for configuring reference clocks. ntp_misc5 man page — Describes miscellaneous options. ntp_decode5 man page — Lists the status words event messages and error codes used for ntpd reporting and monitoring. ntpstat8 man page — Describes a utility for reporting the synchronization state of the NTP daemon running on the local machine. ntptime8 man page — Describes a utility for reading and setting kernel time variables. tickadj8 man page — Describes a utility for reading and optionally setting the length of the tick. 16.20.2. Useful Websites Syst em Administ rat ors Guide 280

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http://doc.ntp.org/ The NTP Documentation Archive http://www.eecis.udel.edu/ mills/ntp.html Network Time Synchronization Research Project. http://www.eecis.udel.edu/ mills/ntp/html/manyopt.html Information on Automatic Server Discovery in NTPv4. ⁠Chapt er 1 6 . Configuring NT P Using nt pd 281

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Chapter 17. Configuring PTP Using ptp4l 17.1. Introduction to PTP The Precision Time Protocol PTP is a protocol used to synchronize clocks in a network. When used in conjunction with hardware support PTP is capable of sub-microsecond accuracy which is far better than is normally obtainable with NTP. PTP support is divided between the kernel and user space. The kernel in Red Hat Enterprise Linux includes support for PTP clocks which are provided by network drivers. The actual implementation of the protocol is known as linuxptp a PTPv2 implementation according to the IEEE standard 1588 for Linux. The linuxptp package includes the ptp4 l and phc2sys programs for clock synchronization. The ptp4 l program implements the PTP boundary clock and ordinary clock. With hardware time stamping it is used to synchronize the PTP hardware clock to the master clock and with software time stamping it synchronizes the system clock to the master clock. The phc2sys program is needed only with hardware time stamping for synchronizing the system clock to the PTP hardware clock on the network interface card NIC. 17.1.1. Understanding PT P The clocks synchronized by PTP are organized in a master-slave hierarchy. The slaves are synchronized to their masters which may be slaves to their own masters. The hierarchy is created and updated automatically by the best master clock BMC algorithm which runs on every clock. When a clock has only one port it can be master or slave such a clock is called an ordinary clock OC. A clock with multiple ports can be master on one port and slave on another such a clock is called a boundary clock BC. The top-level master is called the grandmaster clock which can be synchronized by using a Global Positioning System GPS time source. By using a GPS-based time source disparate networks can be synchronized with a high-degree of accuracy. Syst em Administ rat ors Guide 282

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Figure 17.1. PTP grandmaster boundary and slave Clocks 17.1.2. Advantages of PT P One of the main advantages that PTP has over the Network Time Protocol NTP is hardware support present in various network interface controllers NIC and network switches. This specialized hardware allows PTP to account for delays in message transfer and greatly improves the accuracy of time synchronization. While it is possible to use non-PTP enabled hardware components within the network this will often cause an increase in jitter or introduce an asymmetry in the delay resulting in synchronization inaccuracies which add up with multiple non-PTP aware components used in the communication path. To achieve the best possible accuracy it is recommended that all networking components between PTP clocks are PTP hardware enabled. Time synchronization in larger networks where not all of the networking hardware supports PTP might be better suited for NTP. With hardware PTP support the NIC has its own on-board clock which is used to time stamp the received and transmitted PTP messages. It is this on-board clock that is synchronized to the PTP master and the computers system clock is synchronized to the PTP hardware clock on the NIC. With software PTP support the system clock is used to time stamp the PTP messages and it is ⁠Chapt er 1 7 . Configuring PT P Using pt p4 l 283

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synchronized to the PTP master directly. Hardware PTP support provides better accuracy since the NIC can time stamp the PTP packets at the exact moment they are sent and received while software PTP support requires additional processing of the PTP packets by the operating system. 17.2. Using PTP In order to use PTP the kernel network driver for the intended interface has to support either software or hardware time stamping capabilities. 17.2.1. Checking for Driver and Hardware Support In addition to hardware time stamping support being present in the driver the NIC must also be capable of supporting this functionality in the physical hardware. The best way to verify the time stamping capabilities of a particular driver and NIC is to use the ethtool utility to query the interface as follows: ethtool -T eth3 Time stamping parameters for eth3: Capabilities: hardware-transmit SOF_TIMESTAMPING_TX_HARDWARE software-transmit SOF_TIMESTAMPING_TX_SOFTWARE hardware-receive SOF_TIMESTAMPING_RX_HARDWARE software-receive SOF_TIMESTAMPING_RX_SOFTWARE software-system-clock SOF_TIMESTAMPING_SOFTWARE hardware-raw-clock SOF_TIMESTAMPING_RAW_HARDWARE PTP Hardware Clock: 0 Hardware Transmit Timestamp Modes: off HWTSTAMP_TX_OFF on HWTSTAMP_TX_ON Hardware Receive Filter Modes: none HWTSTAMP_FILTER_NONE all HWTSTAMP_FILTER_ALL Where eth3 is the interface you want to check. For software time stamping support the parameters list should include: SOF_TIMESTAMPING_SOFTWARE SOF_TIMESTAMPING_TX_SOFTWARE SOF_TIMESTAMPING_RX_SOFTWARE For hardware time stamping support the parameters list should include: SOF_TIMESTAMPING_RAW_HARDWARE SOF_TIMESTAMPING_TX_HARDWARE SOF_TIMESTAMPING_RX_HARDWARE 17.2.2. Installing PT P The kernel in Red Hat Enterprise Linux includes support for PTP. User space support is provided by the tools in the linuxptp package. To install linuxptp issue the following command as root: Syst em Administ rat ors Guide 284

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yum install linuxptp This will install ptp4 l and phc2sys. Do not run more than one service to set the system clocks time at the same time. If you intend to serve PTP time using NTP see Section 17.8 “Serving PTP Time with NTP”. 17.2.3. Starting ptp4 l The ptp4 l program can be started from the command line or it can be started as a service. When running as a service options are specified in the /etc/sysconfig/ptp4l file. Options required for use both by the service and on the command line should be specified in the /etc/ptp4l.conf file. The /etc/sysconfig/ptp4l file includes the -f /etc/ptp4l.conf command line option which causes the ptp4l program to read the /etc/ptp4l.conf file and process the options it contains. The use of the /etc/ptp4l.conf is explained in Section 17.4 “Specifying a Configuration File”. More information on the different ptp4 l options and the configuration file settings can be found in the ptp4l8 man page. St art ing pt p4l as a Service To start ptp4 l as a service issue the following command as root: systemctl start ptp4l For more information on managing system services in Red Hat Enterprise Linux 7 see Chapter 9 Managing Services with systemd. Using pt p4l Fro m T he Co mmand Line The ptp4 l program tries to use hardware time stamping by default. To use ptp4 l with hardware time stamping capable drivers and NICs you must provide the network interface to use with the -i option. Enter the following command as root: ptp4l -i eth3 -m Where eth3 is the interface you want to configure. Below is example output from ptp4 l when the PTP clock on the NIC is synchronized to a master: ptp4l -i eth3 -m selected eth3 as PTP clock port 1: INITIALIZING to LISTENING on INITIALIZE port 0: INITIALIZING to LISTENING on INITIALIZE port 1: new foreign master 00a069.fffe.0b552d-1 selected best master clock 00a069.fffe.0b552d port 1: LISTENING to UNCALIBRATED on RS_SLAVE master offset -23947 s0 freq +0 path delay 11350 master offset -28867 s0 freq +0 path delay 11236 master offset -32801 s0 freq +0 path delay 10841 master offset -37203 s1 freq +0 path delay 10583 master offset -7275 s2 freq -30575 path delay 10583 port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED master offset -4552 s2 freq -30035 path delay 10385 The master offset value is the measured offset from the master in nanoseconds. The s0 s1 s2 ⁠Chapt er 1 7 . Configuring PT P Using pt p4 l 285

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strings indicate the different clock servo states: s0 is unlocked s1 is clock step and s2 is locked. Once the servo is in the locked state s2 the clock will not be stepped only slowly adjusted unless the pi_offset_const option is set to a positive value in the configuration file described in the ptp4l8 man page. The adj value is the frequency adjustment of the clock in parts per billion ppb. The path delay value is the estimated delay of the synchronization messages sent from the master in nanoseconds. Port 0 is a Unix domain socket used for local PTP management. Port 1 is the eth3 interface based on the example above. INITIALIZING LISTENING UNCALIBRATED and SLAVE are some of possible port states which change on the INITIALIZE RS_SLAVE MASTER_CLOCK_SELECTED events. In the last state change message the port state changed from UNCALIBRATED to SLAVE indicating successful synchronization with a PTP master clock. Lo gging Messages Fro m pt p4l By default messages are sent to /var/log/messages. However specifying the -m option enables logging to standard output which can be useful for debugging purposes. To enable software time stamping the -S option needs to be used as follows: ptp4l -i eth3 -m -S 17.2.3.1. Select ing a Delay Measurement Mechanism There are two different delay measurement mechanisms and they can be selected by means of an option added to the ptp4l command as follows: -P The -P selects the peer-to-peer P2P delay measurement mechanism. The P2P mechanism is preferred as it reacts to changes in the network topology faster and may be more accurate in measuring the delay than other mechanisms. The P2P mechanism can only be used in topologies where each port exchanges PTP messages with at most one other P2P port. It must be supported and used by all hardware including transparent clocks on the communication path. -E The -E selects the end-to-end E2E delay measurement mechanism. This is the default. The E2E mechanism is also referred to as the delay “request-response” mechanism. -A The -A enables automatic selection of the delay measurement mechanism. The automatic option starts ptp4 l in E2E mode. It will change to P2P mode if a peer delay request is received. Note All clocks on a single PTP communication path must use the same mechanism to measure the delay. Warnings will be printed in the following circumstances: When a peer delay request is received on a port using the E2E mechanism. When a E2E delay request is received on a port using the P2P mechanism. Syst em Administ rat ors Guide 286

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17.3. Using PTP with Multiple Interfaces When using PTP with multiple interfaces in different networks it is necessary to change the reverse path forwarding mode to loose mode. Red Hat Enterprise Linux 7 defaults to using Strict Reverse Path Forwarding following the Strict Reverse Path recommendation from RFC 3704 Ingress Filtering for Multihomed Networks. See the Reverse Path Forwarding section in the Red Hat Enterprise Linux 7 Security Guide for more details. The sysctl utility is used to read and write values to the kernel. Changes to a running system can be made using sysctl commands directly on the command line and permanent changes can be made by adding lines to the /etc/sysctl.conf file. To change to loose mode filtering globally enter the following commands as root: sysctl -w net.ipv4.conf.default.rp_filter2 sysctl -w net.ipv4.conf.all.rp_filter2 To change the reverse path filtering mode per network interface use the net.ipv4.interface.rp_filter command on all PTP interfaces. For example for an interface with device name em1: sysctl -w net.ipv4.conf.em1.rp_filter2 To make these settings persistent across reboots modify the /etc/sysctl.conf file. For example to change the mode for all interfaces open the /etc/sysctl.conf file with an editor running as the root user and add a line as follows: net.ipv4.conf.all.rp_filter2 To change only certain interfaces enter multiple lines in the following format: net.ipv4.conf.interface.rp_filter2 17.4. Specifying a Configuration File The command line options and other options which cannot be set on the command line can be set in an optional configuration file. No configuration file is read by default so it needs to be specified at runtime with the -f option. For example: ptp4l -f /etc/ptp4l.conf A configuration file equivalent to the -i eth3 -m -S options shown above would look as follows: cat /etc/ptp4l.conf global verbose 1 time_stamping software eth3 17.5. Using the PTP Management Client ⁠Chapt er 1 7 . Configuring PT P Using pt p4 l 287

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The PTP management client pmc can be used to obtain additional information from ptp4 l as follows: pmc -u -b 0 GET CURRENT_DATA_SET sending: GET CURRENT_DATA_SET 90e2ba.fffe.20c7f8-0 seq 0 RESPONSE MANAGMENT CURRENT_DATA_SET stepsRemoved 1 offsetFromMaster -142.0 meanPathDelay 9310.0 pmc -u -b 0 GET TIME_STATUS_NP sending: GET TIME_STATUS_NP 90e2ba.fffe.20c7f8-0 seq 0 RESPONSE MANAGMENT TIME_STATUS_NP master_offset 310 ingress_time 1361545089345029441 cumulativeScaledRateOffset +1.000000000 scaledLastGmPhaseChange 0 gmTimeBaseIndicator 0 lastGmPhaseChange 0x00000000000000000000.0000 gmPresent true gmIdentity 00a069.fffe.0b552d Setting the -b option to zero limits the boundary to the locally running ptp4 l instance. A larger boundary value will retrieve the information also from PTP nodes further from the local clock. The retrievable information includes: stepsRemoved is the number of communication paths to the grandmaster clock. offsetFromMaster and master_offset is the last measured offset of the clock from the master in nanoseconds. meanPathDelay is the estimated delay of the synchronization messages sent from the master in nanoseconds. if gmPresent is true the PTP clock is synchronized to a master the local clock is not the grandmaster clock. gmIdentity is the grandmasters identity. For a full list of pmc commands type the following as root: pmc help Additional information is available in the pmc8 man page. 17.6. Synchronizing the Clocks The phc2sys program is used to synchronize the system clock to the PTP hardware clock PHC on the NIC. The phc2sys service is configured in the /etc/sysconfig/phc2sys configuration file. The default setting in the /etc/sysconfig/phc2sys file is as follows: OPTIONS"-a -r" Syst em Administ rat ors Guide 288

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The -a option causes phc2sys to read the clocks to be synchronized from the ptp4 l application. It will follow changes in the PTP port states adjusting the synchronization between the NIC hardware clocks accordingly. The system clock is not synchronized unless the -r option is also specified. If you want the system clock to be eligible to become a time source specify the -r option twice. After making changes to /etc/sysconfig/phc2sys restart the phc2sys service from the command line by issuing a command as root: systemctl restart phc2sys Under normal circumstances use systemctl commands to start stop and restart the phc2sys service. When you do not want to start phc2sys as a service you can start it from the command line. For example enter the following command as root: phc2sys -a -r The -a option causes phc2sys to read the clocks to be synchronized from the ptp4 l application. If you want the system clock to be eligible to become a time source specify the -r option twice. Alternately use the -s option to synchronize the system clock to a specific interfaces PTP hardware clock. For example: phc2sys -s eth3 -w The -w option waits for the running ptp4 l application to synchronize the PTP clock and then retrieves the TAI to UTC offset from ptp4 l. Normally PTP operates in the International Atomic Time TAI timescale while the system clock is kept in Coordinated Universal Time UTC. The current offset between the TAI and UTC timescales is 36 seconds. The offset changes when leap seconds are inserted or deleted which typically happens every few years. The -O option needs to be used to set this offset manually when the -w is not used as follows: phc2sys -s eth3 -O -36 Once the phc2sys servo is in a locked state the clock will not be stepped unless the -S option is used. This means that the phc2sys program should be started after the ptp4 l program has synchronized the PTP hardware clock. However with -w it is not necessary to start phc2sys after ptp4 l as it will wait for it to synchronize the clock. The phc2sys program can also be started as a service by running: systemctl start phc2sys When running as a service options are specified in the /etc/sysconfig/phc2sys file. More information on the different phc2sys options can be found in the phc2sys8 man page. Note that the examples in this section assume the command is run on a slave system or slave port. 17.7. Verifying Time Synchronization ⁠Chapt er 1 7 . Configuring PT P Using pt p4 l 289

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When PTP time synchronization is working properly new messages with offsets and frequency adjustments will be printed periodically to the ptp4 l and phc2sys if hardware time stamping is used outputs. These values will eventually converge after a short period of time. These messages can be seen in /var/log/messages file. An example of the output follows: ptp4l352.359: selected /dev/ptp0 as PTP clock ptp4l352.361: port 1: INITIALIZING to LISTENING on INITIALIZE ptp4l352.361: port 0: INITIALIZING to LISTENING on INITIALIZE ptp4l353.210: port 1: new foreign master 00a069.fffe.0b552d-1 ptp4l357.214: selected best master clock 00a069.fffe.0b552d ptp4l357.214: port 1: LISTENING to UNCALIBRATED on RS_SLAVE ptp4l359.224: master offset 3304 s0 freq +0 path delay 9202 ptp4l360.224: master offset 3708 s1 freq -29492 path delay 9202 ptp4l361.224: master offset -3145 s2 freq -32637 path delay 9202 ptp4l361.224: port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED ptp4l362.223: master offset -145 s2 freq -30580 path delay 9202 ptp4l363.223: master offset 1043 s2 freq -29436 path delay 8972 ptp4l364.223: master offset 266 s2 freq -29900 path delay 9153 ptp4l365.223: master offset 430 s2 freq -29656 path delay 9153 ptp4l366.223: master offset 615 s2 freq -29342 path delay 9169 ptp4l367.222: master offset -191 s2 freq -29964 path delay 9169 ptp4l368.223: master offset 466 s2 freq -29364 path delay 9170 ptp4l369.235: master offset 24 s2 freq -29666 path delay 9196 ptp4l370.235: master offset -375 s2 freq -30058 path delay 9238 ptp4l371.235: master offset 285 s2 freq -29511 path delay 9199 ptp4l372.235: master offset -78 s2 freq -29788 path delay 9204 An example of the phc2sys output follows: phc2sys526.527: Waiting for ptp4l... phc2sys527.528: Waiting for ptp4l... phc2sys528.528: phc offset 55341 s0 freq +0 delay 2729 phc2sys529.528: phc offset 54658 s1 freq -37690 delay 2725 phc2sys530.528: phc offset 888 s2 freq -36802 delay 2756 phc2sys531.528: phc offset 1156 s2 freq -36268 delay 2766 phc2sys532.528: phc offset 411 s2 freq -36666 delay 2738 phc2sys533.528: phc offset -73 s2 freq -37026 delay 2764 phc2sys534.528: phc offset 39 s2 freq -36936 delay 2746 phc2sys535.529: phc offset 95 s2 freq -36869 delay 2733 phc2sys536.529: phc offset -359 s2 freq -37294 delay 2738 phc2sys537.529: phc offset -257 s2 freq -37300 delay 2753 phc2sys538.529: phc offset 119 s2 freq -37001 delay 2745 Syst em Administ rat ors Guide 290

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phc2sys539.529: phc offset 288 s2 freq -36796 delay 2766 phc2sys540.529: phc offset -149 s2 freq -37147 delay 2760 phc2sys541.529: phc offset -352 s2 freq -37395 delay 2771 phc2sys542.529: phc offset 166 s2 freq -36982 delay 2748 phc2sys543.529: phc offset 50 s2 freq -37048 delay 2756 phc2sys544.530: phc offset -31 s2 freq -37114 delay 2748 phc2sys545.530: phc offset -333 s2 freq -37426 delay 2747 phc2sys546.530: phc offset 194 s2 freq -36999 delay 2749 For ptp4 l there is also a directive summary_interval to reduce the output and print only statistics as normally it will print a message every second or so. For example to reduce the output to every 1024 seconds add the following line to the /etc/ptp4l.conf file: summary_interval 10 An example of the ptp4 l output with summary_interval 6 follows: ptp4l: 615.253 selected /dev/ptp0 as PTP clock ptp4l: 615.255 port 1: INITIALIZING to LISTENING on INITIALIZE ptp4l: 615.255 port 0: INITIALIZING to LISTENING on INITIALIZE ptp4l: 615.564 port 1: new foreign master 00a069.fffe.0b552d-1 ptp4l: 619.574 selected best master clock 00a069.fffe.0b552d ptp4l: 619.574 port 1: LISTENING to UNCALIBRATED on RS_SLAVE ptp4l: 623.573 port 1: UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED ptp4l: 684.649 rms 669 max 3691 freq -29383 ± 3735 delay 9232 ± 122 ptp4l: 748.724 rms 253 max 588 freq -29787 ± 221 delay 9219 ± 158 ptp4l: 812.793 rms 287 max 673 freq -29802 ± 248 delay 9211 ± 183 ptp4l: 876.853 rms 226 max 534 freq -29795 ± 197 delay 9221 ± 138 ptp4l: 940.925 rms 250 max 562 freq -29801 ± 218 delay 9199 ± 148 ptp4l: 1004.988 rms 226 max 525 freq -29802 ± 196 delay 9228 ± 143 ptp4l: 1069.065 rms 300 max 646 freq -29802 ± 259 delay 9214 ± 176 ptp4l: 1133.125 rms 226 max 505 freq -29792 ± 197 delay 9225 ± 159 ptp4l: 1197.185 rms 244 max 688 freq -29790 ± 211 delay 9201 ± 162 To reduce the output from the phc2sys it can be called it with the -u option as follows: phc2sys -u summary-updates Where summary-updates is the number of clock updates to include in summary statistics. An example follows: phc2sys -s eth3 -w -m -u 60 phc2sys700.948: rms 1837 max 10123 freq -36474 ± 4752 delay 2752 ± 16 phc2sys760.954: rms 194 max 457 freq -37084 ± 174 delay 2753 ± 12 phc2sys820.963: rms 211 max 487 freq -37085 ± 185 delay 2750 ± 19 phc2sys880.968: rms 183 max 440 freq -37102 ± 164 delay 2734 ± 91 phc2sys940.973: rms 244 max 584 freq -37095 ± 216 delay 2748 ± 16 phc2sys1000.979: rms 220 max 573 freq -36666 ± 182 delay 2747 ± 43 phc2sys1060.984: rms 266 max 675 freq -36759 ± 234 delay 2753 ± 17 17.8. Serving PTP Time with NTP ⁠Chapt er 1 7 . Configuring PT P Using pt p4 l 291

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The ntpd daemon can be configured to distribute the time from the system clock synchronized by ptp4 l or phc2sys by using the LOCAL reference clock driver. To prevent ntpd from adjusting the system clock the ntp.conf file must not specify any NTP servers. The following is a minimal example of ntp.conf: cat /etc/ntp.conf server 127.127.1.0 fudge 127.127.1.0 stratum 0 Note When the DHCP client program dhclient receives a list of NTP servers from the DHCP server it adds them to ntp.conf and restarts the service. To disable that feature add PEERNTPno to /etc/sysconfig/network. 17.9. Serving NTP Time with PTP NTP to PTP synchronization in the opposite direction is also possible. When ntpd is used to synchronize the system clock ptp4 l can be configured with the priority1 option or other clock options included in the best master clock algorithm to be the grandmaster clock and distribute the time from the system clock via PTP: cat /etc/ptp4l.conf global priority1 127 eth3 ptp4l -f /etc/ptp4l.conf With hardware time stamping phc2sys needs to be used to synchronize the PTP hardware clock to the system clock. If running phc2sys as a service edit the /etc/sysconfig/phc2sys configuration file. The default setting in the /etc/sysconfig/phc2sys file is as follows: OPTIONS"-a -r" As root edit that line as follows: vi /etc/sysconfig/phc2sys OPTIONS"-a -r -r" The -r option is used twice here to allow synchronization of the PTP hardware clock on the NIC from the system clock. Restart the phc2sys service for the changes to take effect: systemctl restart phc2sys To prevent quick changes in the PTP clocks frequency the synchronization to the system clock can be loosened by using smaller P proportional and I integral constants for the PI servo: phc2sys -a -r -r -P 0.01 -I 0.0001 17.10. Synchronize to PTP or NTP Time Using timemaster Syst em Administ rat ors Guide 292

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17.10. Synchronize to PTP or NTP Time Using timemaster When there are multiple PTP domains available on the network or fallback to NTP is needed the timemaster program can be used to synchronize the system clock to all available time sources. The PTP time is provided by phc2sys and ptp4 l via shared memory driver SHM reference clocks to chronyd or ntpd depending on the NTP daemon that has been configured on the system. The NTP daemon can then compare all time sources both PTP and NTP and use the best sources to synchronize the system clock. On start timemaster reads a configuration file that specifies the NTP and PTP time sources checks which network interfaces have their own or share a PTP hardware clock PHC generates configuration files for ptp4 l and chronyd or ntpd and starts the ptp4 l phc2sys and chronyd or ntpd processes as needed. It will remove the generated configuration files on exit. It writes configuration files for chronyd ntpd and ptp4 l to /var/run/timemaster/. 17.10.1. Starting timemaster as a Service To start timemaster as a service issue the following command as root: systemctl start timemaster This will read the options in /etc/timemaster.conf. For more information on managing system services in Red Hat Enterprise Linux 7 see Chapter 9 Managing Services with systemd. 17.10.2. Understanding the timemaster Configuration File Red Hat Enterprise Linux provides a default /etc/timemaster.conf file with a number of sections containing default options. The section headings are enclosed in brackets. To view the default configuration issue a command as follows: less /etc/timemaster.conf Configuration file for timemaster ntp_server ntp-server.local minpoll 4 maxpoll 4 ptp_domain 0 interfaces eth0 timemaster ntp_program chronyd chrony.conf include /etc/chrony.conf ntp.conf includefile /etc/ntp.conf ptp4l.conf chronyd path /usr/sbin/chronyd options -u chrony ⁠Chapt er 1 7 . Configuring PT P Using pt p4 l 293

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ntpd path /usr/sbin/ntpd options -u ntp:ntp -g phc2sys path /usr/sbin/phc2sys ptp4l path /usr/sbin/ptp4l Notice the section named as follows: ntp_server address This is an example of an NTP server section “ntp-server.local” is an example of a host name for an NTP server on the local LAN. Add more sections as required using a host name or IP address as part of the section name. Note that the short polling values in that example section are not suitable for a public server see Chapter 16 Configuring NTP Using ntpd for an explanation of suitable minpoll and maxpoll values. Notice the section named as follows: ptp_domain number A “PTP domain” is a group of one or more PTP clocks that synchronize to each other. They may or may not be synchronized to clocks in another domain. Clocks that are configured with the same domain number make up the domain. This includes a PTP grandmaster clock. The domain number in each “PTP domain” section needs to correspond to one of the PTP domains configured on the network. An instance of ptp4 l is started for every interface which has its own PTP clock and hardware time stamping is enabled automatically. Interfaces that support hardware time stamping have a PTP clock PHC attached however it is possible for a group of interfaces on a NIC to share a PHC. A separate ptp4 l instance will be started for each group of interfaces sharing the same PHC and for each interface that supports only software time stamping. All ptp4 l instances are configured to run as a slave. If an interface with hardware time stamping is specified in more than one PTP domain then only the first ptp4 l instance created will have hardware time stamping enabled. Notice the section named as follows: timemaster The default timemaster configuration includes the system ntpd and chrony configuration /etc/ntp.conf or /etc/chronyd.conf in order to include the configuration of access restrictions and authentication keys. That means any NTP servers specified there will be used with timemaster too. The section headings are as follows: ntp_server ntp-server.local — Specify polling intervals for this server. Create additional sections as required. Include the host name or IP address in the section heading. ptp_domain 0 — Specify interfaces that have PTP clocks configured for this domain. Create additional sections with the appropriate domain number as required. timemaster — Specify the NTP daemon to be used. Possible values are chronyd and ntpd. Syst em Administ rat ors Guide 294

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chrony.conf — Specify any additional settings to be copied to the configuration file generated for chronyd. ntp.conf — Specify any additional settings to be copied to the configuration file generated for ntpd. ptp4l.conf — Specify options to be copied to the configuration file generated for ptp4 l. chronyd — Specify any additional settings to be passed on the command line to chronyd. ntpd — Specify any additional settings to be passed on the command line to ntpd. phc2sys — Specify any additional settings to be passed on the command line to phc2sys. ptp4l — Specify any additional settings to be passed on the command line to all instances of ptp4 l. The section headings and there contents are explained in detail in the timemaster8 manual page. 17.10.3. Configuring timemaster Options Procedure 17.1. Editing the timemaster Configuration File 1. To change the default configuration open the /etc/timemaster.conf file for editing as root: vi /etc/timemaster.conf 2. For each NTP server you want to control using timemaster create ntp_server address sections . Note that the short polling values in the example section are not suitable for a public server see Chapter 16 Configuring NTP Using ntpd for an explanation of suitable minpoll and maxpoll values. 3. To add interfaces that should be used in a domain edit the ptp_domain 0 section and add the interfaces. Create additional domains as required. For example: ptp_domain 0 interfaces eth0 ptp_domain 1 interfaces eth1 4. If required to use ntpd as the NTP daemon on this system change the default entry in the timemaster section from chronyd to ntpd. See Chapter 15 Configuring NTP Using the chrony Suite for information on the differences between ntpd and chronyd. 5. If using chronyd as the NTP server on this system add any additional options below the default include /etc/chrony.conf entry in the chrony.conf section. Edit the default include entry if the path to /etc/chrony.conf is known to have changed. 6. If using ntpd as the NTP server on this system add any additional options below the default include /etc/ntp.conf entry in the ntp.conf section. Edit the default include entry if the path to /etc/ntp.conf is known to have changed. ⁠Chapt er 1 7 . Configuring PT P Using pt p4 l 295

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7. In the ptp4l.conf section add any options to be copied to the configuration file generated for ptp4 l. This chapter documents common options and more information is available in the ptp4l8 manual page. 8. In the chronyd section add any command line options to be passed to chronyd when called by timemaster. See Chapter 15 Configuring NTP Using the chrony Suite for information on using chronyd. 9. In the ntpd section add any command line options to be passed to ntpd when called by timemaster. See Chapter 16 Configuring NTP Using ntpd for information on using ntpd. 10. In the phc2sys section add any command line options to be passed to phc2sys when called by timemaster. This chapter documents common options and more information is available in the phy2sys8 manual page. 11. In the ptp4l section add any command line options to be passed to ptp4 l when called by timemaster. This chapter documents common options and more information is available in the ptp4l8 manual page. 12. Save the configuration file and restart timemaster by issuing the following command as root: systemctl restart timemaster 17.11. Improving Accuracy Previously test results indicated that disabling the tickless kernel capability could significantly improve the stability of the system clock and thus improve the PTP synchronization accuracy at the cost of increased power consumption. The kernel tickless mode can be disabled by adding nohzoff to the kernel boot option parameters. However recent improvements applied to kernel- 3.10.0-197.el7 have greatly improved the stability of the system clock and the difference in stability of the clock with and without nohzoff should be much smaller now for most users. The ptp4 l and phc2sys applications can be configured to use a new adaptive servo. The advantage over the PI servo is that it does not require configuration of the PI constants to perform well. To make use of this for ptp4 l add the following line to the /etc/ptp4l.conf file: clock_servo linreg After making changes to /etc/ptp4l.conf restart the ptp4 l service from the command line by issuing the following command as root: systemctl restart ptp4l To make use of this for phc2sys add the following line to the /etc/sysconfig/phc2sys file: -E linreg After making changes to /etc/sysconfig/phc2sys restart the phc2sys service from the command line by issuing the following command as root: systemctl restart phc2sys 17.12. Additional Resources Syst em Administ rat ors Guide 296

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17.12. Additional Resources The following sources of information provide additional resources regarding PTP and the ptp4 l tools. 17.12.1. Installed Documentation ptp4l8 man page — Describes ptp4 l options including the format of the configuration file. pmc8 man page — Describes the PTP management client and its command options. phc2sys8 man page — Describes a tool for synchronizing the system clock to a PTP hardware clock PHC. timemaster8 man page — Describes a program that uses ptp4 l and phc2sys to synchronize the system clock using chronyd or ntpd. 17.12.2. Useful Websites http://www.nist.gov/el/isd/ieee/ieee1588.cfm The IEEE 1588 Standard. ⁠Chapt er 1 7 . Configuring PT P Using pt p4 l 297

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⁠Part VI. Monitoring and Automation This part describes various tools that allow system administrators to monitor system performance automate system tasks and report bugs. Syst em Administ rat ors Guide 298

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Chapter 18. System Monitoring Tools In order to configure the system system administrators often need to determine the amount of free memory how much free disk space is available how the hard drive is partitioned or what processes are running. 18.1. Viewing System Processes 18.1.1. Using the ps Command The ps command allows you to display information about running processes. It produces a static list that is a snapshot of what is running when you execute the command. If you want a constantly updated list of running processes use the top command or the System Monitor application instead. To list all processes that are currently running on the system including processes owned by other users type the following at a shell prompt: ps ax For each listed process the ps ax command displays the process ID PID the terminal that is associated with it TTY the current status STAT the cumulated CPU time TIME and the name of the executable file COMMAND. For example: ps ax PID TTY STAT TIME COMMAND 1 Ss 0:01 /usr/lib/systemd/systemd --switched-root --system --deserialize 23 2 S 0:00 kthreadd 3 S 0:00 ksoftirqd/0 5 S 0:00 kworker/0:0H output truncated To display the owner alongside each process use the following command: ps aux Apart from the information provided by the ps ax command ps aux displays the effective user name of the process owner USER the percentage of the CPU CPU and memory MEM usage the virtual memory size in kilobytes VSZ the non-swapped physical memory size in kilobytes RSS and the time or date the process was started. For example: ps aux USER PID CPU MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.3 0.3 134776 6840 Ss 09:28 0:01 /usr/lib/systemd/systemd --switched-root --system --d root 2 0.0 0.0 0 0 S 09:28 0:00 kthreadd root 3 0.0 0.0 0 0 S 09:28 0:00 ksoftirqd/0 root 5 0.0 0.0 0 0 S 09:28 0:00 kworker/0:0H output truncated You can also use the ps command in a combination with grep to see if a particular process is running. For example to determine if Emacs is running type: ⁠Chapt er 1 8 . Syst em Monit oring T ools 299

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ps ax | grep emacs 12056 pts/3 S+ 0:00 emacs 12060 pts/2 S+ 0:00 grep --colorauto emacs For a complete list of available command line options see the ps1 manual page. 18.1.2. Using the top Command The top command displays a real-time list of processes that are running on the system. It also displays additional information about the system uptime current CPU and memory usage or total number of running processes and allows you to perform actions such as sorting the list or killing a process. To run the top command type the following at a shell prompt: top For each listed process the top command displays the process ID PID the effective user name of the process owner USER the priority PR the nice value NI the amount of virtual memory the process uses VIRT the amount of non-swapped physical memory the process uses RES the amount of shared memory the process uses SHR the process status field S the percentage of the CPU CPU and memory MEM usage the cumulated CPU time TIME+ and the name of the executable file COMMAND. For example: top top - 16:42:12 up 13 min 2 users load average: 0.67 0.31 0.19 Tasks: 165 total 2 running 163 sleeping 0 stopped 0 zombie Cpus: 37.5 us 3.0 sy 0.0 ni 59.5 id 0.0 wa 0.0 hi 0.0 si 0.0 st KiB Mem : 1016800 total 77368 free 728936 used 210496 buff/cache KiB Swap: 839676 total 776796 free 62880 used. 122628 avail Mem PID USER PR NI VIRT RES SHR S CPU MEM TIME+ COMMAND 3168 sjw 20 0 1454628 143240 15016 S 20.3 14.1 0:22.53 gnome- shell 4006 sjw 20 0 1367832 298876 27856 S 13.0 29.4 0:15.58 firefox 1683 root 20 0 242204 50464 4268 S 6.0 5.0 0:07.76 Xorg 4125 sjw 20 0 555148 19820 12644 S 1.3 1.9 0:00.48 gnome- terminal- 10 root 20 0 0 0 0 S 0.3 0.0 0:00.39 rcu_sched 3091 sjw 20 0 37000 1468 904 S 0.3 0.1 0:00.31 dbus- daemon 3096 sjw 20 0 129688 2164 1492 S 0.3 0.2 0:00.14 at- spi2-registr 3925 root 20 0 0 0 0 S 0.3 0.0 0:00.05 kworker/0:0 1 root 20 0 126568 3884 1052 S 0.0 0.4 0:01.61 systemd 2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd Syst em Administ rat ors Guide 300

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3 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0 6 root 20 0 0 0 0 S 0.0 0.0 0:00.07 kworker/u2:0 output truncated Table 18.1 “Interactive top commands” contains useful interactive commands that you can use with top. For more information see the top1 manual page. Table 18.1. Interactive top commands Command Description Enter Space Immediately refreshes the display. h Displays a help screen for interactive commands. h Displays a help screen for windows and field groups. k Kills a process. You are prompted for the process ID and the signal to send to it. n Changes the number of displayed processes. You are prompted to enter the number. u Sorts the list by user. M Sorts the list by memory usage. P Sorts the list by CPU usage. q Terminates the utility and returns to the shell prompt. 18.1.3. Using the System Monitor T ool The Processes tab of the System Monitor tool allows you to view search for change the priority of and kill processes from the graphical user interface. To start the System Monitor tool from the command line type gnome-system-monitor at a shell prompt. The System Monitor tool appears. Alternatively if using the GNOME desktop press the Super key to enter the Activities Overview type System Monitor and then press Enter. The System Monitor tool appears. The Super key appears in a variety of guises depending on the keyboard and other hardware but often as either the Windows or Command key and typically to the left of the Spacebar. Click the Processes tab to view the list of running processes. ⁠Chapt er 1 8 . Syst em Monit oring T ools 301

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Figure 18.1. System Monitor — Processes For each listed process the System Monitor tool displays its name Process Name current status Status percentage of the CPU usage CPU nice value Nice process ID ID memory usage Memory the channel the process is waiting in Waiting Channel and additional details about the session Session. To sort the information by a specific column in ascending order click the name of that column. Click the name of the column again to toggle the sort between ascending and descending order. By default the System Monitor tool displays a list of processes that are owned by the current user. Selecting various options from the View menu allows you to: view only active processes view all processes view your processes view process dependencies Additionally two buttons enable you to: refresh the list of processes end a process by selecting it from the list and then clicking the End Process button. 18.2. Viewing Memory Usage 18.2.1. Using the free Command The free command allows you to display the amount of free and used memory on the system. To do so type the following at a shell prompt: free Syst em Administ rat ors Guide 302

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The free command provides information about both the physical memory Mem and swap space Swap. It displays the total amount of memory total as well as the amount of memory that is in use used free free shared shared sum of buffers and cached buff/cache and available available. For example: free total used free shared buff/cache available Mem: 1016800 727300 84684 3500 204816 124068 Swap: 839676 66920 772756 By default free displays the values in kilobytes. To display the values in megabytes supply the -m command line option: free -m For instance: free -m total used free shared buff/cache available Mem: 992 711 81 3 200 120 Swap: 819 65 754 For a complete list of available command line options see the free1 manual page. 18.2.2. Using the System Monitor T ool The Resources tab of the System Monitor tool allows you to view the amount of free and used memory on the system. To start the System Monitor tool from the command line type gnome-system-monitor at a shell prompt. The System Monitor tool appears. Alternatively if using the GNOME desktop press the Super key to enter the Activities Overview type System Monitor and then press Enter. The System Monitor tool appears. The Super key appears in a variety of guises depending on the keyboard and other hardware but often as either the Windows or Command key and typically to the left of the Spacebar. Click the Resources tab to view the systems memory usage. ⁠Chapt er 1 8 . Syst em Monit oring T ools 303

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Figure 18.2. System Monitor — Resources In the Memory and Swap History section the System Monitor tool displays a graphical representation of the memory and swap usage history as well as the total amount of the physical memory Memory and swap space Swap and how much of it is in use. 18.3. Viewing CPU Usage 18.3.1. Using the System Monitor T ool The Resources tab of the System Monitor tool allows you to view the current CPU usage on the system. To start the System Monitor tool from the command line type gnome-system-monitor at a shell prompt. The System Monitor tool appears. Alternatively if using the GNOME desktop press the Super key to enter the Activities Overview type System Monitor and then press Enter. The System Monitor tool appears. The Super key appears in a variety of guises depending on the keyboard and other hardware but often as either the Windows or Command key and typically to the left of the Spacebar. Click the Resources tab to view the systems CPU usage. In the CPU History section the System Monitor tool displays a graphical representation of the CPU usage history and shows the percentage of how much CPU is currently in use. 18.4. Viewing Block Devices and File Systems 18.4 .1. Using the lsblk Command Syst em Administ rat ors Guide 304

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The lsblk command allows you to display a list of available block devices. It provides more information and better control on output formatting than the blkid command. It reads information from udev therefore it is usable by non-root users. To display a list of block devices type the following at a shell prompt: lsblk For each listed block device the lsblk command displays the device name NAME major and minor device number MAJ:MIN if the device is removable RM its size SIZE if the device is read- only RO what type it is TYPE and where the device is mounted MOUNTPOINT. For example: lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sr0 11:0 1 1024M 0 rom vda 252:0 0 20G 0 rom |-vda1 252:1 0 500M 0 part /boot `-vda2 252:2 0 19.5G 0 part |-vg_kvm-lv_root dm-0 253:0 0 18G 0 lvm / `-vg_kvm-lv_swap dm-1 253:1 0 1.5G 0 lvm SWAP By default lsblk lists block devices in a tree-like format. To display the information as an ordinary list add the -l command line option: lsblk -l For instance: lsblk -l NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sr0 11:0 1 1024M 0 rom vda 252:0 0 20G 0 rom vda1 252:1 0 500M 0 part /boot vda2 252:2 0 19.5G 0 part vg_kvm-lv_root dm-0 253:0 0 18G 0 lvm / vg_kvm-lv_swap dm-1 253:1 0 1.5G 0 lvm SWAP For a complete list of available command line options see the lsblk8 manual page. 18.4 .2. Using the blkid Command The blkid command allows you to display low-level information about available block devices. It requires root privileges therefore non-root users should use the lsblk command. To do so type the following at a shell prompt as root: blkid For each listed block device the blkid command displays available attributes such as its universally unique identifier UUID file system type TYPE or volume label LABEL. For example: blkid /dev/vda1: UUID"7fa9c421-0054-4555-b0ca-b470a97a3d84" TYPE"ext4" /dev/vda2: UUID"7IvYzk-TnnK-oPjf-ipdD-cofz-DXaJ-gPdgBW" TYPE"LVM2_member" ⁠Chapt er 1 8 . Syst em Monit oring T ools 305

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/dev/mapper/vg_kvm-lv_root: UUID"a07b967c-71a0-4925-ab02-aebcad2ae824" TYPE"ext4" /dev/mapper/vg_kvm-lv_swap: UUID"d7ef54ca-9c41-4de4-ac1b-4193b0c1ddb6" TYPE"swap" By default the blkid command lists all available block devices. To display information about a particular device only specify the device name on the command line: blkid device_name For instance to display information about /dev/vda1 type as root: blkid /dev/vda1 /dev/vda1: UUID"7fa9c421-0054-4555-b0ca-b470a97a3d84" TYPE"ext4" You can also use the above command with the -p and -o udev command line options to obtain more detailed information. Note that root privileges are required to run this command: blkid -po udev device_name For example: blkid -po udev /dev/vda1 ID_FS_UUID7fa9c421-0054-4555-b0ca-b470a97a3d84 ID_FS_UUID_ENC7fa9c421-0054-4555-b0ca-b470a97a3d84 ID_FS_VERSION1.0 ID_FS_TYPEext4 ID_FS_USAGEfilesystem For a complete list of available command line options see the blkid8 manual page. 18.4 .3. Using the findmnt Command The findmnt command allows you to display a list of currently mounted file systems. To do so type the following at a shell prompt: findmnt For each listed file system the findmnt command displays the target mount point TARGET source device SOURCE file system type FSTYPE and relevant mount options OPTIONS. For example: findmnt TARGET SOURCE FSTYPE OPTIONS / /dev/mapper/rhel-root xfs rwrelatimeseclabelattr2inode64noquota ├─/proc proc proc rwnosuidnodevnoexecrelatime │ ├─/proc/sys/fs/binfmt_misc systemd-1 autofs rwrelatimefd32pgrp1timeout300minproto5maxproto5direct │ └─/proc/fs/nfsd sunrpc nfsd rwrelatime Syst em Administ rat ors Guide 306

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├─/sys sysfs sysfs rwnosuidnodevnoexecrelatimeseclabel │ ├─/sys/kernel/security securityfs securityfs rwnosuidnodevnoexecrelatime │ ├─/sys/fs/cgroup tmpfs tmpfs rwnosuidnodevnoexecseclabelmode755 output truncated By default findmnt lists file systems in a tree-like format. To display the information as an ordinary list add the -l command line option: findmnt -l For instance: findmnt -l TARGET SOURCE FSTYPE OPTIONS /proc proc proc rwnosuidnodevnoexecrelatime /sys sysfs sysfs rwnosuidnodevnoexecrelatimeseclabel /dev devtmpfs devtmpfs rwnosuidseclabelsize933372knr_inodes233343mode755 /sys/kernel/security securityfs securityfs rwnosuidnodevnoexecrelatime /dev/shm tmpfs tmpfs rwnosuidnodevseclabel /dev/pts devpts devpts rwnosuidnoexecrelatimeseclabelgid5mode620ptmxmode000 /run tmpfs tmpfs rwnosuidnodevseclabelmode755 /sys/fs/cgroup tmpfs tmpfs rwnosuidnodevnoexecseclabelmode755 output truncated You can also choose to list only file systems of a particular type. To do so add the -t command line option followed by a file system type: findmnt -t type For example to all list xfs file systems type: findmnt -t xfs TARGET SOURCE FSTYPE OPTIONS / /dev/mapper/rhel-root xfs rwrelatimeseclabelattr2inode64noquota └─/boot /dev/vda1 xfs rwrelatimeseclabelattr2inode64noquota For a complete list of available command line options see the findmnt8 manual page. 18.4 .4 . Using the df Command ⁠Chapt er 1 8 . Syst em Monit oring T ools 307

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The df command allows you to display a detailed report on the systems disk space usage. To do so type the following at a shell prompt: df For each listed file system the df command displays its name Filesystem size 1K-blocks or Size how much space is used Used how much space is still available Available the percentage of space usage Use and where is the file system mounted Mounted on. For example: df Filesystem 1K-blocks Used Available Use Mounted on /dev/mapper/vg_kvm-lv_root 18618236 4357360 13315112 25 / tmpfs 380376 288 380088 1 /dev/shm /dev/vda1 495844 77029 393215 17 /boot By default the df command shows the partition size in 1 kilobyte blocks and the amount of used and available disk space in kilobytes. To view the information in megabytes and gigabytes supply the -h command line option which causes df to display the values in a human-readable format: df -h For instance: df -h Filesystem Size Used Avail Use Mounted on /dev/mapper/vg_kvm-lv_root 18G 4.2G 13G 25 / tmpfs 372M 288K 372M 1 /dev/shm /dev/vda1 485M 76M 384M 17 /boot For a complete list of available command line options see the df1 manual page. 18.4 .5. Using the du Command The du command allows you to displays the amount of space that is being used by files in a directory. To display the disk usage for each of the subdirectories in the current working directory run the command with no additional command line options: du For example: du 14972 ./Downloads 4 ./.mozilla/extensions 4 ./.mozilla/plugins 12 ./.mozilla 15004 . By default the du command displays the disk usage in kilobytes. To view the information in megabytes and gigabytes supply the -h command line option which causes the utility to display the values in a human-readable format: Syst em Administ rat ors Guide 308

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du -h For instance: du -h 15M ./Downloads 4.0K ./.mozilla/extensions 4.0K ./.mozilla/plugins 12K ./.mozilla 15M . At the end of the list the du command always shows the grand total for the current directory. To display only this information supply the -s command line option: du -sh For example: du -sh 15M . For a complete list of available command line options see the du1 manual page. 18.4 .6. Using the System Monitor T ool The File Systems tab of the System Monitor tool allows you to view file systems and disk space usage in the graphical user interface. To start the System Monitor tool from the command line type gnome-system-monitor at a shell prompt. The System Monitor tool appears. Alternatively if using the GNOME desktop press the Super key to enter the Activities Overview type System Monitor and then press Enter. The System Monitor tool appears. The Super key appears in a variety of guises depending on the keyboard and other hardware but often as either the Windows or Command key and typically to the left of the Spacebar. Click the File Systems tab to view a list of file systems. Figure 18.3. System Monitor — File Systems ⁠Chapt er 1 8 . Syst em Monit oring T ools 309

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For each listed file system the System Monitor tool displays the source device Device target mount point Directory and file system type Type as well as its size Total and how much space is available Available and used Used. 18.5. Viewing Hardware Information 18.5.1. Using the lspci Command The lspci command allows you to display information about PCI buses and devices that are attached to them. To list all PCI devices that are in the system type the following at a shell prompt: lspci This displays a simple list of devices for example: lspci 00:00.0 Host bridge: Intel Corporation 82X38/X48 Express DRAM Controller 00:01.0 PCI bridge: Intel Corporation 82X38/X48 Express Host-Primary PCI Express Bridge 00:1a.0 USB Controller: Intel Corporation 82801I ICH9 Family USB UHCI Controller 4 rev 02 00:1a.1 USB Controller: Intel Corporation 82801I ICH9 Family USB UHCI Controller 5 rev 02 00:1a.2 USB Controller: Intel Corporation 82801I ICH9 Family USB UHCI Controller 6 rev 02 output truncated You can also use the -v command line option to display more verbose output or -vv for very verbose output: lspci -v|-vv For instance to determine the manufacturer model and memory size of a systems video card type: lspci -v output truncated 01:00.0 VGA compatible controller: nVidia Corporation G84 Quadro FX 370 rev a1 prog-if 00 VGA controller Subsystem: nVidia Corporation Device 0491 Physical Slot: 2 Flags: bus master fast devsel latency 0 IRQ 16 Memory at f2000000 32-bit non-prefetchable size16M Memory at e0000000 64-bit prefetchable size256M Memory at f0000000 64-bit non-prefetchable size32M I/O ports at 1100 size128 Expansion ROM at unassigned disabled Capabilities: access denied Kernel driver in use: nouveau Kernel modules: nouveau nvidiafb output truncated Syst em Administ rat ors Guide 310

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For a complete list of available command line options see the lspci8 manual page. 18.5.2. Using the lsusb Command The lsusb command allows you to display information about USB buses and devices that are attached to them. To list all USB devices that are in the system type the following at a shell prompt: lsusb This displays a simple list of devices for example: lsusb Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub output truncated Bus 001 Device 002: ID 0bda:0151 Realtek Semiconductor Corp. Mass Storage Device Multicard Reader Bus 008 Device 002: ID 03f0:2c24 Hewlett-Packard Logitech M-UAL-96 Mouse Bus 008 Device 003: ID 04b3:3025 IBM Corp. You can also use the -v command line option to display more verbose output: lsusb -v For instance: lsusb -v output truncated Bus 008 Device 002: ID 03f0:2c24 Hewlett-Packard Logitech M-UAL-96 Mouse Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 2.00 bDeviceClass 0 Defined at Interface level bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 8 idVendor 0x03f0 Hewlett-Packard idProduct 0x2c24 Logitech M-UAL-96 Mouse bcdDevice 31.00 iManufacturer 1 iProduct 2 iSerial 0 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 output truncated For a complete list of available command line options see the lsusb8 manual page. 18.5.3. Using the lscpu Command ⁠Chapt er 1 8 . Syst em Monit oring T ools 311

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The lscpu command allows you to list information about CPUs that are present in the system including the number of CPUs their architecture vendor family model CPU caches etc. To do so type the following at a shell prompt: lscpu For example: lscpu Architecture: x86_64 CPU op-modes: 32-bit 64-bit Byte Order: Little Endian CPUs: 4 On-line CPUs list: 0-3 Threads per core: 1 Cores per socket: 4 Sockets: 1 NUMA nodes: 1 Vendor ID: GenuineIntel CPU family: 6 Model: 23 Stepping: 7 CPU MHz: 1998.000 BogoMIPS: 4999.98 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 3072K NUMA node0 CPUs: 0-3 For a complete list of available command line options see the lscpu1 manual page. 18.6. Checking for Hardware Errors Red Hat Enterprise Linux 7 introduced the new hardware event report mechanism HERM. This mechanism gathers system-reported memory errors as well as errors reported by the error detection and correction EDAC mechanism for dual in-line memory modules DIMMs and reports them to user space. The user-space daemon rasdaemon catches and handles all reliability availability and serviceability RAS error events that come from the kernel tracing mechanism and logs them. The functions previously provided by edac-utils are now replaced by rasdaemon. To install rasdaemon enter the following command as root: yum install rasdaemon Start the service as follows: systemctl start rasdaemon To make the service run at system start enter the following command: systemctl enable rasdaemon Syst em Administ rat ors Guide 312

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The ras-mc-ctl utility provides a means to work with EDAC drivers. Enter the following command to see a list of command options: ras-mc-ctl --help Usage: ras-mc-ctl OPTIONS... --quiet Quiet operation. --mainboard Print mainboard vendor and model for this hardware. --status Print status of EDAC drivers. output truncated To view a summary of memory controller events run as root: ras-mc-ctl --summary Memory controller events summary: Corrected on DIMM Labels: CPU_SrcID0_Ha0_Chan0_DIMM0 location: 0:0:0:-1 errors: 1 No PCIe AER errors. No Extlog errors. MCE records summary: 1 MEMORY CONTROLLER RD_CHANNEL0_ERR Transaction: Memory read error errors 2 No Error errors To view a list of errors reported by the memory controller run as root: ras-mc-ctl --errors Memory controller events: 1 3172-02-17 00:47:01 -0500 1 Corrected errors: memory read error at CPU_SrcID0_Ha0_Chan0_DIMM0 location: 0:0:0:-1 addr 65928 grain 7 syndrome 0 area:DRAM err_code:0001:0090 socket:0 ha:0 channel_mask:1 rank:0 No PCIe AER errors. No Extlog errors. MCE events: 1 3171-11-09 06:20:21 -0500 error: MEMORY CONTROLLER RD_CHANNEL0_ERR Transaction: Memory read error mcg mcgstatus0 mci Corrected_error n_errors1 mcgcap0x01000c16 status0x8c00004000010090 addr0x1018893000 misc0x15020a086 walltime0x57e96780 cpuid0x00050663 bank0x00000007 2 3205-06-22 00:13:41 -0400 error: No Error mcg mcgstatus0 mci Corrected_error Error_enabled mcgcap0x01000c16 status0x9400000000000000 addr0x0000abcd walltime0x57e967ea cpuid0x00050663 bank0x00000001 3 3205-06-22 00:13:41 -0400 error: No Error mcg mcgstatus0 mci Corrected_error Error_enabled mcgcap0x01000c16 status0x9400000000000000 addr0x00001234 walltime0x57e967ea cpu0x00000001 cpuid0x00050663 apicid0x00000002 bank0x00000002 These commands are also described in the ras-mc-ctl8 manual page. ⁠Chapt er 1 8 . Syst em Monit oring T ools 313

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18.7. Monitoring Performance with Net-SNMP Red Hat Enterprise Linux 7 includes the Net-SNMP software suite which includes a flexible and extensible simple network management protocol SNMP agent. This agent and its associated utilities can be used to provide performance data from a large number of systems to a variety of tools which support polling over the SNMP protocol. This section provides information on configuring the Net-SNMP agent to securely provide performance data over the network retrieving the data using the SNMP protocol and extending the SNMP agent to provide custom performance metrics. 18.7.1. Installing Net-SNMP The Net-SNMP software suite is available as a set of RPM packages in the Red Hat Enterprise Linux software distribution. Table 18.2 “Available Net-SNMP packages” summarizes each of the packages and their contents. Table 18.2. Available Net-SNMP packages Package Provides net-snmp The SNMP Agent Daemon and documentation. This package is required for exporting performance data. net-snmp-libs The netsnmp library and the bundled management information bases MIBs. This package is required for exporting performance data. net-snmp-utils SNMP clients such as snmpget and snmpwalk. This package is required in order to query a systems performance data over SNMP. net-snmp-perl The mib2c utility and the NetSNMP Perl module. Note that this package is provided by the Optional channel. See Section 8.5.7 “Adding the Optional and Supplementary Repositories” for more information on Red Hat additional channels. net-snmp-python An SNMP client library for Python. Note that this package is provided by the Optional channel. See Section 8.5.7 “Adding the Optional and Supplementary Repositories” for more information on Red Hat additional channels. To install any of these packages use the yum command in the following form: yum install package… For example to install the SNMP Agent Daemon and SNMP clients used in the rest of this section type the following at a shell prompt as root: yum install net-snmp net-snmp-libs net-snmp-utils For more information on how to install new packages in Red Hat Enterprise Linux see Section 8.2.4 “Installing Packages”. 18.7.2. Running the Net-SNMP Daemon The net-snmp package contains snmpd the SNMP Agent Daemon. This section provides information on how to start stop and restart the snmpd service. For more information on managing system services in Red Hat Enterprise Linux 7 see Chapter 9 Managing Services with systemd. Syst em Administ rat ors Guide 314

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18.7.2.1. St art ing t he Service To run the snmpd service in the current session type the following at a shell prompt as root: systemctl start snmpd.service To configure the service to be automatically started at boot time use the following command: systemctl enable snmpd.service 18.7.2.2. St o pping t he Service To stop the running snmpd service type the following at a shell prompt as root: systemctl stop snmpd.service To disable starting the service at boot time use the following command: systemctl disable snmpd.service 18.7.2.3. Rest art ing t he Service To restart the running snmpd service type the following at a shell prompt: systemctl restart snmpd.service This command stops the service and starts it again in quick succession. To only reload the configuration without stopping the service run the following command instead: systemctl reload snmpd.service This causes the running snmpd service to reload its configuration. 18.7.3. Configuring Net-SNMP To change the Net-SNMP Agent Daemon configuration edit the /etc/snmp/snmpd.conf configuration file. The default snmpd.conf file included with Red Hat Enterprise Linux 7 is heavily commented and serves as a good starting point for agent configuration. This section focuses on two common tasks: setting system information and configuring authentication. For more information about available configuration directives see the snmpd.conf5 manual page. Additionally there is a utility in the net-snmp package named snmpconf which can be used to interactively generate a valid agent configuration. Note that the net-snmp-utils package must be installed in order to use the snmpwalk utility described in this section. ⁠Chapt er 1 8 . Syst em Monit oring T ools 315

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Note For any changes to the configuration file to take effect force the snmpd service to re-read the configuration by running the following command as root: systemctl reload snmpd.service 18.7.3.1. Set t ing Syst em Info rmat io n Net-SNMP provides some rudimentary system information via the system tree. For example the following snmpwalk command shows the system tree with a default agent configuration. snmpwalk -v2c -c public localhost system SNMPv2-MIB::sysDescr.0 STRING: Linux localhost.localdomain 3.10.0- 123.el7.x86_64 1 SMP Mon May 5 11:16:57 EDT 2014 x86_64 SNMPv2-MIB::sysObjectID.0 OID: NET-SNMP-MIB::netSnmpAgentOIDs.10 DISMAN-EVENT-MIB::sysUpTimeInstance Timeticks: 464 0:00:04.64 SNMPv2-MIB::sysContact.0 STRING: Root rootlocalhost configure /etc/snmp/snmp.local.conf output truncated By default the sysName object is set to the host name. The sysLocation and sysContact objects can be configured in the /etc/snmp/snmpd.conf file by changing the value of the syslocation and syscontact directives for example: syslocation Datacenter Row 4 Rack 3 syscontact UNIX Admin adminexample.com After making changes to the configuration file reload the configuration and test it by running the snmpwalk command again: systemctl reload snmp.service snmpwalk -v2c -c public localhost system SNMPv2-MIB::sysDescr.0 STRING: Linux localhost.localdomain 3.10.0- 123.el7.x86_64 1 SMP Mon May 5 11:16:57 EDT 2014 x86_64 SNMPv2-MIB::sysObjectID.0 OID: NET-SNMP-MIB::netSnmpAgentOIDs.10 DISMAN-EVENT-MIB::sysUpTimeInstance Timeticks: 35424 0:05:54.24 SNMPv2-MIB::sysContact.0 STRING: UNIX Admin adminexample.com SNMPv2-MIB::sysName.0 STRING: localhost.localdomain SNMPv2-MIB::sysLocation.0 STRING: Datacenter Row 4 Rack 3 output truncated 18.7.3.2. Co nfiguring Aut hent icat io n The Net-SNMP Agent Daemon supports all three versions of the SNMP protocol. The first two versions 1 and 2c provide for simple authentication using a community string. This string is a shared secret between the agent and any client utilities. The string is passed in clear text over the network however and is not considered secure. Version 3 of the SNMP protocol supports user authentication and message encryption using a variety of protocols. The Net-SNMP agent also supports tunneling over SSH TLS authentication with X.509 certificates and Kerberos authentication. Syst em Administ rat ors Guide 316

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Configuring SNMP Version 2c Community To configure an SNMP version 2c community use either the rocommunity or rwcommunity directive in the /etc/snmp/snmpd.conf configuration file. The format of the directives is as follows: directive community source OID … where community is the community string to use source is an IP address or subnet and OID is the SNMP tree to provide access to. For example the following directive provides read-only access to the system tree to a client using the community string “redhat” on the local machine: rocommunity redhat 127.0.0.1 .1.3.6.1.2.1.1 To test the configuration use the snmpwalk command with the -v and -c options. snmpwalk -v2c -c redhat localhost system SNMPv2-MIB::sysDescr.0 STRING: Linux localhost.localdomain 3.10.0- 123.el7.x86_64 1 SMP Mon May 5 11:16:57 EDT 2014 x86_64 SNMPv2-MIB::sysObjectID.0 OID: NET-SNMP-MIB::netSnmpAgentOIDs.10 DISMAN-EVENT-MIB::sysUpTimeInstance Timeticks: 101376 0:16:53.76 SNMPv2-MIB::sysContact.0 STRING: UNIX Admin adminexample.com SNMPv2-MIB::sysName.0 STRING: localhost.localdomain SNMPv2-MIB::sysLocation.0 STRING: Datacenter Row 4 Rack 3 output truncated Configuring SNMP Version 3 User To configure an SNMP version 3 user use the net-snmp-create-v3-user command. This command adds entries to the /var/lib/net-snmp/snmpd.conf and /etc/snmp/snmpd.conf files which create the user and grant access to the user. Note that the net-snmp-create-v3-user command may only be run when the agent is not running. The following example creates the “admin” user with the password “redhatsnmp”: systemctl stop snmpd.service net-snmp-create-v3-user Enter a SNMPv3 user name to create: admin Enter authentication pass-phrase: redhatsnmp Enter encryption pass-phrase: press return to reuse the authentication pass-phrase adding the following line to /var/lib/net-snmp/snmpd.conf: createUser admin MD5 "redhatsnmp" DES adding the following line to /etc/snmp/snmpd.conf: rwuser admin systemctl start snmpd.service The rwuser directive or rouser when the -ro command line option is supplied that net-snmp- create-v3-user adds to /etc/snmp/snmpd.conf has a similar format to the rwcommunity and rocommunity directives: directive user noauth|auth|priv OID ⁠Chapt er 1 8 . Syst em Monit oring T ools 317

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… where user is a user name and OID is the SNMP tree to provide access to. By default the Net- SNMP Agent Daemon allows only authenticated requests the auth option. The noauth option allows you to permit unauthenticated requests and the priv option enforces the use of encryption. The authpriv option specifies that requests must be authenticated and replies should be encrypted. For example the following line grants the user “admin” read-write access to the entire tree: rwuser admin authpriv .1 To test the configuration create a .snmp/ directory in your users home directory and a configuration file named snmp.conf in that directory /.snmp/snmp.conf with the following lines: defVersion 3 defSecurityLevel authPriv defSecurityName admin defPassphrase redhatsnmp The snmpwalk command will now use these authentication settings when querying the agent: snmpwalk -v3 localhost system SNMPv2-MIB::sysDescr.0 STRING: Linux localhost.localdomain 3.10.0- 123.el7.x86_64 1 SMP Mon May 5 11:16:57 EDT 2014 x86_64 output truncated 18.7.4 . Retrieving Performance Data over SNMP The Net-SNMP Agent in Red Hat Enterprise Linux provides a wide variety of performance information over the SNMP protocol. In addition the agent can be queried for a listing of the installed RPM packages on the system a listing of currently running processes on the system or the network configuration of the system. This section provides an overview of OIDs related to performance tuning available over SNMP. It assumes that the net-snmp-utils package is installed and that the user is granted access to the SNMP tree as described in Section 18.7.3.2 “Configuring Authentication”. 18.7.4.1. Hardware Co nfigurat io n The Host Resources MIB included with Net-SNMP presents information about the current hardware and software configuration of a host to a client utility. Table 18.3 “Available OIDs” summarizes the different OIDs available under that MIB. Table 18.3. Available OIDs OID Description HOST-RESOURCES-MIB::hrSystem Contains general system information such as uptime number of users and number of running processes. HOST-RESOURCES-MIB::hrStorage Contains data on memory and file system usage. HOST-RESOURCES-MIB::hrDevices Contains a listing of all processors network devices and file systems. HOST-RESOURCES-MIB::hrSWRun Contains a listing of all running processes. Syst em Administ rat ors Guide 318

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HOST-RESOURCES-MIB::hrSWRunPerf Contains memory and CPU statistics on the process table from HOST-RESOURCES- MIB::hrSWRun. HOST-RESOURCES-MIB::hrSWInstalled Contains a listing of the RPM database. OID Description There are also a number of SNMP tables available in the Host Resources MIB which can be used to retrieve a summary of the available information. The following example displays HOST- RESOURCES-MIB::hrFSTable: snmptable -Cb localhost HOST-RESOURCES-MIB::hrFSTable SNMP table: HOST-RESOURCES-MIB::hrFSTable Index MountPoint RemoteMountPoint Type Access Bootable StorageIndex LastFullBackupDate LastPartialBackupDate 1 "/" "" HOST-RESOURCES-TYPES::hrFSLinuxExt2 readWrite true 31 0-1-10:0:0.0 0-1-10:0:0.0 5 "/dev/shm" "" HOST-RESOURCES-TYPES::hrFSOther readWrite false 35 0-1-10:0:0.0 0-1-10:0:0.0 6 "/boot" "" HOST-RESOURCES-TYPES::hrFSLinuxExt2 readWrite false 36 0-1-10:0:0.0 0-1-10:0:0.0 For more information about HOST-RESOURCES-MIB see the /usr/share/snmp/mibs/HOST- RESOURCES-MIB.txt file. 18.7.4.2. CPU and Memo ry Info rmat io n Most system performance data is available in the UCD SNMP MIB. The systemStats OID provides a number of counters around processor usage: snmpwalk localhost UCD-SNMP-MIB::systemStats UCD-SNMP-MIB::ssIndex.0 INTEGER: 1 UCD-SNMP-MIB::ssErrorName.0 STRING: systemStats UCD-SNMP-MIB::ssSwapIn.0 INTEGER: 0 kB UCD-SNMP-MIB::ssSwapOut.0 INTEGER: 0 kB UCD-SNMP-MIB::ssIOSent.0 INTEGER: 0 blocks/s UCD-SNMP-MIB::ssIOReceive.0 INTEGER: 0 blocks/s UCD-SNMP-MIB::ssSysInterrupts.0 INTEGER: 29 interrupts/s UCD-SNMP-MIB::ssSysContext.0 INTEGER: 18 switches/s UCD-SNMP-MIB::ssCpuUser.0 INTEGER: 0 UCD-SNMP-MIB::ssCpuSystem.0 INTEGER: 0 UCD-SNMP-MIB::ssCpuIdle.0 INTEGER: 99 UCD-SNMP-MIB::ssCpuRawUser.0 Counter32: 2278 UCD-SNMP-MIB::ssCpuRawNice.0 Counter32: 1395 UCD-SNMP-MIB::ssCpuRawSystem.0 Counter32: 6826 UCD-SNMP-MIB::ssCpuRawIdle.0 Counter32: 3383736 UCD-SNMP-MIB::ssCpuRawWait.0 Counter32: 7629 UCD-SNMP-MIB::ssCpuRawKernel.0 Counter32: 0 UCD-SNMP-MIB::ssCpuRawInterrupt.0 Counter32: 434 UCD-SNMP-MIB::ssIORawSent.0 Counter32: 266770 UCD-SNMP-MIB::ssIORawReceived.0 Counter32: 427302 UCD-SNMP-MIB::ssRawInterrupts.0 Counter32: 743442 ⁠Chapt er 1 8 . Syst em Monit oring T ools 319

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UCD-SNMP-MIB::ssRawContexts.0 Counter32: 718557 UCD-SNMP-MIB::ssCpuRawSoftIRQ.0 Counter32: 128 UCD-SNMP-MIB::ssRawSwapIn.0 Counter32: 0 UCD-SNMP-MIB::ssRawSwapOut.0 Counter32: 0 In particular the ssCpuRawUser ssCpuRawSystem ssCpuRawWait and ssCpuRawIdle OIDs provide counters which are helpful when determining whether a system is spending most of its processor time in kernel space user space or I/O. ssRawSwapIn and ssRawSwapOut can be helpful when determining whether a system is suffering from memory exhaustion. More memory information is available under the UCD-SNMP-MIB::memory OID which provides similar data to the free command: snmpwalk localhost UCD-SNMP-MIB::memory UCD-SNMP-MIB::memIndex.0 INTEGER: 0 UCD-SNMP-MIB::memErrorName.0 STRING: swap UCD-SNMP-MIB::memTotalSwap.0 INTEGER: 1023992 kB UCD-SNMP-MIB::memAvailSwap.0 INTEGER: 1023992 kB UCD-SNMP-MIB::memTotalReal.0 INTEGER: 1021588 kB UCD-SNMP-MIB::memAvailReal.0 INTEGER: 634260 kB UCD-SNMP-MIB::memTotalFree.0 INTEGER: 1658252 kB UCD-SNMP-MIB::memMinimumSwap.0 INTEGER: 16000 kB UCD-SNMP-MIB::memBuffer.0 INTEGER: 30760 kB UCD-SNMP-MIB::memCached.0 INTEGER: 216200 kB UCD-SNMP-MIB::memSwapError.0 INTEGER: noError0 UCD-SNMP-MIB::memSwapErrorMsg.0 STRING: Load averages are also available in the UCD SNMP MIB. The SNMP table UCD-SNMP- MIB::laTable has a listing of the 1 5 and 15 minute load averages: snmptable localhost UCD-SNMP-MIB::laTable SNMP table: UCD-SNMP-MIB::laTable laIndex laNames laLoad laConfig laLoadInt laLoadFloat laErrorFlag laErrMessage 1 Load-1 0.00 12.00 0 0.000000 noError 2 Load-5 0.00 12.00 0 0.000000 noError 3 Load-15 0.00 12.00 0 0.000000 noError 18.7.4.3. File Syst em and Disk Info rmat io n The Host Resources MIB provides information on file system size and usage. Each file system and also each memory pool has an entry in the HOST-RESOURCES-MIB::hrStorageTable table: snmptable -Cb localhost HOST-RESOURCES-MIB::hrStorageTable SNMP table: HOST-RESOURCES-MIB::hrStorageTable Index Type Descr AllocationUnits Size Used AllocationFailures 1 HOST-RESOURCES-TYPES::hrStorageRam Physical memory 1024 Bytes 1021588 388064 3 HOST-RESOURCES-TYPES::hrStorageVirtualMemory Virtual memory 1024 Bytes 2045580 388064 6 HOST-RESOURCES-TYPES::hrStorageOther Memory buffers Syst em Administ rat ors Guide 320

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1024 Bytes 1021588 31048 7 HOST-RESOURCES-TYPES::hrStorageOther Cached memory 1024 Bytes 216604 216604 10 HOST-RESOURCES-TYPES::hrStorageVirtualMemory Swap space 1024 Bytes 1023992 0 31 HOST-RESOURCES-TYPES::hrStorageFixedDisk / 4096 Bytes 2277614 250391 35 HOST-RESOURCES-TYPES::hrStorageFixedDisk /dev/shm 4096 Bytes 127698 0 36 HOST-RESOURCES-TYPES::hrStorageFixedDisk /boot 1024 Bytes 198337 26694 The OIDs under HOST-RESOURCES-MIB::hrStorageSize and HOST-RESOURCES- MIB::hrStorageUsed can be used to calculate the remaining capacity of each mounted file system. I/O data is available both in UCD-SNMP-MIB::systemStats ssIORawSent.0 and ssIORawRecieved.0 and in UCD-DISKIO-MIB::diskIOTable. The latter provides much more granular data. Under this table are OIDs for diskIONReadX and diskIONWrittenX which provide counters for the number of bytes read from and written to the block device in question since the system boot: snmptable -Cb localhost UCD-DISKIO-MIB::diskIOTable SNMP table: UCD-DISKIO-MIB::diskIOTable Index Device NRead NWritten Reads Writes LA1 LA5 LA15 NReadX NWrittenX ... 25 sda 216886272 139109376 16409 4894 216886272 139109376 26 sda1 2455552 5120 613 2 2455552 5120 27 sda2 1486848 0 332 0 1486848 0 28 sda3 212321280 139104256 15312 4871 212321280 139104256 18.7.4.4. Net wo rk Info rmat io n The Interfaces MIB provides information on network devices. IF-MIB::ifTable provides an SNMP table with an entry for each interface on the system the configuration of the interface and various packet counters for the interface. The following example shows the first few columns of ifTable on a system with two physical network interfaces: snmptable -Cb localhost IF-MIB::ifTable SNMP table: IF-MIB::ifTable Index Descr Type Mtu Speed PhysAddress AdminStatus 1 lo softwareLoopback 16436 10000000 up 2 eth0 ethernetCsmacd 1500 0 52:54:0:c7:69:58 up 3 eth1 ethernetCsmacd 1500 0 52:54:0:a7:a3:24 down Network traffic is available under the OIDs IF-MIB::ifOutOctets and IF-MIB::ifInOctets. The following SNMP queries will retrieve network traffic for each of the interfaces on this system: ⁠Chapt er 1 8 . Syst em Monit oring T ools 321

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snmpwalk localhost IF-MIB::ifDescr IF-MIB::ifDescr.1 STRING: lo IF-MIB::ifDescr.2 STRING: eth0 IF-MIB::ifDescr.3 STRING: eth1 snmpwalk localhost IF-MIB::ifOutOctets IF-MIB::ifOutOctets.1 Counter32: 10060699 IF-MIB::ifOutOctets.2 Counter32: 650 IF-MIB::ifOutOctets.3 Counter32: 0 snmpwalk localhost IF-MIB::ifInOctets IF-MIB::ifInOctets.1 Counter32: 10060699 IF-MIB::ifInOctets.2 Counter32: 78650 IF-MIB::ifInOctets.3 Counter32: 0 18.7.5. Extending Net-SNMP The Net-SNMP Agent can be extended to provide application metrics in addition to raw system metrics. This allows for capacity planning as well as performance issue troubleshooting. For example it may be helpful to know that an email system had a 5-minute load average of 15 while being tested but it is more helpful to know that the email system has a load average of 15 while processing 80000 messages a second. When application metrics are available via the same interface as the system metrics this also allows for the visualization of the impact of different load scenarios on system performance for example each additional 10000 messages increases the load average linearly until 100000. A number of the applications included in Red Hat Enterprise Linux extend the Net-SNMP Agent to provide application metrics over SNMP. There are several ways to extend the agent for custom applications as well. This section describes extending the agent with shell scripts and the Perl plug- ins from the Optional channel. It assumes that the net-snmp-utils and net-snmp-perl packages are installed and that the user is granted access to the SNMP tree as described in Section 18.7.3.2 “Configuring Authentication”. 18.7.5.1. Ext ending Net -SNMP wit h Shell Script s The Net-SNMP Agent provides an extension MIB NET-SNMP-EXTEND-MIB that can be used to query arbitrary shell scripts. To specify the shell script to run use the extend directive in the /etc/snmp/snmpd.conf file. Once defined the Agent will provide the exit code and any output of the command over SNMP. The example below demonstrates this mechanism with a script which determines the number of httpd processes in the process table. Note The Net-SNMP Agent also provides a built-in mechanism for checking the process table via the proc directive. See the snmpd.conf5 manual page for more information. The exit code of the following shell script is the number of httpd processes running on the system at a given point in time: /bin/sh NUMPIDS`pgrep httpd | wc -l` exit NUMPIDS Syst em Administ rat ors Guide 322

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To make this script available over SNMP copy the script to a location on the system path set the executable bit and add an extend directive to the /etc/snmp/snmpd.conf file. The format of the extend directive is the following: extend name prog args … where name is an identifying string for the extension prog is the program to run and args are the arguments to give the program. For instance if the above shell script is copied to /usr/local/bin/check_apache.sh the following directive will add the script to the SNMP tree: extend httpd_pids /bin/sh /usr/local/bin/check_apache.sh The script can then be queried at NET-SNMP-EXTEND-MIB::nsExtendObjects: snmpwalk localhost NET-SNMP-EXTEND-MIB::nsExtendObjects NET-SNMP-EXTEND-MIB::nsExtendNumEntries.0 INTEGER: 1 NET-SNMP-EXTEND-MIB::nsExtendCommand."httpd_pids" STRING: /bin/sh NET-SNMP-EXTEND-MIB::nsExtendArgs."httpd_pids" STRING: /usr/local/bin/check_apache.sh NET-SNMP-EXTEND-MIB::nsExtendInput."httpd_pids" STRING: NET-SNMP-EXTEND-MIB::nsExtendCacheTime."httpd_pids" INTEGER: 5 NET-SNMP-EXTEND-MIB::nsExtendExecType."httpd_pids" INTEGER: exec1 NET-SNMP-EXTEND-MIB::nsExtendRunType."httpd_pids" INTEGER: run-on- read1 NET-SNMP-EXTEND-MIB::nsExtendStorage."httpd_pids" INTEGER: permanent4 NET-SNMP-EXTEND-MIB::nsExtendStatus."httpd_pids" INTEGER: active1 NET-SNMP-EXTEND-MIB::nsExtendOutput1Line."httpd_pids" STRING: NET-SNMP-EXTEND-MIB::nsExtendOutputFull."httpd_pids" STRING: NET-SNMP-EXTEND-MIB::nsExtendOutNumLines."httpd_pids" INTEGER: 1 NET-SNMP-EXTEND-MIB::nsExtendResult."httpd_pids" INTEGER: 8 NET-SNMP-EXTEND-MIB::nsExtendOutLine."httpd_pids".1 STRING: Note that the exit code “8” in this example is provided as an INTEGER type and any output is provided as a STRING type. To expose multiple metrics as integers supply different arguments to the script using the extend directive. For example the following shell script can be used to determine the number of processes matching an arbitrary string and will also output a text string giving the number of processes: /bin/sh PATTERN1 NUMPIDS`pgrep PATTERN | wc -l` echo "There are NUMPIDS PATTERN processes." exit NUMPIDS The following /etc/snmp/snmpd.conf directives will give both the number of httpd PIDs as well as the number of snmpd PIDs when the above script is copied to /usr/local/bin/check_proc.sh: extend httpd_pids /bin/sh /usr/local/bin/check_proc.sh httpd extend snmpd_pids /bin/sh /usr/local/bin/check_proc.sh snmpd ⁠Chapt er 1 8 . Syst em Monit oring T ools 323

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The following example shows the output of an snmpwalk of the nsExtendObjects OID: snmpwalk localhost NET-SNMP-EXTEND-MIB::nsExtendObjects NET-SNMP-EXTEND-MIB::nsExtendNumEntries.0 INTEGER: 2 NET-SNMP-EXTEND-MIB::nsExtendCommand."httpd_pids" STRING: /bin/sh NET-SNMP-EXTEND-MIB::nsExtendCommand."snmpd_pids" STRING: /bin/sh NET-SNMP-EXTEND-MIB::nsExtendArgs."httpd_pids" STRING: /usr/local/bin/check_proc.sh httpd NET-SNMP-EXTEND-MIB::nsExtendArgs."snmpd_pids" STRING: /usr/local/bin/check_proc.sh snmpd NET-SNMP-EXTEND-MIB::nsExtendInput."httpd_pids" STRING: NET-SNMP-EXTEND-MIB::nsExtendInput."snmpd_pids" STRING: ... NET-SNMP-EXTEND-MIB::nsExtendResult."httpd_pids" INTEGER: 8 NET-SNMP-EXTEND-MIB::nsExtendResult."snmpd_pids" INTEGER: 1 NET-SNMP-EXTEND-MIB::nsExtendOutLine."httpd_pids".1 STRING: There are 8 httpd processes. NET-SNMP-EXTEND-MIB::nsExtendOutLine."snmpd_pids".1 STRING: There are 1 snmpd processes. Warning Integer exit codes are limited to a range of 0–255. For values that are likely to exceed 256 either use the standard output of the script which will be typed as a string or a different method of extending the agent. This last example shows a query for the free memory of the system and the number of httpd processes. This query could be used during a performance test to determine the impact of the number of processes on memory pressure: snmpget localhost \ NET-SNMP-EXTEND-MIB::nsExtendResult."httpd_pids" \ UCD-SNMP-MIB::memAvailReal.0 NET-SNMP-EXTEND-MIB::nsExtendResult."httpd_pids" INTEGER: 8 UCD-SNMP-MIB::memAvailReal.0 INTEGER: 799664 kB 18.7.5.2. Ext ending Net -SNMP wit h Perl Executing shell scripts using the extend directive is a fairly limited method for exposing custom application metrics over SNMP. The Net-SNMP Agent also provides an embedded Perl interface for exposing custom objects. The net-snmp-perl package in the Optional channel provides the NetSNMP::agent Perl module that is used to write embedded Perl plug-ins on Red Hat Enterprise Linux. Note Before subscribing to the Optional and Supplementary channels see the Scope of Coverage Details. If you decide to install packages from these channels follow the steps documented in the article called How to access Optional and Supplementary channels and -devel packages using Red Hat Subscription Manager RHSM on the Red Hat Customer Portal. Syst em Administ rat ors Guide 324

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The NetSNMP::agent Perl module provides an agent object which is used to handle requests for a part of the agents OID tree. The agent objects constructor has options for running the agent as a sub-agent of snmpd or a standalone agent. No arguments are necessary to create an embedded agent: use NetSNMP::agent :all my agent new NetSNMP::agent The agent object has a register method which is used to register a callback function with a particular OID. The register function takes a name OID and pointer to the callback function. The following example will register a callback function named hello_handler with the SNMP Agent which will handle requests under the OID .1.3.6.1.4.1.8072.9999.9999: agent-register"hello_world" ".1.3.6.1.4.1.8072.9999.9999" \hello_handler Note The OID .1.3.6.1.4.1.8072.9999.9999 NET-SNMP-MIB::netSnmpPlaypen is typically used for demonstration purposes only. If your organization does not already have a root OID you can obtain one by contacting an ISO Name Registration Authority ANSI in the United States. The handler function will be called with four parameters HANDLER REGISTRATION_INFO REQUEST_INFO and REQUESTS. The REQUESTS parameter contains a list of requests in the current call and should be iterated over and populated with data. The request objects in the list have get and set methods which allow for manipulating the OID and value of the request. For example the following call will set the value of a request object to the string “hello world”: request-setValueASN_OCTET_STR "hello world" The handler function should respond to two types of SNMP requests: the GET request and the GETNEXT request. The type of request is determined by calling the getMode method on the request_info object passed as the third parameter to the handler function. If the request is a GET request the caller will expect the handler to set the value of the request object depending on the OID of the request. If the request is a GETNEXT request the caller will also expect the handler to set the OID of the request to the next available OID in the tree. This is illustrated in the following code example: my request my string_value "hello world" my integer_value "8675309" forrequest requests request request request-next my oid request-getOID if request_info-getMode MODE_GET if oid new NetSNMP::OID".1.3.6.1.4.1.8072.9999.9999.1.0" request-setValueASN_OCTET_STR string_value elsif oid new NetSNMP::OID".1.3.6.1.4.1.8072.9999.9999.1.1" request-setValueASN_INTEGER integer_value ⁠Chapt er 1 8 . Syst em Monit oring T ools 325

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elsif request_info-getMode MODE_GETNEXT if oid new NetSNMP::OID".1.3.6.1.4.1.8072.9999.9999.1.0" request-setOID".1.3.6.1.4.1.8072.9999.9999.1.1" request-setValueASN_INTEGER integer_value elsif oid new NetSNMP::OID".1.3.6.1.4.1.8072.9999.9999.1.0" request-setOID".1.3.6.1.4.1.8072.9999.9999.1.0" request-setValueASN_OCTET_STR string_value When getMode returns MODE_GET the handler analyzes the value of the getOID call on the request object. The value of the request is set to either string_value if the OID ends in “.1.0” or set to integer_value if the OID ends in “.1.1”. If the getMode returns MODE_GETNEXT the handler determines whether the OID of the request is “.1.0” and then sets the OID and value for “.1.1”. If the request is higher on the tree than “.1.0” the OID and value for “.1.0” is set. This in effect returns the “next” value in the tree so that a program like snmpwalk can traverse the tree without prior knowledge of the structure. The type of the variable is set using constants from NetSNMP::ASN. See the perldoc for NetSNMP::ASN for a full list of available constants. The entire code listing for this example Perl plug-in is as follows: /usr/bin/perl use NetSNMP::agent :all use NetSNMP::ASN qwASN_OCTET_STR ASN_INTEGER sub hello_handler my handler registration_info request_info requests _ my request my string_value "hello world" my integer_value "8675309" forrequest requests request request request-next my oid request-getOID if request_info-getMode MODE_GET if oid new NetSNMP::OID".1.3.6.1.4.1.8072.9999.9999.1.0" request-setValueASN_OCTET_STR string_value elsif oid new NetSNMP::OID".1.3.6.1.4.1.8072.9999.9999.1.1" request-setValueASN_INTEGER integer_value elsif request_info-getMode MODE_GETNEXT if oid new NetSNMP::OID".1.3.6.1.4.1.8072.9999.9999.1.0" request-setOID".1.3.6.1.4.1.8072.9999.9999.1.1" request-setValueASN_INTEGER integer_value elsif oid new NetSNMP::OID".1.3.6.1.4.1.8072.9999.9999.1.0" request-setOID".1.3.6.1.4.1.8072.9999.9999.1.0" request-setValueASN_OCTET_STR string_value Syst em Administ rat ors Guide 326

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my agent new NetSNMP::agent agent-register"hello_world" ".1.3.6.1.4.1.8072.9999.9999" \hello_handler To test the plug-in copy the above program to /usr/share/snmp/hello_world.pl and add the following line to the /etc/snmp/snmpd.conf configuration file: perl do "/usr/share/snmp/hello_world.pl" The SNMP Agent Daemon will need to be restarted to load the new Perl plug-in. Once it has been restarted an snmpwalk should return the new data: snmpwalk localhost NET-SNMP-MIB::netSnmpPlaypen NET-SNMP-MIB::netSnmpPlaypen.1.0 STRING: "hello world" NET-SNMP-MIB::netSnmpPlaypen.1.1 INTEGER: 8675309 The snmpget should also be used to exercise the other mode of the handler: snmpget localhost \ NET-SNMP-MIB::netSnmpPlaypen.1.0 \ NET-SNMP-MIB::netSnmpPlaypen.1.1 NET-SNMP-MIB::netSnmpPlaypen.1.0 STRING: "hello world" NET-SNMP-MIB::netSnmpPlaypen.1.1 INTEGER: 8675309 18.8. Additional Resources To learn more about gathering system information see the following resources. 18.8.1. Installed Documentation lscpu1 — The manual page for the lscpu command. lsusb8 — The manual page for the lsusb command. findmnt8 — The manual page for the findmnt command. blkid8 — The manual page for the blkid command. lsblk8 — The manual page for the lsblk command. ps1 — The manual page for the ps command. top1 — The manual page for the top command. free1 — The manual page for the free command. df1 — The manual page for the df command. du1 — The manual page for the du command. ⁠Chapt er 1 8 . Syst em Monit oring T ools 327

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lspci8 — The manual page for the lspci command. snmpd8 — The manual page for the snmpd service. snmpd.conf5 — The manual page for the /etc/snmp/snmpd.conf file containing full documentation of available configuration directives. Syst em Administ rat ors Guide 328

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Chapter 19. OpenLMI The Open Linux Management Infrastructure commonly abbreviated as OpenLMI is a common infrastructure for the management of Linux systems. It builds on top of existing tools and serves as an abstraction layer in order to hide much of the complexity of the underlying system from system administrators. OpenLMI is distributed with a set of services that can be accessed locally or remotely and provides multiple language bindings standard APIs and standard scripting interfaces that can be used to manage and monitor hardware operating systems and system services. 19.1. About OpenLMI OpenLMI is designed to provide a common management interface to production servers running the Red Hat Enterprise Linux system on both physical and virtual machines. It consists of the following three components: 1. System management agents — these agents are installed on a managed system and implement an object model that is presented to a standard object broker. The initial agents implemented in OpenLMI include storage configuration and network configuration but later work will address additional elements of system management. The system management agents are commonly referred to as Common Information Model providers or CIM providers. 2. A standard object broker — the object broker manages system management agents and provides an interface to them. The standard object broker is also known as a CIM Object Monitor or CIMOM. 3. Client applications and scripts — the client applications and scripts call the system management agents through the standard object broker. The OpenLMI project complements existing management initiatives by providing a low-level interface that can be used by scripts or system management consoles. Interfaces distributed with OpenLMI include C C++ Python Java and an interactive command line client and all of them offer the same full access to the capabilities implemented in each agent. This ensures that you always have access to exactly the same capabilities no matter which programming interface you decide to use. 19.1.1. Main Features The following are key benefits of installing and using OpenLMI on your system: OpenLMI provides a standard interface for configuration management and monitoring of your local and remote systems. It allows you to configure manage and monitor production servers running on both physical and virtual machines. It is distributed with a collection of CIM providers that allow you to configure manage and monitor storage devices and complex networks. It allows you to call system management functions from C C++ Python and Java programs and includes LMIShell which provides a command line interface. It is free software based on open industry standards. 19.1.2. Management Capabilities Key capabilities of OpenLMI include the management of storage devices networks system services user accounts hardware and software configuration power management and interaction with Active ⁠Chapt er 1 9 . OpenLMI 329

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Directory. For a complete list of CIM providers that are distributed with Red Hat Enterprise Linux 7 see Table 19.1 “Available CIM Providers”. Table 19 .1. Available CIM Providers Package Name Description openlmi-account A CIM provider for managing user accounts. openlmi-logicalfile A CIM provider for reading files and directories. openlmi-networking A CIM provider for network management. openlmi-powermanagement A CIM provider for power management. openlmi-service A CIM provider for managing system services. openlmi-storage A CIM provider for storage management. openlmi-fan A CIM provider for controlling computer fans. openlmi-hardware A CIM provider for retrieving hardware information. openlmi-realmd A CIM provider for configuring realmd. openlmi-software ⁠ A CIM provider for software management. 19.2. Installing OpenLMI OpenLMI is distributed as a collection of RPM packages that include the CIMOM individual CIM providers and client applications. This allows you distinguish between a managed and client system and install only those components you need. 19.2.1. Installing OpenLMI on a Managed System A managed system is the system you intend to monitor and manage by using the OpenLMI client tools. To install OpenLMI on a managed system complete the following steps: 1. Install the tog-pegasus package by typing the following at a shell prompt as root: yum install tog-pegasus This command installs the OpenPegasus CIMOM and all its dependencies to the system and creates a user account for the pegasus user. 2. Install required CIM providers by running the following command as root: yum install openlmi- storagenetworkingserviceaccountpowermanagement This command installs the CIM providers for storage network service account and power management. For a complete list of CIM providers distributed with Red Hat Enterprise Linux 7 see Table 19.1 “Available CIM Providers”. 3. Edit the /etc/Pegasus/access.conf configuration file to customize the list of users that are allowed to connect to the OpenPegasus CIMOM. By default only the pegasus user is allowed to access the CIMOM both remotely and locally. To activate this user account run the following command as root to set the users password: a a In Red Hat Enterp rise Linux 7 the Op enLMI So ftware p ro vid er is includ ed as a Techno lo g y Preview. This p ro vid er is fully functio nal b ut has a kno wn p erfo rmance scaling issue where listing larg e numb ers o f so ftware p ackag es may co nsume excessive amo unt o f memo ry and time. To wo rk aro und this issue ad just p ackag e searches to return as few p ackag es as p o ssib le. Syst em Administ rat ors Guide 330

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passwd pegasus 4. Start the OpenPegasus CIMOM by activating the tog-pegasus.service unit. To activate the tog-pegasus.service unit in the current session type the following at a shell prompt as root: systemctl start tog-pegasus.service To configure the tog-pegasus.service unit to start automatically at boot time type as root: systemctl enable tog-pegasus.service 5. If you intend to interact with the managed system from a remote machine enable TCP communication on port 5989 wbem-https. To open this port in the current session run the following command as root: firewall-cmd --add-port 5989/tcp To open port 5989 for TCP communication permanently type as root: firewall-cmd --permanent --add-port 5989/tcp You can now connect to the managed system and interact with it by using the OpenLMI client tools as described in Section 19.4 “Using LMIShell”. If you intend to perform OpenLMI operations directly on the managed system also complete the steps described in Section 19.2.2 “Installing OpenLMI on a Client System”. 19.2.2. Installing OpenLMI on a Client System A client system is the system from which you intend to interact with the managed system. In a typical scenario the client system and the managed system are installed on two separate machines but you can also install the client tools on the managed system and interact with it directly. To install OpenLMI on a client system complete the following steps: 1. Install the openlmi-tools package by typing the following at a shell prompt as root: yum install openlmi-tools This command installs LMIShell an interactive client and interpreter for accessing CIM objects provided by OpenPegasus and all its dependencies to the system. 2. Configure SSL certificates for OpenPegasus as described in Section 19.3 “Configuring SSL Certificates for OpenPegasus”. You can now use the LMIShell client to interact with the managed system as described in Section 19.4 “Using LMIShell”. 19.3. Configuring SSL Certificates for OpenPegasus ⁠Chapt er 1 9 . OpenLMI 331

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OpenLMI uses the Web-Based Enterprise Management WBEM protocol that functions over an HTTP transport layer. Standard HTTP Basic authentication is performed in this protocol which means that the user name and password are transmitted alongside the requests. Configuring the OpenPegasus CIMOM to use HTTPS for communication is necessary to ensure secure authentication. A Secure Sockets Layer SSL or Transport Layer Security TLS certificate is required on the managed system to establish an encrypted channel. There are two ways of managing SSL/TLS certificates on a system: Self-signed certificates require less infrastructure to use but are more difficult to deploy to clients and manage securely. Authority-signed certificates are easier to deploy to clients once they are set up but may require a greater initial investment. When using an authority-signed certificate it is necessary to configure a trusted certificate authority on the client systems. The authority can then be used for signing all of the managed systems CIMOM certificates. Certificates can also be part of a certificate chain so the certificate used for signing the managed systems certificates may in turn be signed by another higher authority such as Verisign CAcert RSA and many others. The default certificate and trust store locations on the file system are listed in Table 19.2 “Certificate and Trust Store Locations”. Table 19 .2. Certificate and Trust Store Locations Configuration Option Location Description sslCertificateFilePa th /etc/Pegasus/server.p em Public certificate of the CIMOM. sslKeyFilePath /etc/Pegasus/file.pe m Private key known only to the CIMOM. sslTrustStore /etc/Pegasus/client. pem The file or directory providing the list of trusted certificate authorities. Important If you modify any of the files mentioned in Table 19.2 “Certificate and Trust Store Locations” restart the tog-pegasus service to make sure it recognizes the new certificates. To restart the service type the following at a shell prompt as root: systemctl restart tog-pegasus.service For more information on how to manage system services in Red Hat Enterprise Linux 7 see Chapter 9 Managing Services with systemd. 19.3.1. Managing Self-signed Certificates A self-signed certificate uses its own private key to sign itself and it is not connected to any chain of trust. On a managed system if certificates have not been provided by the administrator prior to the first time that the tog-pegasus service is started a set of self-signed certificates will be automatically generated using the systems primary hostname as the certificate subject. Syst em Administ rat ors Guide 332

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Important The automatically generated self-signed certificates are valid by default for 10 years but they have no automatic-renewal capability. Any modification to these certificates will require manually creating new certificates following guidelines provided by the OpenSSL or Mozilla NSS documentation on the subject. To configure client systems to trust the self-signed certificate complete the following steps: 1. Copy the /etc/Pegasus/server.pem certificate from the managed system to the /etc/pki/ca-trust/source/anchors/ directory on the client system. To do so type the following at a shell prompt as root: scp roothostname:/etc/Pegasus/server.pem /etc/pki/ca- trust/source/anchors/pegasus-hostname.pem Replace hostname with the host name of the managed system. Note that this command only works if the sshd service is running on the managed system and is configured to allow the root user to log in to the system over the SSH protocol. For more information on how to install and configure the sshd service and use the scp command to transfer files over the SSH protocol see Chapter 10 OpenSSH. 2. Verify the integrity of the certificate on the client system by comparing its checksum with the checksum of the original file. To calculate the checksum of the /etc/Pegasus/server.pem file on the managed system run the following command as root on that system: sha1sum /etc/Pegasus/server.pem To calculate the checksum of the /etc/pki/ca- trust/source/anchors/pegasus-hostname.pem file on the client system run the following command on this system: sha1sum /etc/pki/ca-trust/source/anchors/pegasus-hostname.pem Replace hostname with the host name of the managed system. 3. Update the trust store on the client system by running the following command as root: update-ca-trust extract 19.3.2. Managing Authority-signed Certificates with Identity Management Recommended The Identity Management feature of Red Hat Enterprise Linux provides a domain controller which simplifies the management of SSL certificates within systems joined to the domain. Among others the Identity Management server provides an embedded Certificate Authority. See the Red Hat Enterprise Linux 7 Linux Domain Identity Authentication and Policy Guide or the FreeIPA documentation for information on how to join the client and managed systems to the domain. It is necessary to register the managed system to Identity Management for client systems the registration is optional. The following steps are required on the managed system: ⁠Chapt er 1 9 . OpenLMI 333

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1. Install the ipa-client package and register the system to Identity Management as described in the Red Hat Enterprise Linux 7 Linux Domain Identity Authentication and Policy Guide. 2. Copy the Identity Management signing certificate to the trusted store by typing the following command as root: cp /etc/ipa/ca.crt /etc/pki/ca-trust/source/anchors/ipa.crt 3. Update the trust store by running the following command as root: update-ca-trust extract 4. Register Pegasus as a service in the Identity Management domain by running the following command as a privileged domain user: ipa service-add CIMOM/hostname Replace hostname with the host name of the managed system. This command can be run from any system in the Identity Management domain that has the ipa-admintools package installed. It creates a service entry in Identity Management that can be used to generate signed SSL certificates. 5. Back up the PEM files located in the /etc/Pegasus/ directory recommended. 6. Retrieve the signed certificate by running the following command as root: ipa-getcert request -f /etc/Pegasus/server.pem -k /etc/Pegasus/file.pem -N CNhostname -K CIMOM/hostname Replace hostname with the host name of the managed system. The certificate and key files are now kept in proper locations. The certmonger daemon installed on the managed system by the ipa-client-install script ensures that the certificate is kept up-to-date and renewed as necessary. For more information see the Red Hat Enterprise Linux 7 Linux Domain Identity Authentication and Policy Guide. To register the client system and update the trust store follow the steps below. 1. Install the ipa-client package and register the system to Identity Management as described in the Red Hat Enterprise Linux 7 Linux Domain Identity Authentication and Policy Guide. 2. Copy the Identity Management signing certificate to the trusted store by typing the following command as root: cp /etc/ipa/ca.crt /etc/pki/ca-trust/source/anchors/ipa.crt 3. Update the trust store by running the following command as root: update-ca-trust extract If the client system is not meant to be registered in Identity Management complete the following steps to update the trust store. Syst em Administ rat ors Guide 334

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1. Copy the /etc/ipa/ca.crt file securely from any other system joined to the same Identity Management domain to the trusted store /etc/pki/ca-trust/source/anchors/ directory as root. 2. Update the trust store by running the following command as root: update-ca-trust extract 19.3.3. Managing Authority-signed Certificates Manually Managing authority-signed certificates with other mechanisms than Identity Management requires more manual configuration. It is necessary to ensure that all of the clients trust the certificate of the authority that will be signing the managed system certificates: If a certificate authority is trusted by default it is not necessary to perform any particular steps to accomplish this. If the certificate authority is not trusted by default the certificate has to be imported on the client and managed systems. Copy the certificate to the trusted store by typing the following command as root: cp /path/to/ca.crt /etc/pki/ca-trust/source/anchors/ca.crt Update the trust store by running the following command as root: update-ca-trust extract On the managed system complete the following steps: 1. Create a new SSL configuration file /etc/Pegasus/ssl.cnf to store information about the certificate. The contents of this file must be similar to the following example: req distinguished_name req_distinguished_name prompt no req_distinguished_name C US ST Massachusetts L Westford O Fedora OU Fedora OpenLMI CN hostname Replace hostname with the fully qualified domain name of the managed system. 2. Generate a private key on the managed system by using the following command as root: openssl genrsa -out /etc/Pegasus/file.pem 1024 3. Generate a certificate signing request CSR by running this command as root: ⁠Chapt er 1 9 . OpenLMI 335

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openssl req -config /etc/Pegasus/ssl.cnf -new -key /etc/Pegasus/file.pem -out /etc/Pegasus/server.csr 4. Send the /etc/Pegasus/server.csr file to the certificate authority for signing. The detailed procedure of submitting the file depends on the particular certificate authority. 5. When the signed certificate is received from the certificate authority save it as /etc/Pegasus/server.pem. 6. Copy the certificate of the trusted authority to the Pegasus trust store to make sure that Pegasus is capable of trusting its own certificate by running as root: cp /path/to/ca.crt /etc/Pegasus/client.pem After accomplishing all the described steps the clients that trust the signing authority are able to successfully communicate with the managed servers CIMOM. Important Unlike the Identity Management solution if the certificate expires and needs to be renewed all of the described manual steps have to be carried out again. It is recommended to renew the certificates before they expire. 19.4. Using LMIShell LMIShell is an interactive client and non-interactive interpreter that can be used to access CIM objects provided by the OpenPegasus CIMOM. It is based on the Python interpreter but also implements additional functions and classes for interacting with CIM objects. 19.4 .1. Starting Using and Exiting LMIShell Similarly to the Python interpreter you can use LMIShell either as an interactive client or as a non- interactive interpreter for LMIShell scripts. St art ing LMIShell in Int eract ive Mo de To start the LMIShell interpreter in interactive mode run the lmishell command with no additional arguments: lmishell By default when LMIShell attempts to establish a connection with a CIMOM it validates the server- side certificate against the Certification Authorities trust store. To disable this validation run the lmishell command with the --noverify or -n command line option: lmishell --noverify Using T ab Co mplet io n Syst em Administ rat ors Guide 336

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When running in interactive mode the LMIShell interpreter allows you press the Tab key to complete basic programming structures and CIM objects including namespaces classes methods and object properties. Bro wsing Hist o ry By default LMIShell stores all commands you type at the interactive prompt in the /.lmishell_history file. This allows you to browse the command history and re-use already entered lines in interactive mode without the need to type them at the prompt again. To move backward in the command history press the Up Arrow key or the Ctrl+p key combination. To move forward in the command history press the Down Arrow key or the Ctrl+n key combination. LMIShell also supports an incremental reverse search. To look for a particular line in the command history press Ctrl+r and start typing any part of the command. For example: reverse-i-search`connect: c connect"server.example.com" "pegasus" To clear the command history use the clear_history function as follows: clear_history You can configure the number of lines that are stored in the command history by changing the value of the history_length option in the /.lmishellrc configuration file. In addition you can change the location of the history file by changing the value of the history_file option in this configuration file. For example to set the location of the history file to /.lmishell_history and configure LMIShell to store the maximum of 1000 lines in it add the following lines to the /.lmishellrc file: history_file "/.lmishell_history" history_length 1000 Handling Except io ns By default the LMIShell interpreter handles all exceptions and uses return values. To disable this behavior in order to handle all exceptions in the code use the use_exceptions function as follows: use_exceptions To re-enable the automatic exception handling use: use_exceptionFalse You can permanently disable the exception handling by changing the value of the use_exceptions option in the /.lmishellrc configuration file to True: use_exceptions True Co nfiguring a T empo rary Cache ⁠Chapt er 1 9 . OpenLMI 337

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With the default configuration LMIShell connection objects use a temporary cache for storing CIM class names and CIM classes in order to reduce network communication. To clear this temporary cache use the clear_cache method as follows: object_name.clear_cache Replace object_name with the name of a connection object. To disable the temporary cache for a particular connection object use the use_cache method as follows: object_name.use_cacheFalse To enable it again use: object_name.use_cacheTrue You can permanently disable the temporary cache for connection objects by changing the value of the use_cache option in the /.lmishellrc configuration file to False: use_cache False Exit ing LMIShell To terminate the LMIShell interpreter and return to the shell prompt press the Ctrl+d key combination or issue the quit function as follows: quit Running an LMIShell Script To run an LMIShell script run the lmishell command as follows: lmishell file_name Replace file_name with the name of the script. To inspect an LMIShell script after its execution also specify the --interact or -i command line option: lmishell --interact file_name The preferred file extension of LMIShell scripts is .lmi. 19.4 .2. Connecting to a CIMOM LMIShell allows you to connect to a CIMOM that is running either locally on the same system or on a remote machine accessible over the network. Co nnect ing t o a Remo t e CIMOM To access CIM objects provided by a remote CIMOM create a connection object by using the connect function as follows: Syst em Administ rat ors Guide 338

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connecthost_name user_name password Replace host_name with the host name of the managed system user_name with the name of a user that is allowed to connect to the OpenPegasus CIMOM running on that system and password with the users password. If the password is omitted LMIShell prompts the user to enter it. The function returns an LMIConnection object. Example 19 .1. Connecting to a Remote CIMOM To connect to the OpenPegasus CIMOM running on server.example.com as user pegasus type the following at the interactive prompt: c connect"server.example.com" "pegasus" password: Co nnect ing t o a Lo cal CIMOM LMIShell allows you to connect to a local CIMOM by using a Unix socket. For this type of connection you must run the LMIShell interpreter as the root user and the /var/run/tog- pegasus/cimxml.socket socket must exist. To access CIM objects provided by a local CIMOM create a connection object by using the connect function as follows: connecthost_name Replace host_name with localhost 127.0.0.1 or ::1. The function returns an LMIConnection object or None. Example 19 .2. Connecting to a Local CIMOM To connect to the OpenPegasus CIMOM running on localhost as the root user type the following at the interactive prompt: c connect"localhost" Verifying a Co nnect io n t o a CIMOM The connect function returns either an LMIConnection object or None if the connection could not be established. In addition when the connect function fails to establish a connection it prints an error message to standard error output. To verify that a connection to a CIMOM has been established successfully use the isinstance function as follows: isinstanceobject_name LMIConnection ⁠Chapt er 1 9 . OpenLMI 339

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Replace object_name with the name of the connection object. This function returns True if object_name is an LMIConnection object or False otherwise. Example 19 .3. Verifying a Connection to a CIMOM To verify that the c variable created in Example 19.1 “Connecting to a Remote CIMOM” contains an LMIConnection object type the following at the interactive prompt: isinstancec LMIConnection True Alternatively you can verify that c is not None: c is None False 19.4 .3. Working with Namespaces LMIShell namespaces provide a natural means of organizing available classes and serve as a hierarchic access point to other namespaces and classes. The root namespace is the first entry point of a connection object. List ing Available Namespaces To list all available namespaces use the print_namespaces method as follows: object_name.print_namespaces Replace object_name with the name of the object to inspect. This method prints available namespaces to standard output. To get a list of available namespaces access the object attribute namespaces: object_name.namespaces This returns a list of strings. Example 19 .4 . Listing Available Namespaces To inspect the root namespace object of the c connection object created in Example 19.1 “Connecting to a Remote CIMOM” and list all available namespaces type the following at the interactive prompt: c.root.print_namespaces cimv2 interop PG_InterOp PG_Internal Syst em Administ rat ors Guide 34 0

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To assign a list of these namespaces to a variable named root_namespaces type: root_namespaces c.root.namespaces Accessing Namespace Object s To access a particular namespace object use the following syntax: object_name.namespace_name Replace object_name with the name of the object to inspect and namespace_name with the name of the namespace to access. This returns an LMINamespace object. Example 19 .5. Accessing Namespace Objects To access the cimv2 namespace of the c connection object created in Example 19.1 “Connecting to a Remote CIMOM” and assign it to a variable named ns type the following at the interactive prompt: ns c.root.cimv2 19.4 .4 . Working with Classes LMIShell classes represent classes provided by a CIMOM. You can access and list their properties methods instances instance names and ValueMap properties print their documentation strings and create new instances and instance names. List ing Available Classes To list all available classes in a particular namespace use the print_classes method as follows: namespace_object.print_classes Replace namespace_object with the namespace object to inspect. This method prints available classes to standard output. To get a list of available classes use the classes method: namespace_object.classes This method returns a list of strings. Example 19 .6 . Listing Available Classes To inspect the ns namespace object created in Example 19.5 “Accessing Namespace Objects” and list all available classes type the following at the interactive prompt: ⁠Chapt er 1 9 . OpenLMI 34 1

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ns.print_classes CIM_CollectionInSystem CIM_ConcreteIdentity CIM_ControlledBy CIM_DeviceSAPImplementation CIM_MemberOfStatusCollection ... To assign a list of these classes to a variable named cimv2_classes type: cimv2_classes ns.classes Accessing Class Object s To access a particular class object that is provided by the CIMOM use the following syntax: namespace_object.class_name Replace namespace_object with the name of the namespace object to inspect and class_name with the name of the class to access. Example 19 .7. Accessing Class Objects To access the LMI_IPNetworkConnection class of the ns namespace object created in Example 19.5 “Accessing Namespace Objects” and assign it to a variable named cls type the following at the interactive prompt: cls ns.LMI_IPNetworkConnection Examining Class Object s All class objects store information about their name and the namespace they belong to as well as detailed class documentation. To get the name of a particular class object use the following syntax: class_object.classname Replace class_object with the name of the class object to inspect. This returns a string representation of the object name. To get information about the namespace a class object belongs to use: class_object.namespace This returns a string representation of the namespace. To display detailed class documentation use the doc method as follows: class_object.doc Syst em Administ rat ors Guide 34 2

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Example 19 .8. Examining Class Objects To inspect the cls class object created in Example 19.7 “Accessing Class Objects” and display its name and corresponding namespace type the following at the interactive prompt: cls.classname LMI_IPNetworkConnection cls.namespace root/cimv2 To access class documentation type: cls.doc Class: LMI_IPNetworkConnection SuperClass: CIM_IPNetworkConnection qualifier string UMLPackagePath: CIM::Network::IP qualifier string Version: 0.1.0 ... List ing Available Met ho ds To list all available methods of a particular class object use the print_methods method as follows: class_object.print_methods Replace class_object with the name of the class object to inspect. This method prints available methods to standard output. To get a list of available methods use the methods method: class_object.methods This method returns a list of strings. Example 19 .9 . Listing Available Methods To inspect the cls class object created in Example 19.7 “Accessing Class Objects” and list all available methods type the following at the interactive prompt: cls.print_methods RequestStateChange To assign a list of these methods to a variable named service_methods type: service_methods cls.methods ⁠Chapt er 1 9 . OpenLMI 34 3

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List ing Available Pro pert ies To list all available properties of a particular class object use the print_properties method as follows: class_object.print_properties Replace class_object with the name of the class object to inspect. This method prints available properties to standard output. To get a list of available properties use the properties method: class_object.properties This method returns a list of strings. Example 19 .10. Listing Available Properties To inspect the cls class object created in Example 19.7 “Accessing Class Objects” and list all available properties type the following at the interactive prompt: cls.print_properties RequestedState HealthState StatusDescriptions TransitioningToState Generation ... To assign a list of these classes to a variable named service_properties type: service_properties cls.properties List ing and Viewing ValueMap Pro pert ies CIM classes may contain ValueMap properties in their Managed Object Format MOF definition. ValueMap properties contain constant values which may be useful when calling methods or checking returned values. To list all available ValueMap properties of a particular class object use the print_valuemap_properties method as follows: class_object.print_valuemap_properties Replace class_object with the name of the class object to inspect. This method prints available ValueMap properties to standard output: To get a list of available ValueMap properties use the valuemap_properties method: Syst em Administ rat ors Guide 34 4

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class_object.valuemap_properties This method returns a list of strings. Example 19 .11. Listing ValueMap Properties To inspect the cls class object created in Example 19.7 “Accessing Class Objects” and list all available ValueMap properties type the following at the interactive prompt: cls.print_valuemap_properties RequestedState HealthState TransitioningToState DetailedStatus OperationalStatus ... To assign a list of these ValueMap properties to a variable named service_valuemap_properties type: service_valuemap_properties cls.valuemap_properties To access a particular ValueMap property use the following syntax: class_object.valuemap_propertyValues Replace valuemap_property with the name of the ValueMap property to access. To list all available constant values use the print_values method as follows: class_object.valuemap_propertyValues.print_values This method prints available named constant values to standard output. You can also get a list of available constant values by using the values method: class_object.valuemap_propertyValues.values This method returns a list of strings. Example 19 .12. Accessing ValueMap Properties Example 19.11 “Listing ValueMap Properties” mentions a ValueMap property named RequestedState. To inspect this property and list available constant values type the following at the interactive prompt: cls.RequestedStateValues.print_values Reset NoChange NotApplicable ⁠Chapt er 1 9 . OpenLMI 34 5

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Quiesce Unknown ... To assign a list of these constant values to a variable named requested_state_values type: requested_state_values cls.RequestedStateValues.values To access a particular constant value use the following syntax: class_object.valuemap_propertyValues.constant_value_name Replace constant_value_name with the name of the constant value. Alternatively you can use the value method as follows: class_object.valuemap_propertyValues.value"constant_value_name" To determine the name of a particular constant value use the value_name method: class_object.valuemap_propertyValues.value_name"constant_value" This method returns a string. Example 19 .13. Accessing Constant Values Example 19.12 “Accessing ValueMap Properties” shows that the RequestedState property provides a constant value named Reset. To access this named constant value type the following at the interactive prompt: cls.RequestedStateValues.Reset 11 cls.RequestedStateValues.value"Reset" 11 To determine the name of this constant value type: cls.RequestedStateValues.value_name11 uReset Fet ching a CIMClass Object Many class methods do not require access to a CIMClass object which is why LMIShell only fetches this object from the CIMOM when a called method actually needs it. To fetch the CIMClass object manually use the fetch method as follows: class_object.fetch Syst em Administ rat ors Guide 34 6

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Replace class_object with the name of the class object. Note that methods that require access to a CIMClass object fetch it automatically. 19.4 .5. Working with Instances LMIShell instances represent instances provided by a CIMOM. You can get and set their properties list and call their methods print their documentation strings get a list of associated or association objects push modified objects to the CIMOM and delete individual instances from the CIMOM. Accessing Inst ances To get a list of all available instances of a particular class object use the instances method as follows: class_object.instances Replace class_object with the name of the class object to inspect. This method returns a list of LMIInstance objects. To access the first instance of a class object use the first_instance method: class_object.first_instance This method returns an LMIInstance object. In addition to listing all instances or returning the first one both instances and first_instance support an optional argument to allow you to filter the results: class_object.instancescriteria class_object.first_instancecriteria Replace criteria with a dictionary consisting of key-value pairs where keys represent instance properties and values represent required values of these properties. Example 19 .14 . Accessing Instances To find the first instance of the cls class object created in Example 19.7 “Accessing Class Objects” that has the ElementName property equal to eth0 and assign it to a variable named device type the following at the interactive prompt: device cls.first_instance"ElementName": "eth0" Examining Inst ances All instance objects store information about their class name and the namespace they belong to as well as detailed documentation about their properties and values. In addition instance objects allow you to retrieve a unique identification object. To get the class name of a particular instance object use the following syntax: ⁠Chapt er 1 9 . OpenLMI 34 7

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instance_object.classname Replace instance_object with the name of the instance object to inspect. This returns a string representation of the class name. To get information about the namespace an instance object belongs to use: instance_object.namespace This returns a string representation of the namespace. To retrieve a unique identification object for an instance object use: instance_object.path This returns an LMIInstanceName object. Finally to display detailed documentation use the doc method as follows: instance_object.doc Example 19 .15. Examining Instances To inspect the device instance object created in Example 19.14 “Accessing Instances” and display its class name and the corresponding namespace type the following at the interactive prompt: device.classname uLMI_IPNetworkConnection device.namespace root/cimv2 To access instance object documentation type: device.doc Instance of LMI_IPNetworkConnection property uint16 RequestedState 12 property uint16 HealthState property array string StatusDescriptions ... Creat ing New Inst ances Certain CIM providers allow you to create new instances of specific classes objects. To create a new instance of a class object use the create_instance method as follows: class_object.create_instanceproperties Syst em Administ rat ors Guide 34 8

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Replace class_object with the name of the class object and properties with a dictionary that consists of key-value pairs where keys represent instance properties and values represent property values. This method returns an LMIInstance object. Example 19 .16 . Creating New Instances The LMI_Group class represents system groups and the LMI_Account class represents user accounts on the managed system. To use the ns namespace object created in Example 19.5 “Accessing Namespace Objects” create instances of these two classes for the system group named pegasus and the user named lmishell-user and assign them to variables named group and user type the following at the interactive prompt: group ns.LMI_Group.first_instance"Name" : "pegasus" user ns.LMI_Account.first_instance"Name" : "lmishell-user" To get an instance of the LMI_Identity class for the lmishell-user user type: identity user.first_associatorResultClass"LMI_Identity" The LMI_MemberOfGroup class represents system group membership. To use the LMI_MemberOfGroup class to add the lmishell-user to the pegasus group create a new instance of this class as follows: ns.LMI_MemberOfGroup.create_instance ... "Member" : identity.path ... "Collection" : group.path LMIInstanceclassname"LMI_MemberOfGroup" ... Delet ing Individual Inst ances To delete a particular instance from the CIMOM use the delete method as follows: instance_object.delete Replace instance_object with the name of the instance object to delete. This method returns a boolean. Note that after deleting an instance its properties and methods become inaccessible. Example 19 .17. Deleting Individual Instances The LMI_Account class represents user accounts on the managed system. To use the ns namespace object created in Example 19.5 “Accessing Namespace Objects” create an instance of the LMI_Account class for the user named lmishell-user and assign it to a variable named user type the following at the interactive prompt: user ns.LMI_Account.first_instance"Name" : "lmishell-user" To delete this instance and remove the lmishell-user from the system type: ⁠Chapt er 1 9 . OpenLMI 34 9

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user.delete True List ing and Accessing Available Pro pert ies To list all available properties of a particular instance object use the print_properties method as follows: instance_object.print_properties Replace instance_object with the name of the instance object to inspect. This method prints available properties to standard output. To get a list of available properties use the properties method: instance_object.properties This method returns a list of strings. Example 19 .18. Listing Available Properties To inspect the device instance object created in Example 19.14 “Accessing Instances” and list all available properties type the following at the interactive prompt: device.print_properties RequestedState HealthState StatusDescriptions TransitioningToState Generation ... To assign a list of these properties to a variable named device_properties type: device_properties device.properties To get the current value of a particular property use the following syntax: instance_object.property_name Replace property_name with the name of the property to access. To modify the value of a particular property assign a value to it as follows: instance_object.property_name value Replace value with the new value of the property. Note that in order to propagate the change to the CIMOM you must also execute the push method: Syst em Administ rat ors Guide 350

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instance_object.push This method returns a three-item tuple consisting of a return value return value parameters and an error string. Example 19 .19 . Accessing Individual Properties To inspect the device instance object created in Example 19.14 “Accessing Instances” and display the value of the property named SystemName type the following at the interactive prompt: device.SystemName userver.example.com List ing and Using Available Met ho ds To list all available methods of a particular instance object use the print_methods method as follows: instance_object.print_methods Replace instance_object with the name of the instance object to inspect. This method prints available methods to standard output. To get a list of available methods use the method method: instance_object.methods This method returns a list of strings. Example 19 .20. Listing Available Methods To inspect the device instance object created in Example 19.14 “Accessing Instances” and list all available methods type the following at the interactive prompt: device.print_methods RequestStateChange To assign a list of these methods to a variable named network_device_methods type: network_device_methods device.methods To call a particular method use the following syntax: instance_object.method_name parametervalue ... ⁠Chapt er 1 9 . OpenLMI 351

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Replace instance_object with the name of the instance object to use method_name with the name of the method to call parameter with the name of the parameter to set and value with the value of this parameter. Methods return a three-item tuple consisting of a return value return value parameters and an error string. Important LMIInstance objects do not automatically refresh their contents properties methods qualifiers and so on. To do so use the refresh method as described below. Example 19 .21. Using Methods The PG_ComputerSystem class represents the system. To create an instance of this class by using the ns namespace object created in Example 19.5 “Accessing Namespace Objects” and assign it to a variable named sys type the following at the interactive prompt: sys ns.PG_ComputerSystem.first_instance The LMI_AccountManagementService class implements methods that allow you to manage users and groups in the system. To create an instance of this class and assign it to a variable named acc type: acc ns.LMI_AccountManagementService.first_instance To create a new user named lmishell-user in the system use the CreateAccount method as follows: acc.CreateAccountName"lmishell-user" Systemsys LMIReturnValuerval0 rparamsNocaseDictuAccount: LMIInstanceNameclassname"LMI_Account"... uIdentities: LMIInstanceNameclassname"LMI_Identity"... LMIInstanceNameclassname"LMI_Identity"... errorstr LMIShell support synchronous method calls: when you use a synchronous method LMIShell waits for the corresponding Job object to change its state to “finished” and then returns the return parameters of this job. LMIShell is able to perform a synchronous method call if the given method returns an object of one of the following classes: LMI_StorageJob LMI_SoftwareInstallationJob LMI_NetworkJob LMIShell first tries to use indications as the waiting method. If it fails it uses a polling method instead. To perform a synchronous method call use the following syntax: Syst em Administ rat ors Guide 352

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instance_object.Syncmethod_name parametervalue ... Replace instance_object with the name of the instance object to use method_name with the name of the method to call parameter with the name of the parameter to set and value with the value of this parameter. All synchronous methods have the Sync prefix in their name and return a three-item tuple consisting of the jobs return value jobs return value parameters and jobs error string. You can also force LMIShell to use only polling method. To do so specify the PreferPolling parameter as follows: instance_object.Syncmethod_name PreferPollingTrue parametervalue ... List ing and Viewing ValueMap Paramet ers CIM methods may contain ValueMap parameters in their Managed Object Format MOF definition. ValueMap parameters contain constant values. To list all available ValueMap parameters of a particular method use the print_valuemap_parameters method as follows: instance_object.method_name.print_valuemap_parameters Replace instance_object with the name of the instance object and method_name with the name of the method to inspect. This method prints available ValueMap parameters to standard output. To get a list of available ValueMap parameters use the valuemap_parameters method: instance_object.method_name.valuemap_parameters This method returns a list of strings. Example 19 .22. Listing ValueMap Parameters To inspect the acc instance object created in Example 19.21 “Using Methods” and list all available ValueMap parameters of the CreateAccount method type the following at the interactive prompt: acc.CreateAccount.print_valuemap_parameters CreateAccount To assign a list of these ValueMap parameters to a variable named create_account_parameters type: create_account_parameters acc.CreateAccount.valuemap_parameters ⁠Chapt er 1 9 . OpenLMI 353

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To access a particular ValueMap parameter use the following syntax: instance_object.method_name.valuemap_parameterValues Replace valuemap_parameter with the name of the ValueMap parameter to access. To list all available constant values use the print_values method as follows: instance_object.method_name.valuemap_parameterValues.print_values This method prints available named constant values to standard output. You can also get a list of available constant values by using the values method: instance_object.method_name.valuemap_parameterValues.values This method returns a list of strings. Example 19 .23. Accessing ValueMap Parameters Example 19.22 “Listing ValueMap Parameters” mentions a ValueMap parameter named CreateAccount. To inspect this parameter and list available constant values type the following at the interactive prompt: acc.CreateAccount.CreateAccountValues.print_values Operationunsupported Failed Unabletosetpasswordusercreated Unabletocreatehomedirectoryusercreatedandpasswordset Operationcompletedsuccessfully To assign a list of these constant values to a variable named create_account_values type: create_account_values acc.CreateAccount.CreateAccountValues.values To access a particular constant value use the following syntax: instance_object.method_name.valuemap_parameterValues.constant_value_name Replace constant_value_name with the name of the constant value. Alternatively you can use the value method as follows: instance_object.method_name.valuemap_parameterValues.value"constant_val ue_name" To determine the name of a particular constant value use the value_name method: instance_object.method_name.valuemap_parameterValues.value_name"constan t_value" Syst em Administ rat ors Guide 354

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This method returns a string. Example 19 .24 . Accessing Constant Values Example 19.23 “Accessing ValueMap Parameters” shows that the CreateAccount ValueMap parameter provides a constant value named Failed. To access this named constant value type the following at the interactive prompt: acc.CreateAccount.CreateAccountValues.Failed 2 acc.CreateAccount.CreateAccountValues.value"Failed" 2 To determine the name of this constant value type: acc.CreateAccount.CreateAccountValues.value_name2 uFailed Refreshing Inst ance Object s Local objects used by LMIShell which represent CIM objects at CIMOM side can get outdated if such objects change while working with LMIShells ones. To update the properties and methods of a particular instance object use the refresh method as follows: instance_object.refresh Replace instance_object with the name of the object to refresh. This method returns a three-item tuple consisting of a return value return value parameter and an error string. Example 19 .25. Refreshing Instance Objects To update the properties and methods of the device instance object created in Example 19.14 “Accessing Instances” type the following at the interactive prompt: device.refresh LMIReturnValuervalTrue rparamsNocaseDict errorstr Displaying MOF Represent at io n To display the Managed Object Format MOF representation of an instance object use the tomof method as follows: instance_object.tomof Replace instance_object with the name of the instance object to inspect. This method prints the MOF representation of the object to standard output. ⁠Chapt er 1 9 . OpenLMI 355

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Example 19 .26 . Displaying MOF Representation To display the MOF representation of the device instance object created in Example 19.14 “Accessing Instances” type the following at the interactive prompt: device.tomof instance of LMI_IPNetworkConnection RequestedState 12 HealthState NULL StatusDescriptions NULL TransitioningToState 12 ... 19.4 .6. Working with Instance Names LMIShell instance names are objects that hold a set of primary keys and their values. This type of an object exactly identifies an instance. Accessing Inst ance Names CIMInstance objects are identified by CIMInstanceName objects. To get a list of all available instance name objects use the instance_names method as follows: class_object.instance_names Replace class_object with the name of the class object to inspect. This method returns a list of LMIInstanceName objects. To access the first instance name object of a class object use the first_instance_name method: class_object.first_instance_name This method returns an LMIInstanceName object. In addition to listing all instance name objects or returning the first one both instance_names and first_instance_name support an optional argument to allow you to filter the results: class_object.instance_namescriteria class_object.first_instance_namecriteria Replace criteria with a dictionary consisting of key-value pairs where keys represent key properties and values represent required values of these key properties. Example 19 .27. Accessing Instance Names To find the first instance name of the cls class object created in Example 19.7 “Accessing Class Objects” that has the Name key property equal to eth0 and assign it to a variable named device_name type the following at the interactive prompt: Syst em Administ rat ors Guide 356

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device_name cls.first_instance_name"Name": "eth0" Examining Inst ance Names All instance name objects store information about their class name and the namespace they belong to. To get the class name of a particular instance name object use the following syntax: instance_name_object.classname Replace instance_name_object with the name of the instance name object to inspect. This returns a string representation of the class name. To get information about the namespace an instance name object belongs to use: instance_name_object.namespace This returns a string representation of the namespace. Example 19 .28. Examining Instance Names To inspect the device_name instance name object created in Example 19.27 “Accessing Instance Names” and display its class name and the corresponding namespace type the following at the interactive prompt: device_name.classname uLMI_IPNetworkConnection device_name.namespace root/cimv2 Creat ing New Inst ance Names LMIShell allows you to create a new wrapped CIMInstanceName object if you know all primary keys of a remote object. This instance name object can then be used to retrieve the whole instance object. To create a new instance name of a class object use the new_instance_name method as follows: class_object.new_instance_namekey_properties Replace class_object with the name of the class object and key_properties with a dictionary that consists of key-value pairs where keys represent key properties and values represent key property values. This method returns an LMIInstanceName object. Example 19 .29 . Creating New Instance Names ⁠Chapt er 1 9 . OpenLMI 357

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The LMI_Account class represents user accounts on the managed system. To use the ns namespace object created in Example 19.5 “Accessing Namespace Objects” and create a new instance name of the LMI_Account class representing the lmishell-user user on the managed system type the following at the interactive prompt: instance_name ns.LMI_Account.new_instance_name ... "CreationClassName" : "LMI_Account" ... "Name" : "lmishell-user" ... "SystemCreationClassName" : "PG_ComputerSystem" ... "SystemName" : "server" List ing and Accessing Key Pro pert ies To list all available key properties of a particular instance name object use the print_key_properties method as follows: instance_name_object.print_key_properties Replace instance_name_object with the name of the instance name object to inspect. This method prints available key properties to standard output. To get a list of available key properties use the key_properties method: instance_name_object.key_properties This method returns a list of strings. Example 19 .30. Listing Available Key Properties To inspect the device_name instance name object created in Example 19.27 “Accessing Instance Names” and list all available key properties type the following at the interactive prompt: device_name.print_key_properties CreationClassName SystemName Name SystemCreationClassName To assign a list of these key properties to a variable named device_name_properties type: device_name_properties device_name.key_properties To get the current value of a particular key property use the following syntax: instance_name_object.key_property_name Replace key_property_name with the name of the key property to access. Syst em Administ rat ors Guide 358

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Example 19 .31. Accessing Individual Key Properties To inspect the device_name instance name object created in Example 19.27 “Accessing Instance Names” and display the value of the key property named SystemName type the following at the interactive prompt: device_name.SystemName userver.example.com Co nvert ing Inst ance Names t o Inst ances Each instance name can be converted to an instance. To do so use the to_instance method as follows: instance_name_object.to_instance Replace instance_name_object with the name of the instance name object to convert. This method returns an LMIInstance object. Example 19 .32. Converting Instance Names to Instances To convert the device_name instance name object created in Example 19.27 “Accessing Instance Names” to an instance object and assign it to a variable named device type the following at the interactive prompt: device device_name.to_instance 19.4 .7. Working with Associated Objects The Common Information Model defines an association relationship between managed objects. Accessing Asso ciat ed Inst ances To get a list of all objects associated with a particular instance object use the associators method as follows: instance_object.associators AssocClassclass_name ResultClassclass_name ResultRolerole IncludeQualifiersinclude_qualifiers IncludeClassOrigininclude_class_origin PropertyListproperty_list To access the first object associated with a particular instance object use the first_associator method: instance_object.first_associator AssocClassclass_name ⁠Chapt er 1 9 . OpenLMI 359

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ResultClassclass_name ResultRolerole IncludeQualifiersinclude_qualifiers IncludeClassOrigininclude_class_origin PropertyListproperty_list Replace instance_object with the name of the instance object to inspect. You can filter the results by specifying the following parameters: AssocClass — Each returned object must be associated with the source object through an instance of this class or one of its subclasses. The default value is None. ResultClass — Each returned object must be either an instance of this class or one of its subclasses or it must be this class or one of its subclasses. The default value is None. Role — Each returned object must be associated with the source object through an association in which the source object plays the specified role. The name of the property in the association class that refers to the source object must match the value of this parameter. The default value is None. ResultRole — Each returned object must be associated with the source object through an association in which the returned object plays the specified role. The name of the property in the association class that refers to the returned object must match the value of this parameter. The default value is None. The remaining parameters refer to: IncludeQualifiers — A boolean indicating whether all qualifiers of each object including qualifiers on the object and on any returned properties should be included as QUALIFIER elements in the response. The default value is False. IncludeClassOrigin — A boolean indicating whether the CLASSORIGIN attribute should be present on all appropriate elements in each returned object. The default value is False. PropertyList — The members of this list define one or more property names. Returned objects will not include elements for any properties missing from this list. If PropertyList is an empty list no properties are included in returned objects. If it is None no additional filtering is defined. The default value is None. Example 19 .33. Accessing Associated Instances The LMI_StorageExtent class represents block devices available in the system. To use the ns namespace object created in Example 19.5 “Accessing Namespace Objects” create an instance of the LMI_StorageExtent class for the block device named /dev/vda and assign it to a variable named vda type the following at the interactive prompt: vda ns.LMI_StorageExtent.first_instance ... "DeviceID" : "/dev/vda" To get a list of all disk partitions on this block device and assign it to a variable named vda_partitions use the associators method as follows: vda_partitions vda.associatorsResultClass"LMI_DiskPartition" Syst em Administ rat ors Guide 360

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Accessing Asso ciat ed Inst ance Names To get a list of all associated instance names of a particular instance object use the associator_names method as follows: instance_object.associator_names AssocClassclass_name ResultClassclass_name Rolerole ResultRolerole To access the first associated instance name of a particular instance object use the first_associator_name method: instance_object.first_associator_name AssocClassclass_object ResultClassclass_object Rolerole ResultRolerole Replace instance_object with the name of the instance object to inspect. You can filter the results by specifying the following parameters: AssocClass — Each returned name identifies an object that must be associated with the source object through an instance of this class or one of its subclasses. The default value is None. ResultClass — Each returned name identifies an object that must be either an instance of this class or one of its subclasses or it must be this class or one of its subclasses. The default value is None. Role — Each returned name identifies an object that must be associated with the source object through an association in which the source object plays the specified role. The name of the property in the association class that refers to the source object must match the value of this parameter. The default value is None. ResultRole — Each returned name identifies an object that must be associated with the source object through an association in which the returned named object plays the specified role. The name of the property in the association class that refers to the returned object must match the value of this parameter. The default value is None. Example 19 .34 . Accessing Associated Instance Names To use the vda instance object created in Example 19.33 “Accessing Associated Instances” get a list of its associated instance names and assign it to a variable named vda_partitions type: vda_partitions vda.associator_namesResultClass"LMI_DiskPartition" 19.4 .8. Working with Association Objects The Common Information Model defines an association relationship between managed objects. Association objects define the relationship between two other objects. ⁠Chapt er 1 9 . OpenLMI 361

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Accessing Asso ciat io n Inst ances To get a list of association objects that refer to a particular target object use the references method as follows: instance_object.references ResultClassclass_name Rolerole IncludeQualifiersinclude_qualifiers IncludeClassOrigininclude_class_origin PropertyListproperty_list To access the first association object that refers to a particular target object use the first_reference method: instance_object.first_reference ... ResultClassclass_name ... Rolerole ... IncludeQualifiersinclude_qualifiers ... IncludeClassOrigininclude_class_origin ... PropertyListproperty_list Replace instance_object with the name of the instance object to inspect. You can filter the results by specifying the following parameters: ResultClass — Each returned object must be either an instance of this class or one of its subclasses or it must be this class or one of its subclasses. The default value is None. Role — Each returned object must refer to the target object through a property with a name that matches the value of this parameter. The default value is None. The remaining parameters refer to: IncludeQualifiers — A boolean indicating whether each object including qualifiers on the object and on any returned properties should be included as a QUALIFIER element in the response. The default value is False. IncludeClassOrigin — A boolean indicating whether the CLASSORIGIN attribute should be present on all appropriate elements in each returned object. The default value is False. PropertyList — The members of this list define one or more property names. Returned objects will not include elements for any properties missing from this list. If PropertyList is an empty list no properties are included in returned objects. If it is None no additional filtering is defined. The default value is None. Example 19 .35. Accessing Association Instances The LMI_LANEndpoint class represents a communication endpoint associated with a certain network interface device. To use the ns namespace object created in Example 19.5 “Accessing Namespace Objects” create an instance of the LMI_LANEndpoint class for the network interface device named eth0 and assign it to a variable named lan_endpoint type the following at the interactive prompt: Syst em Administ rat ors Guide 362

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lan_endpoint ns.LMI_LANEndpoint.first_instance ... "Name" : "eth0" To access the first association object that refers to an LMI_BindsToLANEndpoint object and assign it to a variable named bind type: bind lan_endpoint.first_reference ... ResultClass"LMI_BindsToLANEndpoint" You can now use the Dependent property to access the dependent LMI_IPProtocolEndpoint class that represents the IP address of the corresponding network interface device: ip bind.Dependent.to_instance print ip.IPv4Address 192.168.122.1 Accessing Asso ciat io n Inst ance Names To get a list of association instance names of a particular instance object use the reference_names method as follows: instance_object.reference_names ResultClassclass_name Rolerole To access the first association instance name of a particular instance object use the first_reference_name method: instance_object.first_reference_name ResultClassclass_name Rolerole Replace instance_object with the name of the instance object to inspect. You can filter the results by specifying the following parameters: ResultClass — Each returned object name identifies either an instance of this class or one of its subclasses or this class or one of its subclasses. The default value is None. Role — Each returned object identifies an object that refers to the target instance through a property with a name that matches the value of this parameter. The default value is None. Example 19 .36 . Accessing Association Instance Names To use the lan_endpoint instance object created in Example 19.35 “Accessing Association Instances” access the first association instance name that refers to an LMI_BindsToLANEndpoint object and assign it to a variable named bind type: ⁠Chapt er 1 9 . OpenLMI 363

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bind lan_endpoint.first_reference_name ... ResultClass"LMI_BindsToLANEndpoint" You can now use the Dependent property to access the dependent LMI_IPProtocolEndpoint class that represents the IP address of the corresponding network interface device: ip bind.Dependent.to_instance print ip.IPv4Address 192.168.122.1 19.4 .9. Working with Indications Indication is a reaction to a specific event that occurs in response to a particular change in data. LMIShell can subscribe to an indication in order to receive such event responses. Subscribing t o Indicat io ns To subscribe to an indication use the subscribe_indication method as follows: connection_object.subscribe_indication QueryLanguage"WQL" QuerySELECT FROM CIM_InstModification Name"cpu" CreationNamespace"root/interop" SubscriptionCreationClassName"CIM_IndicationSubscription" FilterCreationClassName"CIM_IndicationFilter" FilterSystemCreationClassName"CIM_ComputerSystem" FilterSourceNamespace"root/cimv2" HandlerCreationClassName"CIM_IndicationHandlerCIMXML" HandlerSystemCreationClassName"CIM_ComputerSystem" Destination"http://host_name:5988" Alternatively you can use a shorter version of the method call as follows: connection_object.subscribe_indication QuerySELECT FROM CIM_InstModification Name"cpu" Destination"http://host_name:5988" Replace connection_object with a connection object and host_name with the host name of the system you want to deliver the indications to. By default all subscriptions created by the LMIShell interpreter are automatically deleted when the interpreter terminates. To change this behavior pass the PermanentTrue keyword parameter to the subscribe_indication method call. This will prevent LMIShell from deleting the subscription. Example 19 .37. Subscribing to Indications Syst em Administ rat ors Guide 364

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To use the c connection object created in Example 19.1 “Connecting to a Remote CIMOM” and subscribe to an indication named cpu type the following at the interactive prompt: c.subscribe_indication ... QueryLanguage"WQL" ... QuerySELECT FROM CIM_InstModification ... Name"cpu" ... CreationNamespace"root/interop" ... SubscriptionCreationClassName"CIM_IndicationSubscription" ... FilterCreationClassName"CIM_IndicationFilter" ... FilterSystemCreationClassName"CIM_ComputerSystem" ... FilterSourceNamespace"root/cimv2" ... HandlerCreationClassName"CIM_IndicationHandlerCIMXML" ... HandlerSystemCreationClassName"CIM_ComputerSystem" ... Destination"http://server.example.com:5988" LMIReturnValuervalTrue rparamsNocaseDict errorstr List ing Subscribed Indicat io ns To list all the subscribed indications use the print_subscribed_indications method as follows: connection_object.print_subscribed_indications Replace connection_object with the name of the connection object to inspect. This method prints subscribed indications to standard output. To get a list of subscribed indications use the subscribed_indications method: connection_object.subscribed_indications This method returns a list of strings. Example 19 .38. Listing Subscribed Indications To inspect the c connection object created in Example 19.1 “Connecting to a Remote CIMOM” and list all subscribed indications type the following at the interactive prompt: c.print_subscribed_indications To assign a list of these indications to a variable named indications type: indications c.subscribed_indications Unsubscribing fro m Indicat io ns ⁠Chapt er 1 9 . OpenLMI 365

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By default all subscriptions created by the LMIShell interpreter are automatically deleted when the interpreter terminates. To delete an individual subscription sooner use the unsubscribe_indication method as follows: connection_object.unsubscribe_indicationindication_name Replace connection_object with the name of the connection object and indication_name with the name of the indication to delete. To delete all subscriptions use the unsubscribe_all_indications method: connection_object.unsubscribe_all_indications Example 19 .39 . Unsubscribing from Indications To use the c connection object created in Example 19.1 “Connecting to a Remote CIMOM” and unsubscribe from the indication created in Example 19.37 “Subscribing to Indications” type the following at the interactive prompt: c.unsubscribe_indicationcpu LMIReturnValuervalTrue rparamsNocaseDict errorstr Implement ing an Indicat io n Handler The subscribe_indication method allows you to specify the host name of the system you want to deliver the indications to. The following example shows how to implement an indication handler: def handlerind arg1 arg2 kwargs: ... exported_objects ind.exported_objects ... do_something_withexported_objects listener LmiIndicationListener"0.0.0.0" listening_port listener.add_handler"indication-name-XXXXXXXX" handler arg1 arg2 kwargs listener.start The first argument of the handler is an LmiIndication object which contains a list of methods and objects exported by the indication. Other parameters are user specific: those arguments need to be specified when adding a handler to the listener. In the example above the add_handler method call uses a special string with eight “X” characters. These characters are replaced with a random string that is generated by listeners in order to avoid a possible handler name collision. To use the random string start the indication listener first and then subscribe to an indication so that the Destination property of the handler object contains the following value: schema://host_name/random_string. Example 19 .4 0. Implementing an Indication Handler Syst em Administ rat ors Guide 366

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The following script illustrates how to write a handler that monitors a managed system located at 192.168.122.1 and calls the indication_callback function whenever a new user account is created: /usr/bin/lmishell import sys from time import sleep from lmi.shell.LMIUtil import LMIPassByRef from lmi.shell.LMIIndicationListener import LMIIndicationListener These are passed by reference to indication_callback var1 LMIPassByRef"some_value" var2 LMIPassByRef"some_other_value" def indication_callbackind var1 var2: Do something with ind var1 and var2 print ind.exported_objects print var1.value print var2.value c connect"hostname" "username" "password" listener LMIIndicationListener"0.0.0.0" 65500 unique_name listener.add_handler "demo-XXXXXXXX" Creates a unique name for me indication_callback Callback to be called var1 Variable passed by ref var2 Variable passed by ref listener.start print c.subscribe_indication Nameunique_name Query"SELECT FROM LMI_AccountInstanceCreationIndication WHERE SOURCEINSTANCE ISA LMI_Account" Destination"192.168.122.1:65500" try: while True: sleep60 except KeyboardInterrupt: sys.exit0 19.4 .10. Example Usage This section provides a number of examples for various CIM providers distributed with the OpenLMI packages. All examples in this section use the following two variable definitions: c connect"host_name" "user_name" "password" ns c.root.cimv2 ⁠Chapt er 1 9 . OpenLMI 367

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Replace host_name with the host name of the managed system user_name with the name of user that is allowed to connect to OpenPegasus CIMOM running on that system and password with the users password. Using t he OpenLMI Service Pro vider The openlmi-service package installs a CIM provider for managing system services. The examples below illustrate how to use this CIM provider to list available system services and how to start stop enable and disable them. Example 19 .4 1. Listing Available Services To list all available services on the managed machine along with information regarding whether the service has been started TRUE or stopped FALSE and the status string use the following code snippet: for service in ns.LMI_Service.instances: print "s:\ts" service.Name service.Status To list only the services that are enabled by default use this code snippet: cls ns.LMI_Service for service in cls.instances: if service.EnabledDefault cls.EnabledDefaultValues.Enabled: print service.Name Note that the value of the EnabledDefault property is equal to 2 for enabled services and 3 for disabled services. To display information about the cups service use the following: cups ns.LMI_Service.first_instance"Name": "cups.service" cups.doc Example 19 .4 2. Starting and Stopping Services To start and stop the cups service and to see its current status use the following code snippet: cups ns.LMI_Service.first_instance"Name": "cups.service" cups.StartService print cups.Status cups.StopService print cups.Status Example 19 .4 3. Enabling and Disabling Services To enable and disable the cups service and to display its EnabledDefault property use the following code snippet: cups ns.LMI_Service.first_instance"Name": "cups.service" cups.TurnServiceOff Syst em Administ rat ors Guide 368

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print cups.EnabledDefault cups.TurnServiceOn print cups.EnabledDefault Using t he OpenLMI Net wo rking Pro vider The openlmi-networking package installs a CIM provider for networking. The examples below illustrate how to use this CIM provider to list IP addresses associated with a certain port number create a new connection configure a static IP address and activate a connection. Example 19 .4 4 . Listing IP Addresses Associated with a Given Port Number To list all IP addresses associated with the eth0 network interface use the following code snippet: device ns.LMI_IPNetworkConnection.first_instanceElementName: eth0 for endpoint in device.associatorsAssocClass"LMI_NetworkSAPSAPDependency" ResultClass"LMI_IPProtocolEndpoint": if endpoint.ProtocolIFType ns.LMI_IPProtocolEndpoint.ProtocolIFTypeValues.IPv4: print "IPv4: s/s" endpoint.IPv4Address endpoint.SubnetMask elif endpoint.ProtocolIFType ns.LMI_IPProtocolEndpoint.ProtocolIFTypeValues.IPv6: print "IPv6: s/d" endpoint.IPv6Address endpoint.IPv6SubnetPrefixLength This code snippet uses the LMI_IPProtocolEndpoint class associated with a given LMI_IPNetworkConnection class. To display the default gateway use this code snippet: for rsap in device.associatorsAssocClass"LMI_NetworkRemoteAccessAvailableToElement " ResultClass"LMI_NetworkRemoteServiceAccessPoint": if rsap.AccessContext ns.LMI_NetworkRemoteServiceAccessPoint.AccessContextValues.DefaultGatew ay: print "Default Gateway: s" rsap.AccessInfo The default gateway is represented by an LMI_NetworkRemoteServiceAccessPoint instance with the AccessContext property equal to DefaultGateway. To get a list of DNS servers the object model needs to be traversed as follows: 1. Get the LMI_IPProtocolEndpoint instances associated with a given LMI_IPNetworkConnection using LMI_NetworkSAPSAPDependency. 2. Use the same association for the LMI_DNSProtocolEndpoint instances. ⁠Chapt er 1 9 . OpenLMI 369

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The LMI_NetworkRemoteServiceAccessPoint instances with the AccessContext property equal to the DNS Server associated through LMI_NetworkRemoteAccessAvailableToElement have the DNS server address in the AccessInfo property. There can be more possible paths to get to the RemoteServiceAccessPath and entries can be duplicated. The following code snippet uses the set function to remove duplicate entries from the list of DNS servers: dnsservers set for ipendpoint in device.associatorsAssocClass"LMI_NetworkSAPSAPDependency" ResultClass"LMI_IPProtocolEndpoint": for dnsedpoint in ipendpoint.associatorsAssocClass"LMI_NetworkSAPSAPDependency" ResultClass"LMI_DNSProtocolEndpoint": for rsap in dnsedpoint.associatorsAssocClass"LMI_NetworkRemoteAccessAvailableToEle ment" ResultClass"LMI_NetworkRemoteServiceAccessPoint": if rsap.AccessContext ns.LMI_NetworkRemoteServiceAccessPoint.AccessContextValues.DNSServer: dnsservers.addrsap.AccessInfo print "DNS:" " ".joindnsservers Example 19 .4 5. Creating a New Connection and Configuring a Static IP Address To create a new setting with a static IPv4 and stateless IPv6 configuration for network interface eth0 use the following code snippet: capability ns.LMI_IPNetworkConnectionCapabilities.first_instance ElementName: eth0 result capability.LMI_CreateIPSettingCaptioneth0 Static IPv4Typecapability.LMI_CreateIPSetting.IPv4TypeValues.Static IPv6Typecapability.LMI_CreateIPSetting.IPv6TypeValues.Stateless setting result.rparams"SettingData".to_instance for settingData in setting.associatorsAssocClass"LMI_OrderedIPAssignmentComponent": if setting.ProtocolIFType ns.LMI_IPAssignmentSettingData.ProtocolIFTypeValues.IPv4: Set static IPv4 address settingData.IPAddresses "192.168.1.100" settingData.SubnetMasks "255.255.0.0" settingData.GatewayAddresses "192.168.1.1" settingData.push This code snippet creates a new setting by calling the LMI_CreateIPSetting method on the instance of LMI_IPNetworkConnectionCapabilities which is associated with LMI_IPNetworkConnection through LMI_IPNetworkConnectionElementCapabilities. It also uses the push method to modify the setting. Example 19 .4 6 . Activating a Connection Syst em Administ rat ors Guide 370

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To apply a setting to the network interface call the ApplySettingToIPNetworkConnection method of the LMI_IPConfigurationService class. This method is asynchronous and returns a job. The following code snippets illustrates how to call this method synchronously: setting ns.LMI_IPAssignmentSettingData.first_instance "Caption": "eth0 Static" port ns.LMI_IPNetworkConnection.first_instance ElementName: ens8 service ns.LMI_IPConfigurationService.first_instance service.SyncApplySettingToIPNetworkConnectionSettingDatasetting IPNetworkConnectionport Mode32768 The Mode parameter affects how the setting is applied. The most commonly used values of this parameter are as follows: 1 — apply the setting now and make it auto-activated. 2 — make the setting auto-activated and do not apply it now. 4 — disconnect and disable auto-activation. 5 — do not change the setting state only disable auto-activation. 32768 — apply the setting. 32769 — disconnect. Using t he OpenLMI St o rage Pro vider The openlmi-storage package installs a CIM provider for storage management. The examples below illustrate how to use this CIM provider to create a volume group create a logical volume build a file system mount a file system and list block devices known to the system. In addition to the c and ns variables these examples use the following variable definitions: MEGABYTE 10241024 storage_service ns.LMI_StorageConfigurationService.first_instance filesystem_service ns.LMI_FileSystemConfigurationService.first_instance Example 19 .4 7. Creating a Volume Group To create a new volume group located in /dev/myGroup/ that has three members and the default extent size of 4 MB use the following code snippet: Find the devices to add to the volume group filtering the CIM_StorageExtent.instances call would be faster but this is easier to read: sda1 ns.CIM_StorageExtent.first_instance"Name": "/dev/sda1" sdb1 ns.CIM_StorageExtent.first_instance"Name": "/dev/sdb1" sdc1 ns.CIM_StorageExtent.first_instance"Name": "/dev/sdc1" Create a new volume group: ret outparams err storage_service.SyncCreateOrModifyVG ElementName"myGroup" ⁠Chapt er 1 9 . OpenLMI 371

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InExtentssda1 sdb1 sdc1 vg outparamsPool.to_instance print "VG" vg.PoolID \ "with extent size" vg.ExtentSize \ "and" vg.RemainingExtents "free extents created." Example 19 .4 8. Creating a Logical Volume To create two logical volumes with the size of 100 MB use this code snippet: Find the volume group: vg ns.LMI_VGStoragePool.first_instance"Name": "/dev/mapper/myGroup" Create the first logical volume: ret outparams err storage_service.SyncCreateOrModifyLV ElementName"Vol1" InPoolvg Size100 MEGABYTE lv outparamsTheElement.to_instance print "LV" lv.DeviceID \ "with" lv.BlockSize lv.NumberOfBlocks\ "bytes created." Create the second logical volume: ret outparams err storage_service.SyncCreateOrModifyLV ElementName"Vol2" InPoolvg Size100 MEGABYTE lv outparamsTheElement.to_instance print "LV" lv.DeviceID \ "with" lv.BlockSize lv.NumberOfBlocks \ "bytes created." Example 19 .4 9 . Creating a File System To create an ext3 file system on logical volume lv from Example 19.48 “Creating a Logical Volume” use the following code snippet: ret outparams err filesystem_service.SyncLMI_CreateFileSystem FileSystemTypefilesystem_service.LMI_CreateFileSystem.FileSystemTypeVa lues.EXT3 InExtentslv Example 19 .50. Mounting a File System To mount the file system created in Example 19.49 “Creating a File System” use the following code snippet: Find the file system on the logical volume: fs lv.first_associatorResultClass"LMI_LocalFileSystem" Syst em Administ rat ors Guide 372

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mount_service ns.LMI_MountConfigurationService.first_instance rc out err mount_service.SyncCreateMount FileSystemTypeext3 Mode32768 just mount FileSystemfs MountPoint/mnt/test FileSystemSpeclv.Name Example 19 .51. Listing Block Devices To list all block devices known to the system use the following code snippet: devices ns.CIM_StorageExtent.instances for device in devices: if lmi_isinstancedevice ns.CIM_Memory: Memory and CPU caches are StorageExtents too do not print them continue print device.classname print device.DeviceID print device.Name print device.BlockSizedevice.NumberOfBlocks Using t he OpenLMI Hardware Pro vider The openlmi-hardware package installs a CIM provider for monitoring hardware. The examples below illustrate how to use this CIM provider to retrieve information about CPU memory modules PCI devices and the manufacturer and model of the machine. Example 19 .52. Viewing CPU Information To display basic CPU information such as the CPU name the number of processor cores and the number of hardware threads use the following code snippet: cpu ns.LMI_Processor.first_instance cpu_cap cpu.associatorsResultClass"LMI_ProcessorCapabilities"0 print cpu.Name print cpu_cap.NumberOfProcessorCores print cpu_cap.NumberOfHardwareThreads Example 19 .53. Viewing Memory Information To display basic information about memory modules such as their individual sizes use the following code snippet: mem ns.LMI_Memory.first_instance for i in mem.associatorsResultClass"LMI_PhysicalMemory": print i.Name ⁠Chapt er 1 9 . OpenLMI 373

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Example 19 .54 . Viewing Chassis Information To display basic information about the machine such as its manufacturer or its model use the following code snippet: chassis ns.LMI_Chassis.first_instance print chassis.Manufacturer print chassis.Model Example 19 .55. Listing PCI Devices To list all PCI devices known to the system use the following code snippet: for pci in ns.LMI_PCIDevice.instances: print pci.Name 19.5. Using OpenLMI Scripts The LMIShell interpreter is built on top of Python modules that can be used to develop custom management tools. The OpenLMI Scripts project provides a number of Python libraries for interfacing with OpenLMI providers. In addition it is distributed with lmi an extensible utility that can be used to interact with these libraries from the command line. To install OpenLMI Scripts on your system type the following at a shell prompt: easy_install --user openlmi-scripts This command installs the Python modules and the lmi utility in the /.local/ directory. To extend the functionality of the lmi utility install additional OpenLMI modules by using the following command: easy_install --user package_name For a complete list of available modules see the Python website. For more information about OpenLMI Scripts see the official OpenLMI Scripts documentation. 19.6. Additional Resources For more information about OpenLMI and system management in general see the resources listed below. Installed Documentation lmishell1 — The manual page for the lmishell client and interpreter provides detailed information about its execution and usage. Online Documentation Syst em Administ rat ors Guide 374

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Red Hat Enterprise Linux 7 Networking Guide — The Networking Guide for Red Hat Enterprise Linux 7 documents relevant information regarding the configuration and administration of network interfaces and network services on the system. Red Hat Enterprise Linux 7 Storage Administration Guide — The Storage Administration Guide for Red Hat Enterprise Linux 7 provides instructions on how to manage storage devices and file systems on the system. Red Hat Enterprise Linux 7 Power Management Guide — The Power Management Guide for Red Hat Enterprise Linux 7 explains how to manage power consumption of the system effectively. It discusses different techniques that lower power consumption for both servers and laptops and explains how each technique affects the overall performance of the system. Red Hat Enterprise Linux 7 Linux Domain Identity Authentication and Policy Guide — The Linux Domain Identity Authentication and Policy Guide for Red Hat Enterprise Linux 7 covers all aspects of installing configuring and managing IPA domains including both servers and clients. The guide is intended for IT and systems administrators. FreeIPA Documentation — The FreeIPA Documentation serves as the primary user documentation for using the FreeIPA Identity Management project. OpenSSL Home Page — The OpenSSL home page provides an overview of the OpenSSL project. Mozilla NSS Documentation — The Mozilla NSS Documentation serves as the primary user documentation for using the Mozilla NSS project. See Also Chapter 3 Managing Users and Groups documents how to manage system users and groups in the graphical user interface and on the command line. Chapter 8 Yum describes how to use the Yum package manager to search install update and uninstall packages on the command line. Chapter 9 Managing Services with systemd provides an introduction to systemd and documents how to use the systemctl command to manage system services configure systemd targets and execute power management commands. Chapter 10 OpenSSH describes how to configure an SSH server and how to use the ssh scp and sftp client utilities to access it. ⁠Chapt er 1 9 . OpenLMI 375

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Chapter 20. Viewing and Managing Log Files Log files are files that contain messages about the system including the kernel services and applications running on it. There are different log files for different information. For example there is a default system log file a log file just for security messages and a log file for cron tasks. Log files can be very useful when trying to troubleshoot a problem with the system such as trying to load a kernel driver or when looking for unauthorized login attempts to the system. This chapter discusses where to find log files how to view log files and what to look for in log files. Some log files are controlled by a daemon called rsyslogd. The rsyslogd daemon is an enhanced replacement for sysklogd and provides extended filtering encryption protected relaying of messages various configuration options input and output modules support for transportation via the TCP or UDP protocols. Note that rsyslog is compatible with sysklogd. Log files can also be managed by the journald daemon – a component of systemd. The journald daemon captures Syslog messages kernel log messages initial RAM disk and early boot messages as well as messages written to standard output and standard error output of all services indexes them and makes this available to the user. The native journal file format which is a structured and indexed binary file improves searching and provides faster operation and it also stores meta data information like time stamps or user IDs. Log files produced by journald are by default not persistent log files are stored only in memory or a small ring-buffer in the /run/log/journal/ directory. The amount of logged data depends on free memory when you reach the capacity limit the oldest entries are deleted. However this setting can be altered – see Section 20.10.5 “Enabling Persistent Storage”. For more information on Journal see Section 20.10 “Using the Journal”. By default these two logging tools coexist on your system. The journald daemon is the primary tool for troubleshooting. It also provides additional data necessary for creating structured log messages. Data acquired by journald is forwarded into the /run/systemd/journal/syslog socket that may be used by rsyslogd to process the data further. However rsyslog does the actual integration by default via the imjournal input module thus avoiding the aforementioned socket. You can also transfer data in the opposite direction from rsyslogd to journald with use of omjournal module. See Section 20.7 “Interaction of Rsyslog and Journal” for further information. The integration enables maintaining text-based logs in a consistent format to ensure compatibility with possible applications or configurations dependent on rsyslogd. Also you can maintain rsyslog messages in a structured format see Section 20.8 “Structured Logging with Rsyslog”. 20.1. Locating Log Files A list of log files maintained by rsyslogd can be found in the /etc/rsyslog.conf configuration file. Most log files are located in the /var/log/ directory. Some applications such as httpd and samba have a directory within /var/log/ for their log files. You may notice multiple files in the /var/log/ directory with numbers after them for example cron-20100906. These numbers represent a time stamp that has been added to a rotated log file. Log files are rotated so their file sizes do not become too large. The logrotate package contains a cron task that automatically rotates log files according to the /etc/logrotate.conf configuration file and the configuration files in the /etc/logrotate.d/ directory. 20.2. Basic Configuration of Rsyslog The main configuration file for rsyslog is /etc/rsyslog.conf. Here you can specify global directives modules and rules that consist of filter and action parts. Also you can add comments in the Syst em Administ rat ors Guide 376

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form of text following a hash sign . 20.2.1. Filters A rule is specified by a filter part which selects a subset of syslog messages and an action part which specifies what to do with the selected messages. To define a rule in your /etc/rsyslog.conf configuration file define both a filter and an action on one line and separate them with one or more spaces or tabs. rsyslog offers various ways to filter syslog messages according to selected properties. The available filtering methods can be divided into Facility/Priority-based Property-based and Expression- based filters. Facility/Priority-based filters The most used and well-known way to filter syslog messages is to use the facility/priority- based filters which filter syslog messages based on two conditions: facility and priority separated by a dot. To create a selector use the following syntax: FACILITY.PRIORITY where: FACILITY specifies the subsystem that produces a specific syslog message. For example the mail subsystem handles all mail-related syslog messages. FACILITY can be represented by one of the following keywords or by a numerical code: kern 0 user 1 mail 2 daemon 3 auth 4 syslog 5 lpr 6 news 7 uucp 8 cron 9 authpriv 10 ftp 11 and local0 through local7 16 - 23. PRIORITY specifies a priority of a syslog message. PRIORITY can be represented by one of the following keywords or by a number: debug 7 info 6 notice 5 warning 4 err 3 crit 2 alert 1 and emerg 0. The aforementioned syntax selects syslog messages with the defined or higher priority. By preceding any priority keyword with an equal sign you specify that only syslog messages with the specified priority will be selected. All other priorities will be ignored. Conversely preceding a priority keyword with an exclamation mark selects all syslog messages except those with the defined priority. In addition to the keywords specified above you may also use an asterisk to define all facilities or priorities depending on where you place the asterisk before or after the comma. Specifying the priority keyword none serves for facilities with no given priorities. Both facility and priority conditions are case-insensitive. To define multiple facilities and priorities separate them with a comma . To define multiple selectors on one line separate them with a semi-colon . Note that each selector in the selector field is capable of overwriting the preceding ones which can exclude some priorities from the pattern. Example 20.1. Facility/Priority-based Filters The following are a few examples of simple facility/priority-based filters that can be specified in /etc/rsyslog.conf. To select all kernel syslog messages with any priority add the following text into the configuration file: kern. ⁠Chapt er 2 0 . Viewing and Managing Log Files 377

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To select all mail syslog messages with priority crit and higher use this form: mail.crit To select all cron syslog messages except those with the info or debug priority set the configuration in the following form: cron.infodebug Property-based filters Property-based filters let you filter syslog messages by any property such as timegenerated or syslogtag. For more information on properties see Section 20.2.3 “Properties”. You can compare each of the specified properties to a particular value using one of the compare-operations listed in Table 20.1 “Property-based compare-operations”. Both property names and compare operations are case-sensitive. Property-based filter must start with a colon :. To define the filter use the following syntax: :PROPERTY COMPARE_OPERATION "STRING" where: The PROPERTY attribute specifies the desired property. The optional exclamation point negates the output of the compare-operation. Other Boolean operators are currently not supported in property-based filters. The COMPARE_OPERATION attribute specifies one of the compare-operations listed in Table 20.1 “Property-based compare-operations”. The STRING attribute specifies the value that the text provided by the property is compared to. This value must be enclosed in quotation marks. To escape certain character inside the string for example a quotation mark " use the backslash character \. Table 20.1. Property-based compare-operations Compare-operation Description contains Checks whether the provided string matches any part of the text provided by the property. To perform case- insensitive comparisons use contains_i. isequal Compares the provided string against all of the text provided by the property. These two values must be exactly equal to match. startswith Checks whether the provided string is found exactly at the beginning of the text provided by the property. To perform case-insensitive comparisons use startswith_i. regex Compares the provided POSIX BRE Basic Regular Expression against the text provided by the property. ereregex Compares the provided POSIX ERE Extended Regular Expression regular expression against the text provided by the property. Syst em Administ rat ors Guide 378

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isempty Checks if the property is empty. The value is discarded. This is especially useful when working with normalized data where some fields may be populated based on normalization result. Compare-operation Description Example 20.2. Property-based Filters The following are a few examples of property-based filters that can be specified in /etc/rsyslog.conf. To select syslog messages which contain the string error in their message text use: :msg contains "error" The following filter selects syslog messages received from the host name host1: :hostname isequal "host1" To select syslog messages which do not contain any mention of the words fatal and error with any or no text between them for example fatal lib error type: :msg regex "fatal . error" Expression-based filters Expression-based filters select syslog messages according to defined arithmetic Boolean or string operations. Expression-based filters use rsyslogs own scripting language called RainerScript to build complex filters. The basic syntax of expression-based filter looks as follows: if EXPRESSION then ACTION else ACTION where: The EXPRESSION attribute represents an expression to be evaluated for example: msg startswith DEVNAME or syslogfacility-text local0. You can specify more than one expression in a single filter by using and and or operators. The ACTION attribute represents an action to be performed if the expression returns the value true. This can be a single action or an arbitrary complex script enclosed in curly braces. Expression-based filters are indicated by the keyword if at the start of a new line. The then keyword separates the EXPRESSION from the ACTION. Optionally you can employ the else keyword to specify what action is to be performed in case the condition is not met. With expression-based filters you can nest the conditions by using a script enclosed in curly braces as in Example 20.3 “Expression-based Filters”. The script allows you to use facility/priority-based filters inside the expression. On the other hand property-based filters are not recommended here. RainerScript supports regular expressions with specialized functions re_match and re_extract. ⁠Chapt er 2 0 . Viewing and Managing Log Files 379

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Example 20.3. Expression-based Filters The following expression contains two nested conditions. The log files created by a program called prog1 are split into two files based on the presence of the "test" string in the message. if programname prog1 then actiontype"omfile" file"/var/log/prog1.log" if msg contains test then actiontype"omfile" file"/var/log/prog1test.log" else actiontype"omfile" file"/var/log/prog1notest.log" See Section 20.12 “Online Documentation” for more examples of various expression-based filters. RainerScript is the basis for rsyslogs new configuration format see Section 20.3 “Using the New Configuration Format” 20.2.2. Actions Actions specify what is to be done with the messages filtered out by an already-defined selector. The following are some of the actions you can define in your rule: Saving syslog messages to log files The majority of actions specify to which log file a syslog message is saved. This is done by specifying a file path after your already-defined selector: FILTER PATH where FILTER stands for user-specified selector and PATH is a path of a target file. For instance the following rule is comprised of a selector that selects all cron syslog messages and an action that saves them into the /var/log/cron.log log file: cron. /var/log/cron.log By default the log file is synchronized every time a syslog message is generated. Use a dash mark - as a prefix of the file path you specified to omit syncing: FILTER -PATH Note that you might lose information if the system terminates right after a write attempt. However this setting can improve performance especially if you run programs that produce very verbose log messages. Your specified file path can be either static or dynamic. Static files are represented by a fixed file path as shown in the example above. Dynamic file paths can differ according to the received message. Dynamic file paths are represented by a template and a question mark prefix: FILTER DynamicFile Syst em Administ rat ors Guide 380

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where DynamicFile is a name of a predefined template that modifies output paths. You can use the dash prefix - to disable syncing also you can use multiple templates separated by a colon . For more information on templates see Section 20.2.3 “Generating Dynamic File Names”. If the file you specified is an existing terminal or /dev/console device syslog messages are sent to standard output using special terminal-handling or your console using special /dev/console-handling when using the X Window System respectively. Sending syslog messages over the network rsyslog allows you to send and receive syslog messages over the network. This feature allows you to administer syslog messages of multiple hosts on one machine. To forward syslog messages to a remote machine use the following syntax: zNUMBERHOST:PORT where: The at sign indicates that the syslog messages are forwarded to a host using the UDP protocol. To use the TCP protocol use two at signs with no space between them . The optional zNUMBER setting enables z lib compression for syslog messages. The NUMBER attribute specifies the level of compression from 1 – lowest to 9 – maximum. Compression gain is automatically checked by rsyslogd messages are compressed only if there is any compression gain and messages below 60 bytes are never compressed. The HOST attribute specifies the host which receives the selected syslog messages. The PORT attribute specifies the host machines port. When specifying an IPv6 address as the host enclose the address in square brackets . Example 20.4 . Sending syslog Messages over the Network The following are some examples of actions that forward syslog messages over the network note that all actions are preceded with a selector that selects all messages with any priority. To forward messages to 192.168.0.1 via the UDP protocol type: . 192.168.0.1 To forward messages to "example.com" using port 6514 and the TCP protocol use: . example.com:6514 The following compresses messages with z lib level 9 compression and forwards them to 2001:db8::1 using the UDP protocol . z92001:db8::1 Output channels Output channels are primarily used to specify the maximum size a log file can grow to. This ⁠Chapt er 2 0 . Viewing and Managing Log Files 381

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is very useful for log file rotation for more information see Section 20.2.5 “Log Rotation”. An output channel is basically a collection of information about the output action. Output channels are defined by the outchannel directive. To define an output channel in /etc/rsyslog.conf use the following syntax: outchannel NAME FILE_NAME MAX_SIZE ACTION where: The NAME attribute specifies the name of the output channel. The FILE_NAME attribute specifies the name of the output file. Output channels can write only into files not pipes terminal or other kind of output. The MAX_SIZE attribute represents the maximum size the specified file in FILE_NAME can grow to. This value is specified in bytes. The ACTION attribute specifies the action that is taken when the maximum size defined in MAX_SIZE is hit. To use the defined output channel as an action inside a rule type: FILTER :omfile:NAME Example 20.5. Output channel log rotation The following output shows a simple log rotation through the use of an output channel. First the output channel is defined via the outchannel directive: outchannel log_rotation /var/log/test_log.log 104857600 /home/joe/log_rotation_script and then it is used in a rule that selects every syslog message with any priority and executes the previously-defined output channel on the acquired syslog messages: . :omfile:log_rotation Once the limit in the example 100 MB is hit the /home/joe/log_rotation_script is executed. This script can contain anything from moving the file into a different folder editing specific content out of it or simply removing it. Sending syslog messages to specific users rsyslog can send syslog messages to specific users by specifying a user name of the user you want to send the messages to as in Example 20.7 “Specifying Multiple Actions”. To specify more than one user separate each user name with a comma . To send messages to every user that is currently logged on use an asterisk . Executing a program rsyslog lets you execute a program for selected syslog messages and uses the system call to execute the program in shell. To specify a program to be executed prefix it with a caret character . Consequently specify a template that formats the received message and passes it to the specified executable as a one line parameter for more information on templates see Section 20.2.3 “Templates”. Syst em Administ rat ors Guide 382

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FILTER EXECUTABLE TEMPLATE Here an output of the FILTER condition is processed by a program represented by EXECUTABLE. This program can be any valid executable. Replace TEMPLATE with the name of the formatting template. Example 20.6 . Executing a Program In the following example any syslog message with any priority is selected formatted with the template template and passed as a parameter to the test-program program which is then executed with the provided parameter: . test-programtemplate Warning When accepting messages from any host and using the shell execute action you may be vulnerable to command injection. An attacker may try to inject and execute commands in the program you specified to be executed in your action. To avoid any possible security threats thoroughly consider the use of the shell execute action. Storing syslog messages in a database Selected syslog messages can be directly written into a database table using the database writer action. The database writer uses the following syntax: :PLUGIN:DB_HOSTDB_NAMEDB_USERDB_PASSWORDTEMPLATE where: The PLUGIN calls the specified plug-in that handles the database writing for example the ommysql plug-in. The DB_HOST attribute specifies the database host name. The DB_NAME attribute specifies the name of the database. The DB_USER attribute specifies the database user. The DB_PASSWORD attribute specifies the password used with the aforementioned database user. The TEMPLATE attribute specifies an optional use of a template that modifies the syslog message. For more information on templates see Section 20.2.3 “Templates”. ⁠Chapt er 2 0 . Viewing and Managing Log Files 383

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Important Currently rsyslog provides support for MySQL and PostgreSQL databases only. In order to use the MySQL and PostgreSQL database writer functionality install the rsyslog-mysql and rsyslog-pgsql packages respectively. Also make sure you load the appropriate modules in your /etc/rsyslog.conf configuration file: ModLoad ommysql Output module for MySQL support ModLoad ompgsql Output module for PostgreSQL support For more information on rsyslog modules see Section 20.6 “Using Rsyslog Modules”. Alternatively you may use a generic database interface provided by the omlibdb module supports: Firebird/Interbase MS SQL Sybase SQLLite Ingres Oracle mSQL. Discarding syslog messages To discard your selected messages use the tilde character . FILTER The discard action is mostly used to filter out messages before carrying on any further processing. It can be effective if you want to omit some repeating messages that would otherwise fill the log files. The results of discard action depend on where in the configuration file it is specified for the best results place these actions on top of the actions list. Please note that once a message has been discarded there is no way to retrieve it in later configuration file lines. For instance the following rule discards any cron syslog messages: cron. Specifying Mult iple Act io ns For each selector you are allowed to specify multiple actions. To specify multiple actions for one selector write each action on a separate line and precede it with an ampersand character: FILTER ACTION ACTION ACTION Specifying multiple actions improves the overall performance of the desired outcome since the specified selector has to be evaluated only once. Example 20.7. Specifying Multiple Actions In the following example all kernel syslog messages with the critical priority crit are sent to user user1 processed by the template temp and passed on to the test-program executable and forwarded to 192.168.0.1 via the UDP protocol. Syst em Administ rat ors Guide 384

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kern.crit user1 test-programtemp 192.168.0.1 Any action can be followed by a template that formats the message. To specify a template suffix an action with a semicolon and specify the name of the template. For more information on templates see Section 20.2.3 “Templates”. Warning A template must be defined before it is used in an action otherwise it is ignored. In other words template definitions should always precede rule definitions in /etc/rsyslog.conf. 20.2.3. T emplates Any output that is generated by rsyslog can be modified and formatted according to your needs with the use of templates. To create a template use the following syntax in /etc/rsyslog.conf: template TEMPLATE_NAME"text PROPERTY more text" OPTION where: template is the template directive that indicates that the text following it defines a template. TEMPLATE_NAME is the name of the template. Use this name to refer to the template. Anything between the two quotation marks "…" is the actual template text. Within this text special characters such as \n for new line or \r for carriage return can be used. Other characters such as or " have to be escaped if you want to use those characters literally. The text specified between two percent signs specifies a property that allows you to access specific contents of a syslog message. For more information on properties see Section 20.2.3 “Properties”. The OPTION attribute specifies any options that modify the template functionality. The currently supported template options are sql and stdsql which are used for formatting the text as an SQL query. Note Note that the database writer checks whether the sql or stdsql options are specified in the template. If they are not the database writer does not perform any action. This is to prevent any possible security threats such as SQL injection. See section Storing syslog messages in a database in Section 20.2.2 “Actions” for more information. Generat ing Dynamic File Names Templates can be used to generate dynamic file names. By specifying a property as a part of the file ⁠Chapt er 2 0 . Viewing and Managing Log Files 385

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path a new file will be created for each unique property which is a convenient way to classify syslog messages. For example use the timegenerated property which extracts a time stamp from the message to generate a unique file name for each syslog message: template DynamicFile"/var/log/test_logs/timegenerated-test.log" Keep in mind that the template directive only specifies the template. You must use it inside a rule for it to take effect. In /etc/rsyslog.conf use the question mark in an action definition to mark the dynamic file name template: . DynamicFile Pro pert ies Properties defined inside a template between two percent signs enable access various contents of a syslog message through the use of a property replacer. To define a property inside a template between the two quotation marks "…" use the following syntax: PROPERTY_NAME:FROM_CHAR:TO_CHAR:OPTION where: The PROPERTY_NAME attribute specifies the name of a property. A list of all available properties and their detailed description can be found in the rsyslog.conf5 manual page under the section Available Properties. FROM_CHAR and TO_CHAR attributes denote a range of characters that the specified property will act upon. Alternatively regular expressions can be used to specify a range of characters. To do so set the letter R as the FROM_CHAR attribute and specify your desired regular expression as the TO_CHAR attribute. The OPTION attribute specifies any property options such as the lowercase option to convert the input to lowercase. A list of all available property options and their detailed description can be found in the rsyslog.conf5 manual page under the section Property Options. The following are some examples of simple properties: The following property obtains the whole message text of a syslog message: msg The following property obtains the first two characters of the message text of a syslog message: msg:1:2 The following property obtains the whole message text of a syslog message and drops its last line feed character: msg:::drop-last-lf The following property obtains the first 10 characters of the time stamp that is generated when the syslog message is received and formats it according to the RFC 3999 date standard. Syst em Administ rat ors Guide 386

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timegenerated:1:10:date-rfc3339 T emplat e Examples This section presents a few examples of rsyslog templates. Example 20.8 “A verbose syslog message template” shows a template that formats a syslog message so that it outputs the messages severity facility the time stamp of when the message was received the host name the message tag the message text and ends with a new line. Example 20.8. A verbose syslog message template template verbose "syslogseverity syslogfacility timegenerated HOSTNAME syslogtag msg\n" Example 20.9 “A wall message template” shows a template that resembles a traditional wall message a message that is send to every user that is logged in and has their mesg1 permission set to yes. This template outputs the message text along with a host name message tag and a time stamp on a new line using \r and \n and rings the bell using \7. Example 20.9 . A wall message template template wallmsg"\r\n\7Message from syslogdHOSTNAME at timegenerated ...\r\n syslogtag msg\n\r" Example 20.10 “A database formatted message template” shows a template that formats a syslog message so that it can be used as a database query. Notice the use of the sql option at the end of the template specified as the template option. It tells the database writer to format the message as an MySQL SQL query. Example 20.10. A database formatted message template template dbFormat"insert into SystemEvents Message Facility FromHost Priority DeviceReportedTime ReceivedAt InfoUnitID SysLogTag values msg syslogfacility HOSTNAME syslogpriority timereported:::date-mysql timegenerated:::date-mysql iut syslogtag" sql rsyslog also contains a set of predefined templates identified by the RSYSLOG_ prefix. These are reserved for the syslogs use and it is advisable to not create a template using this prefix to avoid conflicts. The following list shows these predefined templates along with their definitions. RSYSLOG_DebugFormat A special format used for troubleshooting property problems. "Debug line with all properties:\nFROMHOST: FROMHOST fromhost-ip: fromhost-ip HOSTNAME: HOSTNAME PRI: PRI\nsyslogtag syslogtag programname: programname ⁠Chapt er 2 0 . Viewing and Managing Log Files 387

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APP-NAME: APP-NAME PROCID: PROCID MSGID: MSGID\nTIMESTAMP: TIMESTAMP STRUCTURED-DATA: STRUCTURED-DATA\nmsg: msg\nescaped msg: msg:::drop- cc\nrawmsg: rawmsg\n\n\" RSYSLOG_SyslogProtocol23Format The format specified in IETFs internet-draft ietf-syslog-protocol-23 which is assumed to become the new syslog standard RFC. "PRI1 TIMESTAMP:::date-rfc3339 HOSTNAME APP-NAME PROCID MSGID STRUCTURED-DATA msg\n\" RSYSLOG_FileFormat A modern-style logfile format similar to TraditionalFileFormat but with high-precision time stamps and time zone information. "TIMESTAMP:::date-rfc3339 HOSTNAME syslogtagmsg:::sp-if-no- 1st-spmsg:::drop-last-lf\n\" RSYSLOG_TraditionalFileFormat The older default log file format with low-precision time stamps. "TIMESTAMP HOSTNAME syslogtagmsg:::sp-if-no-1st- spmsg:::drop-last-lf\n\" RSYSLOG_ForwardFormat A forwarding format with high-precision time stamps and time zone information. "PRITIMESTAMP:::date-rfc3339 HOSTNAME syslogtag:1:32msg:::sp-if-no-1st-spmsg\" RSYSLOG_TraditionalForwardFormat The traditional forwarding format with low-precision time stamps. "PRITIMESTAMP HOSTNAME syslogtag:1:32msg:::sp-if-no-1st- spmsg\" 20.2.4 . Global Directives Global directives are configuration options that apply to the rsyslogd daemon. They usually specify a value for a specific predefined variable that affects the behavior of the rsyslogd daemon or a rule that follows. All of the global directives must start with a dollar sign . Only one directive can be specified per line. The following is an example of a global directive that specifies the maximum size of the syslog message queue: MainMsgQueueSize 50000 The default size defined for this directive 10000 messages can be overridden by specifying a different value as shown in the example above. Syst em Administ rat ors Guide 388

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You can define multiple directives in your /etc/rsyslog.conf configuration file. A directive affects the behavior of all configuration options until another occurrence of that same directive is detected. Global directives can be used to configure actions queues and for debugging. A comprehensive list of all available configuration directives can be found in Section 20.12 “Online Documentation”. Currently a new configuration format has been developed that replaces the -based syntax see Section 20.3 “Using the New Configuration Format”. However classic global directives remain supported as a legacy format. 20.2.5. Log Rotation The following is a sample /etc/logrotate.conf configuration file: rotate log files weekly weekly keep 4 weeks worth of backlogs rotate 4 uncomment this if you want your log files compressed compress All of the lines in the sample configuration file define global options that apply to every log file. In our example log files are rotated weekly rotated log files are kept for four weeks and all rotated log files are compressed by gz ip into the .gz format. Any lines that begin with a hash sign are comments and are not processed. You may define configuration options for a specific log file and place it under the global options. However it is advisable to create a separate configuration file for any specific log file in the /etc/logrotate.d/ directory and define any configuration options there. The following is an example of a configuration file placed in the /etc/logrotate.d/ directory: /var/log/messages rotate 5 weekly postrotate /usr/bin/killall -HUP syslogd endscript The configuration options in this file are specific for the /var/log/messages log file only. The settings specified here override the global settings where possible. Thus the rotated /var/log/messages log file will be kept for five weeks instead of four weeks as was defined in the global options. The following is a list of some of the directives you can specify in your logrotate configuration file: weekly — Specifies the rotation of log files to be done weekly. Similar directives include: daily monthly yearly compress — Enables compression of rotated log files. Similar directives include: nocompress ⁠Chapt er 2 0 . Viewing and Managing Log Files 389

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compresscmd — Specifies the command to be used for compressing. uncompresscmd compressext — Specifies what extension is to be used for compressing. compressoptions — Specifies any options to be passed to the compression program used. delaycompress — Postpones the compression of log files to the next rotation of log files. rotate INTEGER — Specifies the number of rotations a log file undergoes before it is removed or mailed to a specific address. If the value 0 is specified old log files are removed instead of rotated. mail ADDRESS — This option enables mailing of log files that have been rotated as many times as is defined by the rotate directive to the specified address. Similar directives include: nomail mailfirst — Specifies that the just-rotated log files are to be mailed instead of the about-to- expire log files. maillast — Specifies that the about-to-expire log files are to be mailed instead of the just- rotated log files. This is the default option when mail is enabled. For the full list of directives and various configuration options see the logrotate5 manual page. 20.3. Using the New Configuration Format In rsyslog version 7 installed by default for Red Hat Enterprise Linux 7 in the rsyslog package a new configuration syntax is introduced. This new configuration format aims to be more powerful more intuitive and to prevent common mistakes by not permitting certain invalid constructs. The syntax enhancement is enabled by the new configuration processor that relies on RainerScript. The legacy format is still fully supported and it is used by default in the /etc/rsyslog.conf configuration file. RainerScript is a scripting language designed for processing network events and configuring event processors such as rsyslog. RainerScript was first used to define expression-based filters see Example 20.3 “Expression-based Filters”. The version of RainerScript in rsyslog version 7 implements the input and ruleset statements which permit the /etc/rsyslog.conf configuration file to be written in the new syntax. The new syntax differs mainly in that it is much more structured parameters are passed as arguments to statements such as input action template and module load. The scope of options is limited by blocks. This enhances readability and reduces the number of bugs caused by misconfiguration. There is also a significant performance gain. Some functionality is exposed in both syntaxes some only in the new one. Compare the configuration written with legacy-style parameters: InputFileName /tmp/inputfile InputFileTag tag1: InputFileStateFile inputfile-state InputRunFileMonitor and the same configuration with the use of the new format statement: inputtype"imfile" file"/tmp/inputfile" tag"tag1:" statefile"inputfile-state" Syst em Administ rat ors Guide 390

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This significantly reduces the number of parameters used in configuration improves readability and also provides higher execution speed. For more information on RainerScript statements and parameters see Section 20.12 “Online Documentation”. 20.3.1. Rulesets Leaving special directives aside rsyslog handles messages as defined by rules that consist of a filter condition and an action to be performed if the condition is true. With a traditionally written /etc/rsyslog.conf file all rules are evaluated in order of appearance for every input message. This process starts with the first rule and continues until all rules have been processed or until the message is discarded by one of the rules. However rules can be grouped into sequences called rulesets. With rulesets you can limit the effect of certain rules only to selected inputs or enhance the performance of rsyslog by defining a distinct set of actions bound to a specific input. In other words filter conditions that will be inevitably evaluated as false for certain types of messages can be skipped. The legacy ruleset definition in /etc/rsyslog.conf can look as follows: RuleSet rulesetname rule rule2 The rule ends when another rule is defined or the default ruleset is called as follows: RuleSet RSYSLOG_DefaultRuleset With the new configuration format in rsyslog 7 the input and ruleset statements are reserved for this operation. The new format ruleset definition in /etc/rsyslog.conf can look as follows: rulesetname"rulesetname" rule rule2 call rulesetname2 … Replace rulesetname with an identifier for your ruleset. The ruleset name cannot start with RSYSLOG_ since this namespace is reserved for use by rsyslog. RSYSLOG_DefaultRuleset then defines the default set of rules to be performed if the message has no other ruleset assigned. With rule and rule2 you can define rules in filter-action format mentioned above. With the call parameter you can nest rulesets by calling them from inside other ruleset blocks. After creating a ruleset you need to specify what input it will apply to: inputtype"input_type" port"port_num" ruleset"rulesetname" Here you can identify an input message by input_type which is an input module that gathered the message or by port_num – the port number. Other parameters such as file or tag can be specified for input. Replace rulesetname with a name of the ruleset to be evaluated against the message. In case an input message is not explicitly bound to a ruleset the default ruleset is triggered. You can also use the legacy format to define rulesets for more information see Section 20.12 “Online Documentation”. ⁠Chapt er 2 0 . Viewing and Managing Log Files 391

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Example 20.11. Using rulesets The following rulesets ensure different handling of remote messages coming from different ports. Add the following into /etc/rsyslog.conf: rulesetname"remote-6514" actiontype"omfile" file"/var/log/remote-6514" rulesetname"remote-601" cron. actiontype"omfile" file"/var/log/remote-601-cron" mail. actiontype"omfile" file"/var/log/remote-601-mail" inputtype"imtcp" port"6514" ruleset"remote-6514" inputtype"imtcp" port"601" ruleset"remote-601" Rulesets shown in the above example define log destinations for the remote input from two ports in case of port 601 messages are sorted according to the facility. Then the TCP input is enabled and bound to rulesets. Note that you must load the required modules imtcp for this configuration to work. 20.3.2. Compatibility with sysklogd The compatibility mode specified via the -c option exists in rsyslog version 5 but not in version 7. Also the sysklogd-style command-line options are deprecated and configuring rsyslog through these command-line options should be avoided. However you can use several templates and directives to configure rsyslogd to emulate sysklogd-like behavior. For more information on various rsyslogd options see the rsyslogd8manual page. 20.4. Working with Queues in Rsyslog Queues are used to pass content mostly syslog messages between components of rsyslog. With queues rsyslog is capable of processing multiple messages simultaneously and to apply several actions to a single message at once. The data flow inside rsyslog can be illustrated as follows: Syst em Administ rat ors Guide 392

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Figure 20.1. Message Flow in Rsyslog Whenever rsyslog receives a message it passes this message to the preprocessor and then places it into the main message queue. Messages wait there to be dequeued and passed to the rule processor. The rule processor is a parsing and filtering engine. Here the rules defined in /etc/rsyslog.conf are applied. Based on these rules the rule processor evaluates which actions are to be performed. Each action has its own action queue. Messages are passed through this queue to the respective action processor which creates the final output. Note that at this point several actions can run simultaneously on one message. For this purpose a message is duplicated and passed to multiple action processors. Only one queue per action is possible. Depending on configuration the messages can be sent right to the action processor without action queuing. This is the behavior of direct queues see below. In case the output action fails the action processor notifies the action queue which then takes an unprocessed element back and after some time interval the action is attempted again. To sum up there are two positions where queues stand in rsyslog: either in front of the rule processor as a single main message queue or in front of various types of output actions as action queues. Queues provide two main advantages that both lead to increased performance of message processing: they serve as buffers that decouple producers and consumers in the structure of rsyslog they allow for parallelization of actions performed on messages Apart from this queues can be configured with several directives to provide optimal performance for your system. These configuration options are covered in the following sections. ⁠Chapt er 2 0 . Viewing and Managing Log Files 393

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Warning If an output plug-in is unable to deliver a message it is stored in the preceding message queue. If the queue fills the inputs block until it is no longer full. This will prevent new messages from being logged via the blocked queue. In the absence of separate action queues this can have severe consequences such as preventing SSH logging which in turn can prevent SSH access. Therefore it is advised to use dedicated action queues for outputs which are forwarded over a network or to a database. 20.4 .1. Defining Queues Based on where the messages are stored there are several types of queues: direct in-memory disk and disk-assisted in-memory queues that are most widely used. You can choose one of these types for the main message queue and also for action queues. Add the following into /etc/rsyslog.conf: objectQueueType queue_type Here you can apply the setting for the main message queue replace object with MainMsg or for an action queue replace object with Action. Replace queue_type with one of direct linkedlist or fixedarray which are in-memory queues or disk. The default setting for a main message queue is the FixedArray queue with a limit of 10000 messages. Action queues are by default set as Direct queues. Direct Queues For many simple operations such as when writing output to a local file building a queue in front of an action is not needed. To avoid queuing use: objectQueueType Direct Replace object with MainMsg or with Action to use this option to the main message queue or for an action queue respectively. With direct queue messages are passed directly and immediately from the producer to the consumer. Disk Queues Disk queues store messages strictly on a hard drive which makes them highly reliable but also the slowest of all possible queuing modes. This mode can be used to prevent the loss of highly important log data. However disk queues are not recommended in most use cases. To set a disk queue type the following into /etc/rsyslog.conf: objectQueueType Disk Replace object with MainMsg or with Action to use this option to the main message queue or for an action queue respectively. Disk queues are written in parts with a default size 10 Mb. This default size can be modified with the following configuration directive: objectQueueMaxFileSize size Syst em Administ rat ors Guide 394

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where size represents the specified size of disk queue part. The defined size limit is not restrictive rsyslog always writes one complete queue entry even if it violates the size limit. Each part of a disk queue matches with an individual file. The naming directive for these files looks as follows: objectQueueFilename name This sets a name prefix for the file followed by a 7-digit number starting at one and incremented for each file. In-memo ry Queues With in-memory queue the enqueued messages are held in memory which makes the process very fast. The queued data is lost if the computer is power cycled or shut down. However you can use the ActionQueueSaveOnShutdown setting to save the data before shutdown. There are two types of in-memory queues: FixedArray queue — the default mode for the main message queue with a limit of 10000 elements. This type of queue uses a fixed pre-allocated array that holds pointers to queue elements. Due to these pointers even if the queue is empty a certain amount of memory is consumed. However FixedArray offers the best run time performance and is optimal when you expect a relatively low number of queued messages and high performance. LinkedList queue — here all structures are dynamically allocated in a linked list thus the memory is allocated only when needed. LinkedList queues handle occasional message bursts very well. In general use LinkedList queues when in doubt. Compared to FixedArray it consumes less memory and lowers the processing overhead. Use the following syntax to configure in-memory queues: objectQueueType LinkedList objectQueueType FixedArray Replace object with MainMsg or with Action to use this option to the main message queue or for an action queue respectively. Disk-Assist ed In-memo ry Queues Both disk and in-memory queues have their advantages and rsyslog lets you combine them in disk- assisted in-memory queues. To do so configure a normal in-memory queue and then add the objectQueueFileName directive to define a file name for disk assistance. This queue then becomes disk-assisted which means it couples an in-memory queue with a disk queue to work in tandem. The disk queue is activated if the in-memory queue is full or needs to persist after shutdown. With a disk-assisted queue you can set both disk-specific and in-memory specific configuration parameters. This type of queue is probably the most commonly used it is especially useful for potentially long-running and unreliable actions. To specify the functioning of a disk-assisted in-memory queue use the so-called watermarks: objectQueueHighWatermark number objectQueueLowWatermark number ⁠Chapt er 2 0 . Viewing and Managing Log Files 395

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Replace object with MainMsg or with Action to use this option to the main message queue or for an action queue respectively. Replace number with a number of enqueued messages. When an in- memory queue reaches the number defined by the high watermark it starts writing messages to disk and continues until the in-memory queue size drops to the number defined with the low watermark. Correctly set watermarks minimize unnecessary disk writes but also leave memory space for message bursts since writing to disk files is rather lengthy. Therefore the high watermark must be lower than the whole queue capacity set with objectQueueSize. The difference between the high watermark and the overall queue size is a spare memory buffer reserved for message bursts. On the other hand setting the high watermark too low will turn on disk assistance unnecessarily often. Example 20.12. Reliable Forwarding of Log Messages to a Server Rsyslog is often used to maintain a centralized logging system where log messages are forwarded to a server over the network. To avoid message loss when the server is not available it is advisable to configure an action queue for the forwarding action. This way messages that failed to be sent are stored locally until the server is reachable again. Note that such queues are not configurable for connections using the UDP protocol. Procedure 20.1. Forwarding To a Single Server Suppose the task is to forward log messages from the system to a server with host name example.com and to configure an action queue to buffer the messages in case of a server outage. To do so perform the following steps: Use the following configuration in /etc/rsyslog.conf or create a file with the following content in the /etc/rsyslog.d/ directory: ActionQueueType LinkedList ActionQueueFileName example_fwd ActionResumeRetryCount -1 ActionQueueSaveOnShutdown on . example.com:6514 Where: ActionQueueType enables a LinkedList in-memory queue ActionFileName defines a disk storage in this case the backup files are created in the /var/lib/rsyslog/ directory with the example_fwd prefix the ActionResumeRetryCount -1 setting prevents rsyslog from dropping messages when retrying to connect if server is not responding enabled ActionQueueSaveOnShutdown saves in-memory data if rsyslog shuts down the last line forwards all received messages to the logging server port specification is optional. With the above configuration rsyslog keeps messages in memory if the remote server is not reachable. A file on disk is created only if rsyslog runs out of the configured memory queue space or needs to shut down which benefits the system performance. Procedure 20.2. Forwarding To Multiple Servers The process of forwarding log messages to multiple servers is similar to the previous procedure: Syst em Administ rat ors Guide 396

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Each destination server requires a separate forwarding rule action queue specification and backup file on disk. For example use the following configuration in /etc/rsyslog.conf or create a file with the following content in the /etc/rsyslog.d/ directory: ActionQueueType LinkedList ActionQueueFileName example_fwd1 ActionResumeRetryCount -1 ActionQueueSaveOnShutdown on . example1.com ActionQueueType LinkedList ActionQueueFileName example_fwd2 ActionResumeRetryCount -1 ActionQueueSaveOnShutdown on . example2.com 20.4 .2. Creating a New Directory for rsyslog Log Files Rsyslog runs as the syslogd daemon and is managed by SELinux. Therefore all files to which rsyslog is required to write to must have the appropriate SELinux file context. Procedure 20.3. Creating a New Working Directory 1. If required to use a different directory to store working files create a directory as follows: mkdir /rsyslog 2. Install utilities to manage SELinux policy: yum install policycoreutils-python 3. Set the SELinux directory context type to be the same as the /var/lib/rsyslog/ directory: semanage fcontext -a -t syslogd_var_lib_t /rsyslog 4. Apply the SELinux context: restorecon -R -v /rsyslog restorecon reset /rsyslog context unconfined_u:object_r:default_t:s0- unconfined_u:object_r:syslogd_var_lib_t:s0 5. If required check the SELinux context as follows: ls -Zd /rsyslog drwxr-xr-x. root root system_u:object_r:syslogd_var_lib_t:s0 /rsyslog 6. Create subdirectories as required. For example: mkdir /rsyslog/work/ ⁠Chapt er 2 0 . Viewing and Managing Log Files 397

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The subdirectories will be created with the same SELinux context as the parent directory. 7. Add the following line in /etc/rsyslog.conf immediately before it is required to take effect: WorkDirectory /rsyslog/work This setting will remain in effect until the next WorkDirectory directive is encountered while parsing the configuration files. 20.4 .3. Managing Queues All types of queues can be further configured to match your requirements. You can use several directives to modify both action queues and the main message queue. Currently there are more than 20 queue parameters available see Section 20.12 “Online Documentation”. Some of these settings are used commonly others such as worker thread management provide closer control over the queue behavior and are reserved for advanced users. With advanced settings you can optimize rsyslogs performance schedule queuing or modify the behavior of a queue on system shutdown. Limit ing Queue Size You can limit the number of messages that queue can contain with the following setting: objectQueueHighWatermark number Replace object with MainMsg or with Action to use this option to the main message queue or for an action queue respectively. Replace number with a number of enqueued messages. You can set the queue size only as the number of messages not as their actual memory size. The default queue size is 10000 messages for the main message queue and ruleset queues and 1000 for action queues. Disk assisted queues are unlimited by default and can not be restricted with this directive but you can reserve them physical disk space in bytes with the following settings: objectQueueMaxDiscSpace number Replace object with MainMsg or with Action. When the size limit specified by number is hit messages are discarded until sufficient amount of space is freed by dequeued messages. Discarding Messages When a queue reaches a certain number of messages you can discard less important messages in order to save space in the queue for entries of higher priority. The threshold that launches the discarding process can be set with the so-called discard mark: objectQueueDiscardMark number Replace object with MainMsg or with Action to use this option to the main message queue or for an action queue respectively. Here number stands for a number of messages that have to be in the queue to start the discarding process. To define which messages to discard use: objectQueueDiscardSeverity priority Syst em Administ rat ors Guide 398

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Replace priority with one of the following keywords or with a number: debug 7 info 6 notice 5 warning 4 err 3 crit 2 alert 1 and emerg 0. With this setting both newly incoming and already queued messages with lower than defined priority are erased from the queue immediately after the discard mark is reached. Using T imeframes You can configure rsyslog to process queues during a specific time period. With this option you can for example transfer some processing into off-peak hours. To define a time frame use the following syntax: objectQueueDequeueTimeBegin hour objectQueueDequeueTimeEnd hour With hour you can specify hours that bound your time frame. Use the 24-hour format without minutes. Co nfiguring Wo rker T hreads A worker thread performs a specified action on the enqueued message. For example in the main message queue a worker task is to apply filter logic to each incoming message and enqueue them to the relevant action queues. When a message arrives a worker thread is started automatically. When the number of messages reaches a certain number another worker thread is turned on. To specify this number use: objectQueueWorkerThreadMinimumMessages number Replace number with a number of messages that will trigger a supplemental worker thread. For example with number set to 100 a new worker thread is started when more than 100 messages arrive. When more than 200 messages arrive the third worker thread starts and so on. However too many working threads running in parallel becomes ineffective so you can limit the maximum number of them by using: objectQueueWorkerThreads number where number stands for a maximum number of working threads that can run in parallel. For the main message queue the default limit is 1 thread. Once a working thread has been started it keeps running until an inactivity timeout appears. To set the length of timeout type: objectQueueWorkerTimeoutThreadShutdown time Replace time with the duration set in milliseconds. Without this setting a zero timeout is applied and a worker thread is terminated immediately when it runs out of messages. If you specify time as -1 no thread will be closed. Bat ch Dequeuing To increase performance you can configure rsyslog to dequeue multiple messages at once. To set the upper limit for such dequeueing use: objectQueueDequeueBatchSize number ⁠Chapt er 2 0 . Viewing and Managing Log Files 399

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Replace number with the maximum number of messages that can be dequeued at once. Note that a higher setting combined with a higher number of permitted working threads results in greater memory consumption. T erminat ing Queues When terminating a queue that still contains messages you can try to minimize the data loss by specifying a time interval for worker threads to finish the queue processing: objectQueueTimeoutShutdown time Specify time in milliseconds. If after that period there are still some enqueued messages workers finish the current data element and then terminate. Unprocessed messages are therefore lost. Another time interval can be set for workers to finish the final element: objectQueueTimeoutActionCompletion time In case this timeout expires any remaining workers are shut down. To save data at shutdown use: objectQueueTimeoutSaveOnShutdown time If set all queue elements are saved to disk before rsyslog terminates. 20.4 .4 . Using the New Syntax for rsyslog queues In the new syntax available in rsyslog 7 queues are defined inside the action object that can be used both separately or inside a ruleset in /etc/rsyslog.conf. The format of an action queue is as follows: actiontype"action_type" queue.size"queue_size" queue.type"queue_type" queue.filename"file_name" Replace action_type with the name of the module that is to perform the action and replace queue_size with a maximum number of messages the queue can contain. For queue_type choose disk or select from one of the in-memory queues: direct linkedlist or fixedarray. For file_name specify only a file name not a path. Note that if creating a new directory to hold log files the SELinux context must be set. See Section 20.4.2 “Creating a New Directory for rsyslog Log Files” for an example. Example 20.13. Defining an Action Queue To configure the output action with an asynchronous linked-list based action queue which can hold a maximum of 10000 messages enter a command as follows: actiontype"omfile" queue.size"10000" queue.type"linkedlist" queue.filename"logfile" The rsyslog 7 syntax for a direct action queues is as follows: . actiontype"omfile" file"/var/lib/rsyslog/log_file Syst em Administ rat ors Guide 4 00

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The rsyslog 7 syntax for an action queue with multiple parameters can be written as follows: . actiontype"omfile" queue.filename"log_file" queue.type"linkedlist" queue.size"10000" The default work directory or the last work directory to be set will be used. If required to use a different work directory add a line as follows before the action queue: globalworkDirectory"/directory" Example 20.14 . Forwarding To a Single Server Using the New Syntax The following example is based on the procedure Procedure 20.1 “Forwarding To a Single Server” in order to show the difference between the traditional sysntax and the rsyslog 7 syntax. The omfwd plug-in is used to provide forwarding over UDP or TCP. The default is UDP. As the plug-in is built in it does not have to be loaded. Use the following configuration in /etc/rsyslog.conf or create a file with the following content in the /etc/rsyslog.d/ directory: . actiontype"omfwd" queue.type"linkedlist" queue.filename"example_fwd" action.resumeRetryCount"-1" queue.saveOnShutdown"on" target"example.com" port"6514" protocol"tcp" Where: queue.type"linkedlist" enables a LinkedList in-memory queue queue.filename defines a disk storage. The backup files are created with the example_fwd prefix in the working directory specified by the preceding global workDirectory directive the action.resumeRetryCount -1 setting prevents rsyslog from dropping messages when retrying to connect if server is not responding enabled queue.saveOnShutdown"on" saves in-memory data if rsyslog shuts down the last line forwards all received messages to the logging server port specification is optional. 20.5. Configuring rsyslog on a Logging Server The rsyslog service provides facilities both for running a logging server and for configuring individual systems to send their log files to the logging server. See Example 20.12 “Reliable Forwarding of Log Messages to a Server” for information on client rsyslog configuration. The rsyslog service must be installed on the system that you intend to use as a logging server and all systems that will be configured to send logs to it. Rsyslog is installed by default in Red Hat Enterprise Linux 7. If required to ensure that it is enter the following command as root: ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 01

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yum install rsyslog The default protocol and port for syslog traffic is UDP and 514 as listed in the /etc/services file. However rsyslog defaults to using TCP on port 514. In the configuration file /etc/rsyslog.conf TCP is indicated by . Other ports are sometimes used in examples however SELinux is only configured to allow sending and receiving on the following ports by default: semanage port -l | grep syslog syslogd_port_t tcp 6514 601 syslogd_port_t udp 514 6514 601 The semanage utility is provided as part of the policycoreutils-python package. If required install the package as follows: yum install policycoreutils-python In addition by default the SELinux type for rsyslog rsyslogd_t is configured to permit sending and receiving to the remote shell rsh port with SELinux type rsh_port_t which defaults to TCP on port 514. Therefore it is not necessary to use semanage to explicitly permit TCP on port 514. For example to check what SELinux is set to permit on port 514 enter a command as follows: semanage port -l | grep 514 output omitted rsh_port_t tcp 514 syslogd_port_t tcp 6514 601 syslogd_port_t udp 514 6514 601 For more information on SELinux see Red Hat Enterprise Linux 7 SELinux Users and Administrators Guide. Perform the steps in the following procedures on the system that you intend to use as your logging server. All steps in these procedure must be made as the root user. Procedure 20.4 . Configure SELinux to Permit rsyslog Traffic on a Port If required to use a new port for rsyslog traffic follow this procedure on the logging server and the clients. For example to send and receive TCP traffic on port 10514 proceed as follows: 1. semanage port -a -t syslogd_port_t -p tcp 10514 2. Review the SELinux ports by entering the following command: semanage port -l | grep syslog 3. If the new port was already configured in /etc/rsyslog.conf restart rsyslog now for the change to take effect: service rsyslog restart 4. Verify which ports rsyslog is now listening to: Syst em Administ rat ors Guide 4 02

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netstat -tnlp | grep rsyslog tcp 0 0 0.0.0.0:10514 0.0.0.0: LISTEN 2528/rsyslogd tcp 0 0 :::10514 ::: LISTEN 2528/rsyslogd See the semanage-port8 manual page for more information on the semanage port command. Procedure 20.5. Configuring firewalld Configure firewalld to allow incoming rsyslog traffic. For example to allow TCP traffic on port 10514 proceed as follows: 1. firewall-cmd --zonezone --add-port10514/tcp success Where zone is the zone of the interface to use. Note that these changes will not persist after the next system start. To make permanent changes to the firewall repeat the commands adding the --permanent option. For more information on opening and closing ports in firewalld see the Red Hat Enterprise Linux 7 Security Guide. 2. To verify the above settings use a command as follows: firewall-cmd --list-all public default active interfaces: eth0 sources: services: dhcpv6-client ssh ports: 10514/tcp masquerade: no forward-ports: icmp-blocks: rich rules: Procedure 20.6 . Configuring rsyslog to Receive and Sort Remote Log Messages 1. Open the /etc/rsyslog.conf file in a text editor and proceed as follows: a. Add these lines below the modules section but above the Provides UDP syslog reception section: Define templates before the rules that use them Per-Host Templates for Remote Systems template TmplAuthpriv "/var/log/remote/auth/HOSTNAME/PROGRAMNAME:::secpath- replace.log" template TmplMsg "/var/log/remote/msg/HOSTNAME/PROGRAMNAME:::secpath- replace.log" b. Replace the default Provides TCP syslog reception section with the following: ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 03

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Provides TCP syslog reception ModLoad imtcp Adding this ruleset to process remote messages RuleSet remote1 authpriv. TmplAuthpriv .infomail.noneauthpriv.nonecron.none TmplMsg RuleSet RSYSLOG_DefaultRuleset End the rule set by switching back to the default rule set InputTCPServerBindRuleset remote1 Define a new input and bind it to the "remote1" rule set InputTCPServerRun 10514 Save the changes to the /etc/rsyslog.conf file. 2. The rsyslog service must be running on both the logging server and the systems attempting to log to it. a. Use the systemctl command to start the rsyslog service. systemctl start rsyslog b. To ensure the rsyslog service starts automatically in future enter the following command as root: systemctl enable rsyslog Your log server is now configured to receive and store log files from the other systems in your environment. 20.5.1. Using T he New T emplate Syntax on a Logging Server Rsyslog 7 has a number of different templates styles. The string template most closely resembles the legacy format. Reproducing the templates from the example above using the string format would look as follows: templatename"TmplAuthpriv" type"string" string"/var/log/remote/auth/HOSTNAME/PROGRAMNAME:::secpath- replace.log" templatename"TmplMsg" type"string" string"/var/log/remote/msg/HOSTNAME/PROGRAMNAME:::secpath- replace.log" These templates can also be written in the list format as follows: templatename"TmplAuthpriv" type"list" constantvalue"/var/log/remote/auth/" propertyname"hostname" constantvalue"/" propertyname"programname" SecurePath"replace" constantvalue".log" Syst em Administ rat ors Guide 4 04

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templatename"TmplMsg" type"list" constantvalue"/var/log/remote/msg/" propertyname"hostname" constantvalue"/" propertyname"programname" SecurePath"replace" constantvalue".log" This template text format might be easier to read for those new to rsyslog and therefore can be easier to adapt as requirements change. To complete the change to the new syntax we need to reproduce the module load command add a rule set and then bind the rule set to the protocol port and ruleset: moduleload"imtcp" rulesetname"remote1" authpriv. actiontype"omfile" DynaFile"TmplAuthpriv" .infomail.noneauthpriv.nonecron.none actiontype"omfile" DynaFile"TmplMsg" inputtype"imtcp" port"10514" ruleset"remote1" 20.6. Using Rsyslog Modules Due to its modular design rsyslog offers a variety of modules which provide additional functionality. Note that modules can be written by third parties. Most modules provide additional inputs see Input Modules below or outputs see Output Modules below. Other modules provide special functionality specific to each module. The modules may provide additional configuration directives that become available after a module is loaded. To load a module use the following syntax: ModLoad MODULE where ModLoad is the global directive that loads the specified module and MODULE represents your desired module. For example if you want to load the Text File Input Module imfile that enables rsyslog to convert any standard text files into syslog messages specify the following line in the /etc/rsyslog.conf configuration file: ModLoad imfile rsyslog offers a number of modules which are split into the following main categories: Input Modules — Input modules gather messages from various sources. The name of an input module always starts with the im prefix such as imfile and imjournal. Output Modules — Output modules provide a facility to issue message to various targets such as sending across a network storing in a database or encrypting. The name of an output module always starts with the om prefix such as omsnmp omrelp and so on. ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 05

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Parser Modules — These modules are useful in creating custom parsing rules or to parse malformed messages. With moderate knowledge of the C programming language you can create your own message parser. The name of a parser module always starts with the pm prefix such as pmrfc5424 pmrfc3164 and so on. Message Modification Modules — Message modification modules change content of syslog messages. Names of these modules start with the mm prefix. Message Modification Modules such as mmanon mmnormalize or mmjsonparse are used for anonymization or normalization of messages. String Generator Modules — String generator modules generate strings based on the message content and strongly cooperate with the template feature provided by rsyslog. For more information on templates see Section 20.2.3 “Templates”. The name of a string generator module always starts with the sm prefix such as smfile or smtradfile. Library Modules — Library modules provide functionality for other loadable modules. These modules are loaded automatically by rsyslog when needed and cannot be configured by the user. A comprehensive list of all available modules and their detailed description can be found at http://www.rsyslog.com/doc/rsyslog_conf_modules.html. Warning Note that when rsyslog loads any modules it provides them with access to some of its functions and data. This poses a possible security threat. To minimize security risks use trustworthy modules only. 20.6.1. Importing T ext Files The Text File Input Module abbreviated as imfile enables rsyslog to convert any text file into a stream of syslog messages. You can use imfile to import log messages from applications that create their own text file logs. To load imfile add the following into /etc/rsyslog.conf: ModLoad imfile InputFilePollInterval int It is sufficient to load imfile once even when importing multiple files. The InputFilePollInterval global directive specifies how often rsyslog checks for changes in connected text files. The default interval is 10 seconds to change it replace int with a time interval specified in seconds. To identify the text files to import use the following syntax in /etc/rsyslog.conf: File 1 InputFileName path_to_file InputFileTag tag: InputFileStateFile state_file_name InputFileSeverity severity InputFileFacility facility InputRunFileMonitor File 2 InputFileName path_to_file2 ... Syst em Administ rat ors Guide 4 06

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Four settings are required to specify an input text file: replace path_to_file with a path to the text file. replace tag: with a tag name for this message. replace state_file_name with a unique name for the state file. State files which are stored in the rsyslog working directory keep cursors for the monitored files marking what partition has already been processed. If you delete them whole files will be read in again. Make sure that you specify a name that does not already exist. add the InputRunFileMonitor directive that enables the file monitoring. Without this setting the text file will be ignored. Apart from the required directives there are several other settings that can be applied on the text input. Set the severity of imported messages by replacing severity with an appropriate keyword. Replace facility with a keyword to define the subsystem that produced the message. The keywords for severity and facility are the same as those used in facility/priority-based filters see Section 20.2.1 “Filters”. Example 20.15. Importing Text Files The Apache HTTP server creates log files in text format. To apply the processing capabilities of rsyslog to apache error messages first use the imfile module to import the messages. Add the following into /etc/rsyslog.conf: ModLoad imfile InputFileName /var/log/httpd/error_log InputFileTag apache-error: InputFileStateFile state-apache-error InputRunFileMonitor 20.6.2. Exporting Messages to a Database Processing of log data can be faster and more convenient when performed in a database rather than with text files. Based on the type of DBMS used choose from various output modules such as ommysql ompgsql omoracle or ommongodb. As an alternative use the generic omlibdbi output module that relies on the libdbi library. The omlibdbi module supports database systems Firebird/Interbase MS SQL Sybase SQLite Ingres Oracle mSQL MySQL and PostgreSQL. Example 20.16 . Exporting Rsyslog Messages to a Database To store the rsyslog messages in a MySQL database add the following into /etc/rsyslog.conf: ModLoad ommysql ActionOmmysqlServerPort 1234 . :ommysql:database-serverdatabase-namedatabase-useriddatabase- password ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 07

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First the output module is loaded then the communication port is specified. Additional information such as name of the server and the database and authentication data is specified on the last line of the above example. 20.6.3. Enabling Encrypted T ransport Confidentiality and integrity in network transmissions can be provided by either the TLS or GSSAPI encryption protocol. Transport Layer Security TLS is a cryptographic protocol designed to provide communication security over the network. When using TLS rsyslog messages are encrypted before sending and mutual authentication exists between the sender and receiver. For configuring TLS see Section 20.6.3 “Configuring Encrypted Message Transfer with TLS”. Generic Security Service API GSSAPI is an application programming interface for programs to access security services. To use it in connection with rsyslog you must have a functioning Kerberos environment. For configuring GSSAPI see Section 20.6.3 “Configuring Encrypted Message Transfer with GSSAPI”. Co nfiguring Encrypt ed Message T ransfer wit h T LS To use encrypted transport through TLS you need to configure both the server and the client. 1. Create public key private key and certificate file see Section 12.1.11 “Generating a New Key and Certificate”. 2. On the server side configure the following in the /etc/rsyslog.conf configuration file: a. Set the gtls netstream driver as the default driver: DefaultNetstreamDriver gtls b. Provide paths to certificate files: DefaultNetstreamDriverCAFile path_ca.pem DefaultNetstreamDriverCertFile path_cert.pem DefaultNetstreamDriverKeyFile path_key.pem Replace: path_ca.pem with a path to your public key path_cert.pem with a path to the certificate file path_key.pem with a path to the private key c. Load the imtcp module: ModLoad imtcp d. Start the server and set driver options: InputTCPServerStreamDriverMode number InputTCPServerStreamDriverAuthMode anon InputTCPServerRun port Syst em Administ rat ors Guide 4 08

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Replace: number to specify the driver mode. To enable TCP-only mode use 1 port with the port number at which to start a listener for example 10514 The anon setting means that the client is not authenticated. 3. On the client side configure the following in the /etc/rsyslog.conf configuration file: a. Load the public key: DefaultNetstreamDriverCAFile path_ca.pem Replace path_ca.pem with a path to the public key. b. Set the gtls netstream driver as the default driver: DefaultNetstreamDriver gtls c. Configure the driver and specify what action will be performed: InputTCPServerStreamDriverMode number InputTCPServerStreamDriverAuthMode anon . server.net:port Replace number anon and port with the same values as on the server. On the last line in the above listing an example action forwards messages from the server to the specified TCP port. Co nfiguring Encrypt ed Message T ransfer wit h GSSAPI In rsyslog interaction with GSSAPI is provided by the imgssapi module. To turn on the GSSAPI transfer mode: 1. Put the following configuration in /etc/rsyslog.conf: ModLoad imgssapi This directive loads the imgssapi module. 2. Specify the input as follows: InputGSSServerServiceName name InputGSSServerPermitPlainTCP on InputGSSServerMaxSessions number InputGSSServerRun port Replace name with the name of the GSS server. Replace number to set the maximum number of sessions supported. This number is not limited by default. Replace port with a selected port on which you want to start a GSS server. ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 09

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The InputGSSServerPermitPlainTCP on setting permits the server to receive also plain TCP messages on the same port. This is off by default. Note The imgssapi module is initialized as soon as the configuration file reader encounters the InputGSSServerRun directive in the /etc/rsyslog.conf configuration file. The supplementary options configured after InputGSSServerRun are therefore ignored. For configuration to take effect all imgssapi configuration options must be placed before InputGSSServerRun. Example 20.17. Using GSSAPI The following configuration enables a GSS server on the port 1514 that also permits to receive plain tcp syslog messages on the same port. ModLoad imgssapi InputGSSServerPermitPlainTCP on InputGSSServerRun 1514 20.6.4 . Using RELP Reliable Event Logging Protocol RELP is a networking protocol for data logging in computer networks. It is designed to provide reliable delivery of event messages which makes it useful in environments where message loss is not acceptable. To configure RELP you need to configure both the server and the client using the /etc/rsyslog.conf file. 1. To configure the client: a. Load the required modules: moduleload"imuxsock" moduleload"omrelp" moduleload"imtcp" b. Configure the TCP input as follows: inputtype"imtcp" port"port″ Replace port to start a listener at the required port. c. Configure the transport settings: actiontype"omrelp" target"target_IP″ port"target_port″ Replace target_IP and target_port with the IP address and port that identify the target server. 2. To configure the server: Syst em Administ rat ors Guide 4 10

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a. Configure loading the module: moduleload"imuxsock" moduleload"imrelp" ruleset"relp" b. Configure the TCP input similarly to the client configuration: inputtype"imrelp" port"target_port″ Replace target_port with the same value as on the clients. c. Configure the rules and choose an action to be performed. In the following example log_path specifies the path for storing messages: ruleset name"relp" actiontype"omfile" file"log_path" 20.7. Interaction of Rsyslog and Journal As mentioned above Rsyslog and Journal the two logging applications present on your system have several distinctive features that make them suitable for specific use cases. In many situations it is useful to combine their capabilities for example to create structured messages and store them in a file database see Section 20.8 “Structured Logging with Rsyslog”. A communication interface needed for this cooperation is provided by input and output modules on the side of Rsyslog and by the Journals communication socket. By default rsyslogd uses the imjournal module as a default input mode for journal files. With this module you import not only the messages but also the structured data provided by journald. Also older data can be imported from journald unless forbidden with the ImjournalIgnorePreviousMessages directive. See Section 20.8.1 “Importing Data from Journal” for basic configuration of imjournal. As an alternative configure rsyslogd to read from the socket provided by journal as an output for syslog-based applications. The path to the socket is /run/systemd/journal/syslog. Use this option when you want to maintain plain rsyslog messages. Compared to imjournal the socket input currently offers more features such as ruleset binding or filtering. To import Journal data trough the socket use the following configuration in /etc/rsyslog.conf: ModLoad imuxsock OmitLocalLogging off The above syntax loads the imuxsock module and turns off the OmitLocalLogging directive which enables the import trough the system socket. The path to this socket is specified separately in /etc/rsyslog.d/listen.conf as follows: SystemLogSocketName /run/systemd/journal/syslog You can also output messages from Rsyslog to Journal with the omjournal module. Configure the output in /etc/rsyslog.conf as follows: ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 11

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ModLoad omjournal . :omjournal: For instance the following configuration forwards all received messages on tcp port 10514 to the Journal: ModLoad imtcp ModLoad omjournal RuleSet remote . :omjournal: InputTCPServerBindRuleset remote InputTCPServerRun 10514 20.8. Structured Logging with Rsyslog On systems that produce large amounts of log data it can be convenient to maintain log messages in a structured format. With structured messages it is easier to search for particular information to produce statistics and to cope with changes and inconsistencies in message structure. Rsyslog uses the JSON JavaScript Object Notation format to provide structure for log messages. Compare the following unstructured log message: Oct 25 10:20:37 localhost anacron1395: Jobs will be executed sequentially with a structured one: "timestamp":"2013-10-25T10:20:37" "host":"localhost" "program":"anacron" "pid":"1395" "msg":"Jobs will be executed sequentially" Searching structured data with use of key-value pairs is faster and more precise than searching text files with regular expressions. The structure also lets you to search for the same entry in messages produced by various applications. Also JSON files can be stored in a document database such as MongoDB which provides additional performance and analysis capabilities. On the other hand a structured message requires more disk space than the unstructured one. In rsyslog log messages with meta data are pulled from Journal with use of the imjournal module. With the mmjsonparse module you can parse data imported from Journal and from other sources and process them further for example as a database output. For parsing to be successful mmjsonparse requires input messages to be structured in a way that is defined by the Lumberjack project. The Lumberjack project aims to add structured logging to rsyslog in a backward-compatible way. To identify a structured message Lumberjack specifies the cee: string that prepends the actual JSON structure. Also Lumberjack defines the list of standard field names that should be used for entities in the JSON string. For more information on Lumberjack see Section 20.12 “Online Documentation”. The following is an example of a lumberjack-formatted message: Syst em Administ rat ors Guide 4 12

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cee: "pid":17055 "uid":1000 "gid":1000 "appname":"logger" "msg":"Message text." To build this structure inside Rsyslog a template is used see Section 20.8.2 “Filtering Structured Messages”. Applications and servers can employ the libumberlog library to generate messages in the lumberjack-compliant form. For more information on libumberlog see Section 20.12 “Online Documentation”. 20.8.1. Importing Data from Journal The imjournal module is Rsyslogs input module to natively read the journal files see Section 20.7 “Interaction of Rsyslog and Journal”. Journal messages are then logged in text format as other rsyslog messages. However with further processing it is possible to translate meta data provided by Journal into a structured message. To import data from Journal to Rsyslog use the following configuration in /etc/rsyslog.conf: ModLoad imjournal imjournalPersistStateInterval number_of_messages imjournalStateFile path imjournalRatelimitInterval seconds imjournalRatelimitBurst burst_number ImjournalIgnorePreviousMessages off/on With number_of_messages you can specify how often the journal data must be saved. This will happen each time the specified number of messages is reached. Replace path with a path to the state file. This file tracks the journal entry that was the last one processed. With seconds you set the length of the rate limit interval. The number of messages processed during this interval can not exceed the value specified in burst_number. The default setting is 20000 messages per 600 seconds. Rsyslog discards messages that come after the maximum burst within the time frame specified. With ImjournalIgnorePreviousMessages you can ignore messages that are currently in Journal and import only new messages which is used when there is no state file specified. The default setting is off. Please note that if this setting is off and there is no state file all messages in the Journal are processed even if they were already processed in a previous rsyslog session. Note You can use imjournal simultaneously with imuxsock module that is the traditional system log input. However to avoid message duplication you must prevent imuxsock from reading the Journals system socket. To do so use the OmitLocalLogging directive: ModLoad imuxsock ModLoad imjournal OmitLocalLogging on AddUnixListenSocket /run/systemd/journal/syslog ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 13

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You can translate all data and meta data stored by Journal into structured messages. Some of these meta data entries are listed in Example 20.19 “Verbose journalctl Output” for a complete list of journal fields see the systemd.journal-fields7 manual page. For example it is possible to focus on kernel journal fields that are used by messages originating in the kernel. 20.8.2. Filtering Structured Messages To create a lumberjack-formatted message that is required by rsyslogs parsing module use the following template: templatename"CEETemplate" type"string" string"TIMESTAMP HOSTNAME syslogtag cee: all-json\n" This template prepends the cee: string to the JSON string and can be applied for example when creating an output file with omfile module. To access JSON field names use the prefix. For example the following filter condition searches for messages with specific hostname and UID: hostname "hostname" UID "UID" 20.8.3. Parsing JSON The mmjsonparse module is used for parsing structured messages. These messages can come from Journal or from other input sources and must be formatted in a way defined by the Lumberjack project. These messages are identified by the presence of the cee: string. Then mmjsonparse checks if the JSON structure is valid and then the message is parsed. To parse lumberjack-formatted JSON messages with mmjsonparse use the following configuration in the /etc/rsyslog.conf: ModLoad mmjsonparse . :mmjsonparse: In this example the mmjsonparse module is loaded on the first line then all messages are forwarded to it. Currently there are no configuration parameters available for mmjsonparse. 20.8.4 . Storing Messages in the MongoDB Rsyslog supports storing JSON logs in the MongoDB document database through the ommongodb output module. To forward log messages into MongoDB use the following syntax in the /etc/rsyslog.conf configuration parameters for ommongodb are available only in the new configuration format see Section 20.3 “Using the New Configuration Format”: ModLoad ommongodb . actiontype"ommongodb" server"DB_server" serverport"port" db"DB_name" collection"collection_name" uid"UID" pwd"password" Replace DB_server with the name or address of the MongoDB server. Specify port to select a non- standard port from the MongoDB server. The default port value is 0 and usually there is no need to change this parameter. Syst em Administ rat ors Guide 4 14

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With DB_name you identify to which database on the MongoDB server you want to direct the output. Replace collection_name with the name of a collection in this database. In MongoDB collection is a group of documents the equivalent of an RDBMS table. You can set your login details by replacing UID and password. You can shape the form of the final database output with use of templates. By default rsyslog uses a template based on standard lumberjack field names. 20.9. Debugging Rsyslog To run rsyslogd in debugging mode use the following command: rsyslogd -dn With this command rsyslogd produces debugging information and prints it to the standard output. The -n stands for "no fork". You can modify debugging with environmental variables for example you can store the debug output in a log file. Before starting rsyslogd type the following on the command line: export RSYSLOG_DEBUGLOG"path" export RSYSLOG_DEBUG"Debug" Replace path with a desired location for the file where the debugging information will be logged. For a complete list of options available for the RSYSLOG_DEBUG variable see the related section in the rsyslogd8 manual page. To check if syntax used in the /etc/rsyslog.conf file is valid use: rsyslogd -N 1 Where 1 represents level of verbosity of the output message. This is a forward compatibility option because currently only one level is provided. However you must add this argument to run the validation. 20.10. Using the Journal The Journal is a component of systemd that is responsible for viewing and management of log files. It can be used in parallel or in place of a traditional syslog daemon such as rsyslogd. The Journal was developed to address problems connected with traditional logging. It is closely integrated with the rest of the system supports various logging technologies and access management for the log files. Logging data is collected stored and processed by the Journals journald service. It creates and maintains binary files called journals based on logging information that is received from the kernel from user processes from standard output and standard error output of system services or via its native API. These journals are structured and indexed which provides relatively fast seek times. Journal entries can carry a unique identifier. The journald service collects numerous meta data fields for each log message. The actual journal files are secured and therefore cannot be manually edited. 20.10.1. Viewing Log Files ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 15

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To access the journal logs use the journalctl tool. For a basic view of the logs type as root: journalctl An output of this command is a list of all log files generated on the system including messages generated by system components and by users. The structure of this output is similar to one used in /var/log/messages/ but with certain improvements: the priority of entries is marked visually. Lines of error priority and higher are highlighted with red color and a bold font is used for lines with notice and warning priority the time stamps are converted for the local time zone of your system all logged data is shown including rotated logs the beginning of a boot is tagged with a special line Example 20.18. Example Output of journalctl The following is an example output provided by the journalctl tool. When called without parameters the listed entries begin with a time stamp then the host name and application that performed the operation is mentioned followed by the actual message. This example shows the first three entries in the journal log: journalctl -- Logs begin at Thu 2013-08-01 15:42:12 CEST end at Thu 2013-08-01 15:48:48 CEST. -- Aug 01 15:42:12 localhost systemd-journal54: Allowing runtime journal files to grow to 49.7M. Aug 01 15:42:12 localhost kernel: Initializing cgroup subsys cpuset Aug 01 15:42:12 localhost kernel: Initializing cgroup subsys cpu ... In many cases only the latest entries in the journal log are relevant. The simplest way to reduce journalctl output is to use the -n option that lists only the specified number of most recent log entries: journalctl -n Number Replace Number with the number of lines to be shown. When no number is specified journalctl displays the ten most recent entries. The journalctl command allows controlling the form of the output with the following syntax: journalctl -o form Replace form with a keyword specifying a desired form of output. There are several options such as verbose which returns full-structured entry items with all fields export which creates a binary stream suitable for backups and network transfer and json which formats entries as JSON data structures. For the full list of keywords see the journalctl1 manual page. Example 20.19 . Verbose journalctl Output Syst em Administ rat ors Guide 4 16

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To view full meta data about all entries type: journalctl -o verbose ... Fri 2013-08-02 14:41:22 CEST se1021ca1b81e4fc688fad6a3ea21d35bi55cb78c81449c920439da57da7bd5c56 a770m27cc _BOOT_ID78c81449c920439da57da7bd5c56a770 PRIORITY5 SYSLOG_FACILITY3 _TRANSPORTsyslog _MACHINE_ID69d27b356a94476da859461d3a3bc6fd _HOSTNAMElocalhost.localdomain _PID562 _COMMdbus-daemon _EXE/usr/bin/dbus-daemon _CMDLINE/bin/dbus-daemon --system --addresssystemd: --nofork --nopidfile --systemd-activation _SYSTEMD_CGROUP/system/dbus.service _SYSTEMD_UNITdbus.service SYSLOG_IDENTIFIERdbus SYSLOG_PID562 _UID81 _GID81 _SELINUX_CONTEXTsystem_u:system_r:system_dbusd_t:s0-s0:c0.c1023 MESSAGEsystem Successfully activated service net.reactivated.Fprint _SOURCE_REALTIME_TIMESTAMP1375447282839181 ... This example lists fields that identify a single log entry. These meta data can be used for message filtering as shown in Section 20.10.4 “Advanced Filtering”. For a complete description of all possible fields see the systemd.journal-fields7 manual page. 20.10.2. Access Control By default Journal users without root privileges can only see log files generated by them. The system administrator can add selected users to the adm group which grants them access to complete log files. To do so type as root: usermod -a -G adm username Here replace username with a name of the user to be added to the adm group. This user then receives the same output of the journalctl command as the root user. Note that access control only works when persistent storage is enabled for Journal. 20.10.3. Using T he Live View When called without parameters journalctl shows the full list of entries starting with the oldest entry collected. With the live view you can supervise the log messages in real time as new entries are continuously printed as they appear. To start journalctl in live view mode type: ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 17

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journalctl -f This command returns a list of the ten most current log lines. The journalctl utility then stays running and waits for new changes to show them immediately. 20.10.4 . Filtering Messages The output of the journalctl command executed without parameters is often extensive therefore you can use various filtering methods to extract information to meet your needs. Filt ering by Prio rit y Log messages are often used to track erroneous behavior on the system. To view only entries with a selected or higher priority use the following syntax: journalctl -p priority Here replace priority with one of the following keywords or with a number: debug 7 info 6 notice 5 warning 4 err 3 crit 2 alert 1 and emerg 0. Example 20.20. Filtering by Priority To view only entries with error or higher priority use: journalctl -p err Filt ering by T ime To view log entries only from the current boot type: journalctl -b If you reboot your system just occasionally the -b will not significantly reduce the output of journalctl. In such cases time-based filtering is more helpful: journalctl --sincevalue --untilvalue With --since and --until you can view only log messages created within a specified time range. You can pass values to these options in form of date or time or both as shown in the following example. Example 20.21. Filtering by Time and Priority Filtering options can be combined to reduce the set of results according to specific requests. For example to view the warning or higher priority messages from a certain point in time type: journalctl -p warning --since"2013-3-16 23:59:59" Advanced Filt ering Syst em Administ rat ors Guide 4 18

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Example 20.19 “Verbose journalctl Output” lists a set of fields that specify a log entry and can all be used for filtering. For a complete description of meta data that systemd can store see the systemd.journal-fields7 manual page. This meta data is collected for each log message without user intervention. Values are usually text-based but can take binary and large values fields can have multiple values assigned though it is not very common. To view a list of unique values that occur in a specified field use the following syntax: journalctl -F fieldname Replace fieldname with a name of a field you are interested in. To show only log entries that fit a specific condition use the following syntax: journalctl fieldnamevalue Replace fieldname with a name of a field and value with a specific value contained in that field. As a result only lines that match this condition are returned. Note As the number of meta data fields stored by systemd is quite large it is easy to forget the exact name of the field of interest. When unsure type: journalctl and press the Tab key two times. This shows a list of available field names. Tab completion based on context works on field names so you can type a distinctive set of letters from a field name and then press Tab to complete the name automatically. Similarly you can list unique values from a field. Type: journalctl fieldname and press Tab two times. This serves as an alternative to journalctl -F fieldname. You can specify multiple values for one field: journalctl fieldnamevalue1 fieldnamevalue2 ... Specifying two matches for the same field results in a logical OR combination of the matches. Entries matching value1 or value2 are displayed. Also you can specify multiple field-value pairs to further reduce the output set: journalctl fieldname1value fieldname2value ... If two matches for different field names are specified they will be combined with a logical AND. Entries have to match both conditions to be shown. With use of the + symbol you can set a logical OR combination of matches for multiple fields: ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 19

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journalctl fieldname1value + fieldname2value ... This command returns entries that match at least one of the conditions not only those that match both of them. Example 20.22. Advanced filtering To display entries created by avahi-daemon.service or crond.service under user with UID 70 use the following command: journalctl _UID70 _SYSTEMD_UNITavahi-daemon.service _SYSTEMD_UNITcrond.service Since there are two values set for the _SYSTEMD_UNIT field both results will be displayed but only when matching the _UID70 condition. This can be expressed simply as: UID70 and avahi or cron. You can apply the aforementioned filtering also in the live-view mode to keep track of the latest changes in the selected group of log entries: journalctl -f fieldnamevalue ... 20.10.5. Enabling Persistent Storage By default Journal stores log files only in memory or a small ring-buffer in the /run/log/journal/ directory. This is sufficient to show recent log history with journalctl. This directory is volatile log data is not saved permanently. With the default configuration syslog reads the journal logs and stores them in the /var/log/ directory. With persistent logging enabled journal files are stored in /var/log/journal which means they persist after reboot. Journal can then replace rsyslog for some users but see the chapter introduction. Enabled persistent storage has the following advantages Richer data is recorded for troubleshooting in a longer period of time For immediate troubleshooting richer data is available after a reboot Server console currently reads data from journal not log files Persistent storage has also certain disadvantages: Even with persistent storage the amount of data stored depends on free memory there is no guarantee to cover a specific time span More disk space is needed for logs To enable persistent storage for Journal create the journal directory manually as shown in the following example. As root type: mkdir -p /var/log/journal/ Then restart journald to apply the change: systemctl restart systemd-journald Syst em Administ rat ors Guide 4 20

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20.11. Managing Log Files in a Graphical Environment As an alternative to the aforementioned command-line utilities Red Hat Enterprise Linux 7 provides an accessible GUI for managing log messages. 20.11.1. Viewing Log Files Most log files are stored in plain text format. You can view them with any text editor such as Vi or Emacs. Some log files are readable by all users on the system however root privileges are required to read most log files. To view system log files in an interactive real-time application use the System Log. Note In order to use the System Log first ensure the gnome-system-log package is installed on your system by running as root: yum install gnome-system-log For more information on installing packages with Yum see Section 8.2.4 “Installing Packages”. After you have installed the gnome-system-log package open the System Log by clicking Applications → System Tools → System Log or type the following command at a shell prompt: gnome-system-log The application only displays log files that exist thus the list might differ from the one shown in Figure 20.2 “System Log”. ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 21

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Figure 20.2. System Log The System Log application lets you filter any existing log file. Click on the button marked with the gear symbol to view the menu select Filters → Manage Filters to define or edit the desired filter. Figure 20.3. System Log - Filters Adding or editing a filter lets you define its parameters as is shown in Figure 20.4 “System Log - defining a filter”. Syst em Administ rat ors Guide 4 22

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Figure 20.4 . System Log - defining a filter When defining a filter the following parameters can be edited: Name — Specifies the name of the filter. Regular Expression — Specifies the regular expression that will be applied to the log file and will attempt to match any possible strings of text in it. Effect Highlight — If checked the found results will be highlighted with the selected color. You may select whether to highlight the background or the foreground of the text. Hide — If checked the found results will be hidden from the log file you are viewing. When you have at least one filter defined it can be selected from the Filters menu and it will automatically search for the strings you have defined in the filter and highlight or hide every successful match in the log file you are currently viewing. ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 23

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Figure 20.5. System Log - enabling a filter When you select the Show matches only option only the matched strings will be shown in the log file you are currently viewing. 20.11.2. Adding a Log File To add a log file you want to view in the list select File → Open. This will display the Open Log window where you can select the directory and file name of the log file you want to view. Figure 20.6 “System Log - adding a log file” illustrates the Open Log window. Syst em Administ rat ors Guide 4 24

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Figure 20.6 . System Log - adding a log file Click on the Open button to open the file. The file is immediately added to the viewing list where you can select it and view its contents. Note The System Log also allows you to open log files zipped in the .gz format. 20.11.3. Monitoring Log Files System Log monitors all opened logs by default. If a new line is added to a monitored log file the log name appears in bold in the log list. If the log file is selected or displayed the new lines appear in bold at the bottom of the log file. Figure 20.7 “System Log - new log alert” illustrates a new alert in the cron log file and in the messages log file. Clicking on the messages log file displays the logs in the file with the new lines in bold. ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 25

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Figure 20.7. System Log - new log alert 20.12. Additional Resources For more information on how to configure the rsyslog daemon and how to locate view and monitor log files see the resources listed below. Installed Documentation rsyslogd8 — The manual page for the rsyslogd daemon documents its usage. rsyslog.conf5 — The manual page named rsyslog.conf documents available configuration options. logrotate8 — The manual page for the logrotate utility explains in greater detail how to configure and use it. journalctl1 — The manual page for the journalctl daemon documents its usage. journald.conf5 — This manual page documents available configuration options. systemd.journal-fields7 — This manual page lists special Journal fields. Installable Documentation /usr/share/doc/rsyslogversion/html/index.html — This file which is provided by the rsyslog-doc package from the Optional channel contains information on rsyslog. See Section 8.5.7 “Adding the Optional and Supplementary Repositories” for more information on Red Hat additional channels. Before accessing the documentation you must run the following command as root: Syst em Administ rat ors Guide 4 26

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yum install rsyslog-doc Online Documentation The rsyslog home page offers additional documentation configuration examples and video tutorials. Make sure to consult the documents relevant to the version you are using: RainerScript documentation on the rsyslog Home Page — Commented summary of data types expressions and functions available in RainerScript. rsyslog version 7 documentation on the rsyslog home page — Version 7 of rsyslog is available for Red Hat Enterprise Linux 7 in the rsyslog package. Description of queues on the rsyslog Home Page — General information on various types of message queues and their usage. See Also Chapter 5 Gaining Privileges documents how to gain administrative privileges by using the su and sudo commands. Chapter 9 Managing Services with systemd provides more information on systemd and documents how to use the systemctl command to manage system services. ⁠Chapt er 2 0 . Viewing and Managing Log Files 4 27

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Chapter 21. Automating System Tasks Tasks also known as jobs can be configured to run automatically within a specified period of time on a specified date or when the system load average decreases below 0.8. Red Hat Enterprise Linux is pre-configured to run important system tasks to keep the system updated. For example the slocate database used by the locate command is updated daily. A system administrator can use automated tasks to perform periodic backups monitor the system run custom scripts and so on. Red Hat Enterprise Linux comes with the following automated task utilities: cron anacron at and batch. Every utility is intended for scheduling a different job type: while Cron and Anacron schedule recurring jobs At and Batch schedule one-time jobs refer to Section 21.1 “Cron and Anacron” and Section 21.2 “At and Batch” respectively. Red Hat Enterprise Linux 7 supports the use of systemd.timer for executing a job at a specific time. See man systemd.timer5 for more information. 21.1. Cron and Anacron Both Cron and Anacron are daemons that can schedule execution of recurring tasks to a certain point in time defined by the exact time day of the month month day of the week and week. Cron jobs can run as often as every minute. However the utility assumes that the system is running continuously and if the system is not on at the time when a job is scheduled the job is not executed. On the other hand Anacron remembers the scheduled jobs if the system is not running at the time when the job is scheduled. The job is then executed as soon as the system is up. However Anacron can only run a job once a day. 21.1.1. Installing Cron and Anacron To install Cron and Anacron you need to install the cronie package with Cron and the cronie-anacron package with Anacron cronie-anacron is a sub-package of cronie. To determine if the packages are already installed on your system issue the following command: rpm -q cronie cronie-anacron The command returns full names of the cronie and cronie-anacron packages if already installed or notifies you that the packages are not available. To install these packages use the yum command in the following form as root: yum install package For example to install both Cron and Anacron type the following at a shell prompt: yum install cronie cronie-anacron For more information on how to install new packages in Red Hat Enterprise Linux see Section 8.2.4 “Installing Packages”. Syst em Administ rat ors Guide 4 28

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21.1.2. Running the Crond Service The cron and anacron jobs are both picked by the crond service. This section provides information on how to start stop and restart the crond service and shows how to configure it to start automatically at boot time. For more information on how to manage system service in Red Hat Enterprise Linux 7 in general see Chapter 9 Managing Services with systemd. 21.1.2.1. St art ing and St o pping t he Cro n Service To determine if the service is running use the following command: systemctl status crond.service To run the crond service in the current session type the following at a shell prompt as root: systemctl start crond.service To configure the service to start automatically at boot time use the following command as root: systemctl enable crond.service 21.1.2.2. St o pping t he Cro n Service To stop the crond service in the current session type the following at a shell prompt as root: systemctl stop crond.service To prevent the service from starting automatically at boot time use the following command as root: systemctl disable crond.service 21.1.2.3. Rest art ing t he Cro n Service To restart the crond service type the following at a shell prompt as root: systemctl restart crond.service This command stops the service and starts it again in quick succession. 21.1.3. Configuring Anacron Jobs The main configuration file to schedule jobs is the /etc/anacrontab file which can be only accessed by the root user. The file contains the following: SHELL/bin/sh PATH/sbin:/bin:/usr/sbin:/usr/bin MAILTOroot the maximal random delay added to the base delay of the jobs RANDOM_DELAY45 the jobs will be started during the following hours only START_HOURS_RANGE3-22 ⁠Chapt er 2 1 . Aut omat ing Syst em T asks 4 29

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period in days delay in minutes job-identifier command 1 5 cron.daily nice run-parts /etc/cron.daily 7 25 cron.weekly nice run-parts /etc/cron.weekly monthly 45 cron.monthly nice run-parts /etc/cron.monthly The first three lines define the variables that configure the environment in which the anacron tasks run: SHELL — shell environment used for running jobs in the example the Bash shell PATH — paths to executable programs MAILTO — username of the user who receives the output of the anacron jobs by email If the MAILTO variable is not defined MAILTO the email is not sent. The next two variables modify the scheduled time for the defined jobs: RANDOM_DELAY — maximum number of minutes that will be added to the delay in minutes variable which is specified for each job The minimum delay value is set by default to 6 minutes. If RANDOM_DELAY is for example set to 12 then between 6 and 12 minutes are added to the delay in minutes for each job in that particular anacrontab. RANDOM_DELAY can also be set to a value below 6 including 0. When set to 0 no random delay is added. This proves to be useful when for example more computers that share one network connection need to download the same data every day. START_HOURS_RANGE — interval when scheduled jobs can be run in hours In case the time interval is missed for example due to a power failure the scheduled jobs are not executed that day. The remaining lines in the /etc/anacrontab file represent scheduled jobs and follow this format: period in days delay in minutes job-identifier command period in days — frequency of job execution in days The property value can be defined as an integer or a macro daily weekly monthly where daily denotes the same value as integer 1 weekly the same as 7 and monthly specifies that the job is run once a month regardless of the length of the month. delay in minutes — number of minutes anacron waits before executing the job The property value is defined as an integer. If the value is set to 0 no delay applies. job-identifier — unique name referring to a particular job used in the log files command — command to be executed The command can be either a command such as ls /proc /tmp/proc or a command which executes a custom script. Any lines that begin with a hash sign are comments and are not processed. 21.1.3.1. Examples o f Anacro n Jo bs Syst em Administ rat ors Guide 4 30

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The following example shows a simple /etc/anacrontab file: SHELL/bin/sh PATH/sbin:/bin:/usr/sbin:/usr/bin MAILTOroot the maximal random delay added to the base delay of the jobs RANDOM_DELAY30 the jobs will be started during the following hours only START_HOURS_RANGE16-20 period in days delay in minutes job-identifier command 1 20 dailyjob nice run-parts /etc/cron.daily 7 25 weeklyjob /etc/weeklyjob.bash monthly 45 monthlyjob ls /proc /tmp/proc All jobs defined in this anacrontab file are randomly delayed by 6-30 minutes and can be executed between 16:00 and 20:00. The first defined job is triggered daily between 16:26 and 16:50 RANDOM_DELAY is between 6 and 30 minutes the delay in minutes property adds 20 minutes. The command specified for this job executes all present programs in the /etc/cron.daily/ directory using the run-parts script the run-parts scripts accepts a directory as a command-line argument and sequentially executes every program in the directory. See the run-parts man page for more information on the run-parts script. The second job executes the weeklyjob.bash script in the /etc directory once a week. The third job runs a command which writes the contents of /proc to the /tmp/proc file ls /proc /tmp/proc once a month. 21.1.4 . Configuring Cron Jobs The configuration file for cron jobs is /etc/crontab which can be only modified by the root user. The file contains the following: SHELL/bin/bash PATH/sbin:/bin:/usr/sbin:/usr/bin MAILTOroot HOME/ For details see man 4 crontabs Example of job definition: .---------------- minute 0 - 59 | .------------- hour 0 - 23 | | .---------- day of month 1 - 31 | | | .------- month 1 - 12 OR janfebmarapr ... | | | | .---- day of week 0 - 6 Sunday0 or 7 OR sunmontuewedthufrisat | | | | | user-name command to be executed The first three lines contain the same variable definitions as an anacrontab file: SHELL PATH and MAILTO. For more information about these variables see Section 21.1.3 “Configuring Anacron Jobs”. ⁠Chapt er 2 1 . Aut omat ing Syst em T asks 4 31

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In addition the file can define the HOME variable. The HOME variable defines the directory which will be used as the home directory when executing commands or scripts run by the job. The remaining lines in the /etc/crontab file represent scheduled jobs and have the following format: minute hour day month day of week username command The following define the time when the job is to be run: minute — any integer from 0 to 59 hour — any integer from 0 to 23 day — any integer from 1 to 31 must be a valid day if a month is specified month — any integer from 1 to 12 or the short name of the month such as jan or feb day of week — any integer from 0 to 7 where 0 or 7 represents Sunday or the short name of the week such as sun or mon The following define other job properties: username — specifies the user under which the jobs are run. command — the command to be executed. The command can be either a command such as ls /proc /tmp/proc or a command which executes a custom script. For any of the above values an asterisk can be used to specify all valid values. If you for example define the month value as an asterisk the job will be executed every month within the constraints of the other values. A hyphen - between integers specifies a range of integers. For example 1-4 means the integers 1 2 3 and 4. A list of values separated by commas specifies a list. For example 3468 indicates exactly these four integers. The forward slash / can be used to specify step values. The value of an integer will be skipped within a range following the range with /integer. For example the minute value defined as 0-59/2 denotes every other minute in the minute field. Step values can also be used with an asterisk. For instance if the month value is defined as /3 the task will run every third month. Any lines that begin with a hash sign are comments and are not processed. Users other than root can configure cron tasks with the crontab utility. The user-defined crontabs are stored in the /var/spool/cron/ directory and executed as if run by the users that created them. To create a crontab as a specific user login as that user and type the command crontab -e to edit the users crontab with the editor specified in the VISUAL or EDITOR environment variable. The file uses the same format as /etc/crontab. When the changes to the crontab are saved the crontab is stored according to the user name and written to the file /var/spool/cron/username. To list the contents of the current users crontab file use the crontab -l command. The /etc/cron.d/ directory contains files that have the same syntax as the /etc/crontab file. Only root is allowed to create and modify files in this directory. Syst em Administ rat ors Guide 4 32

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Note The cron daemon checks the /etc/anacrontab file the /etc/crontab file the /etc/cron.d/ directory and the /var/spool/cron/ directory every minute for changes and the detected changes are loaded into memory. It is therefore not necessary to restart the daemon after an anacrontab or a crontab file have been changed. 21.1.5. Controlling Access to Cron To restrict the access to Cron you can use the /etc/cron.allow and /etc/cron.deny files. These access control files use the same format with one user name on each line. Mind that no whitespace characters are permitted in either file. If the cron.allow file exists only users listed in the file are allowed to use cron and the cron.deny file is ignored. If the cron.allow file does not exist users listed in the cron.deny file are not allowed to use Cron. The Cron daemon crond does not have to be restarted if the access control files are modified. The access control files are checked each time a user tries to add or delete a cron job. The root user can always use cron regardless of the user names listed in the access control files. You can control the access also through Pluggable Authentication Modules PAM. The settings are stored in the /etc/security/access.conf file. For example after adding the following line to the file no other user but the root user can create crontabs: -:ALL EXCEPT root :cron The forbidden jobs are logged in an appropriate log file or when using crontab -e returned to the standard output. For more information see the access.conf.5 manual page. 21.1.6. Black and White Listing of Cron Jobs Black and white listing of jobs is used to define parts of a job that do not need to be executed. This is useful when calling the run-parts script on a Cron directory such as /etc/cron.daily/: if the user adds programs located in the directory to the job black list the run-parts script will not execute these programs. To define a black list create a jobs.deny file in the directory that run-parts scripts will be executing from. For example if you need to omit a particular program from /etc/cron.daily/ create the /etc/cron.daily/jobs.deny file. In this file specify the names of the programs to be omitted from execution only programs located in the same directory can be enlisted. If a job runs a command which runs the programs from the /etc/cron.daily/ directory such as run-parts /etc/cron.daily the programs defined in the jobs.deny file will not be executed. To define a white list create a jobs.allow file. The principles of jobs.deny and jobs.allow are the same as those of cron.deny and cron.allow described in section Section 21.1.5 “Controlling Access to Cron”. 21.2. At and Batch While Cron is used to schedule recurring tasks the At utility is used to schedule a one-time task at a ⁠Chapt er 2 1 . Aut omat ing Syst em T asks 4 33

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specific time and the Batch utility is used to schedule a one-time task to be executed when the system load average drops below 0.8. 21.2.1. Installing At and Batch To determine if the at package is already installed on your system issue the following command: rpm -q at The command returns the full name of the at package if already installed or notifies you that the package is not available. To install the packages use the yum command in the following form as root: yum install package For example to install both At and Batch type the following at a shell prompt: yum install at For more information on how to install new packages in Red Hat Enterprise Linux see Section 8.2.4 “Installing Packages”. 21.2.2. Running the At Service The At and Batch jobs are both picked by the atd service. This section provides information on how to start stop and restart the atd service and shows how to configure it to start automatically at boot time. For more information on how to manage system services in Red Hat Enterprise Linux 7 in general see Chapter 9 Managing Services with systemd. 21.2.2.1. St art ing and St o pping t he At Service To determine if the service is running use the following command: systemctl status atd.service To run the atd service in the current session type the following at a shell prompt as root: systemctl start atd.service To configure the service to start automatically at boot time use the following command as root: systemctl enable atd.service Note It is recommended that you configure your system to start the atd service automatically at boot time. 21.2.2.2. St o pping t he At Service Syst em Administ rat ors Guide 4 34

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To stop the atd service type the following at a shell prompt as root: systemctl stop atd.service To prevent the service from starting automatically at boot time use the following command as root: systemctl disable atd.service 21.2.2.3. Rest art ing t he At Service To restart the atd service type the following at a shell prompt as root: systemctl restart atd.service This command stops the service and starts it again in quick succession. 21.2.3. Configuring an At Job To schedule a one-time job for a specific time with the At utility do the following: 1. On the command line type the command at TIME where TIME is the time when the command is to be executed. The TIME argument can be defined in any of the following formats: HH:MM specifies the exact hour and minute For example 04:00 specifies 4:00 a.m. midnight specifies 12:00 a.m. noon specifies 12:00 p.m. teatime specifies 4:00 p.m. MONTHDAYYEAR format For example January 15 2012 specifies the 15th day of January in the year 2012. The year value is optional. MMDDYY MM/DD/YY or MM.DD.YY formats For example 011512 for the 15th day of January in the year 2012. now + TIME where TIME is defined as an integer and the value type: minutes hours days or weeks. For example now + 5 days specifies that the command will be executed at the same time five days from now. The time must be specified first followed by the optional date. For more information about the time format see the /usr/share/doc/at-version/timespec text file. If the specified time has past the job is executed at the time the next day. 2. In the displayed at prompt define the job commands: A. Type the command the job should execute and press Enter. Optionally repeat the step to provide multiple commands. B. Enter a shell script at the prompt and press Enter after each line in the script. The job will use the shell set in the users SHELL environment the users login shell or /bin/sh whichever is found first. ⁠Chapt er 2 1 . Aut omat ing Syst em T asks 4 35

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3. Once finished press Ctrl+D on an empty line to exit the prompt. If the set of commands or the script tries to display information to standard output the output is emailed to the user. To view the list of pending jobs use the atq command. See Section 21.2.5 “Viewing Pending Jobs” for more information. You can also restrict the usage of the at command. For more information see Section 21.2.7 “Controlling Access to At and Batch” for details. 21.2.4 . Configuring a Batch Job The Batch application executes the defined one-time tasks when the system load average decreases below 0.8. To define a Batch job do the following: 1. On the command line type the command batch. 2. In the displayed at prompt define the job commands: A. Type the command the job should execute and press Enter. Optionally repeat the step to provide multiple commands. B. Enter a shell script at the prompt and press Enter after each line in the script. If a script is entered the job uses the shell set in the users SHELL environment the users login shell or /bin/sh whichever is found first. 3. Once finished press Ctrl+D on an empty line to exit the prompt. If the set of commands or the script tries to display information to standard output the output is emailed to the user. To view the list of pending jobs use the atq command. See Section 21.2.5 “Viewing Pending Jobs” for more information. You can also restrict the usage of the batch command. For more information see Section 21.2.7 “Controlling Access to At and Batch” for details. 21.2.5. Viewing Pending Jobs To view the pending At and Batch jobs run the atq command. The atq command displays a list of pending jobs with each job on a separate line. Each line follows the job number date hour job class and user name format. Users can only view their own jobs. If the root user executes the atq command all jobs for all users are displayed. 21.2.6. Additional Command Line Options Additional command line options for at and batch include the following: Table 21.1. at and batch Command Line Options Option Description -f Read the commands or shell script from a file instead of specifying them at the prompt. Syst em Administ rat ors Guide 4 36

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-m Send email to the user when the job has been completed. -v Display the time that the job is executed. Option Description 21.2.7. Controlling Access to At and Batch You can restrict the access to the at and batch commands using the /etc/at.allow and /etc/at.deny files. These access control files use the same format defining one user name on each line. Mind that no whitespace are permitted in either file. If the file at.allow exists only users listed in the file are allowed to use at or batch and the at.deny file is ignored. If at.allow does not exist users listed in at.deny are not allowed to use at or batch. The at daemon atd does not have to be restarted if the access control files are modified. The access control files are read each time a user tries to execute the at or batch commands. The root user can always execute at and batch commands regardless of the content of the access control files. 21.3. Scheduling a Job to Run on Next Boot Using a systemd Unit File The cron anacron at and batch utilities allow scheduling jobs for specific times or for when system workload reaches a certain level. It is also possible to create a job that will run during the next system boot. This is done by creating a systemd unit file that specifies the script to run and its dependencies. To configure a script to run on the next boot: 1. Create the systemd unit file that specifies at which stage of the boot process to run the script. This example shows a unit file with a reasonable set of Wants and After dependencies: cat /etc/systemd/system/one-time.service Unit The script needs to execute after: network interfaces are configured Wantsnetwork-online.target Afternetwork-online.target all remote filesystems NFS/_netdev are mounted Afterremote-fs.target name DNS and user resolution from remote databases AD/LDAP are available Afternss-user-lookup.target nss-lookup.target the system clock has synchronized Aftertime-sync.target Service Typeoneshot ExecStart/usr/local/bin/foobar.sh Install WantedBymulti-user.target If you use this example: ⁠Chapt er 2 1 . Aut omat ing Syst em T asks 4 37

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substitute /usr/local/bin/foobar.sh with the name of your script modify the set of After entries if necessary For information on specifying the stage of boot see Section 9.6 “Creating and Modifying systemd Unit Files”. 2. If you want the systemd service to stay active after executing the script add the RemainAfterExityes line to the Service section: Service Typeoneshot RemainAfterExityes ExecStart/usr/local/bin/foobar.sh 3. Reload the systemd daemon: systemctl daemon-reload 4. Enable the systemd service: systemctl enable one-time.service 5. Create the script to execute: cat /usr/local/bin/foobar.sh /bin/bash touch /root/test_file 6. If you want the script to run during the next boot only and not on every boot add a line that disables the systemd unit: /bin/bash touch /root/test_file systemctl disable one-time.service 7. Make the script executable: chmod +x /usr/local/bin/foobar.sh 21.4. Additional Resources To learn more about configuring automated tasks see the following installed documentation: cron8 man page contains an overview of cron. crontab man pages in sections 1 and 5: The manual page in section 1 contains an overview of the crontab file. The man page in section 5 contains the format for the file and some example entries. Syst em Administ rat ors Guide 4 38

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anacron8 manual page contains an overview of anacron. anacrontab5 manual page contains an overview of the anacrontab file. run-parts4 manual page contains an overview of the run-parts script. /usr/share/doc/at-version/timespec contains detailed information about the time values that can be used in cron job definitions. at manual page contains descriptions of at and batch and their command line options. ⁠Chapt er 2 1 . Aut omat ing Syst em T asks 4 39

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Chapter 22. Automatic Bug Reporting Tool ABRT 22.1. Introduction to ABRT The Automatic Bug Reporting Tool commonly abbreviated as ABRT is a set of tools that is designed to help users detect and report application crashes. Its main purpose is to ease the process of reporting issues and finding solutions. In this context the solution can be a Bugzilla ticket a knowledge-base article or a suggestion to update a package to a version containing a fix. ABRT consists of the abrtd daemon and a number of system services and utilities for processing analyzing and reporting detected problems. The daemon runs silently in the background most of the time and springs into action when an application crashes or a kernel oops is detected. The daemon then collects the relevant problem data such as a core file if there is one the crashing applications command line parameters and other data of forensic utility. ABRT currently supports the detection of crashes in applications written in the C C++ Java Python and Ruby programming languages as well as X.Org crashes kernel oopses and kernel panics. See Section 22.4 “Detecting Software Problems” for more detailed information on the types of failures and crashes supported and the way the various types of crashes are detected. The identified problems can be reported to a remote issue tracker and the reporting can be configured to happen automatically whenever an issue is detected. Problem data can also be stored locally or on a dedicated system and reviewed reported and deleted manually by the user. The reporting tools can send problem data to a Bugzilla database or the Red Hat Technical Support RHTSupport website. The tools can also upload it using FTP or SCP send it as an email or write it to a file. The ABRT component that handles existing problem data as opposed to for example the creation of new problem data is a part of a separate project libreport. The libreport library provides a generic mechanism for analyzing and reporting problems and it is used by applications other than ABRT as well. However ABRT and libreport operation and configuration are closely integrated. They are therefore discussed as one in this document. 22.2. Installing ABRT and Starting its Services In order to use ABRT ensure that the abrt-desktop or the abrt-cli package is installed on your system. The abrt-desktop package provides a graphical user interface for ABRT and the abrt-cli package contains a tool for using ABRT on the command line. You can also install both. The general workflow with both the ABRT GUI and the command line tool is procedurally similar and follows the same pattern. Warning Please note that installing the ABRT packages overwrites the /proc/sys/kernel/core_pattern file which can contain a template used to name core- dump files. The content of this file will be overwritten to: |/usr/libexec/abrt-hook-ccpp s c p u g t e See Section 8.2.4 “Installing Packages” for general information on how to install packages using the Yum package manager. Syst em Administ rat ors Guide 4 4 0

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22.2.1. Installing the ABRT GUI The ABRT graphical user interface provides an easy-to-use front end for working in a desktop environment. You can install the required package by running the following command as the root user: yum install abrt-desktop Upon installation the ABRT notification applet is configured to start automatically when your graphical desktop session starts. You can verify that the ABRT applet is running by issuing the following command in a terminal: ps -el | grep abrt-applet 0 S 500 2036 1824 0 80 0 - 61604 poll_s 00:00:00 abrt- applet If the applet is not running you can start it manually in your current desktop session by running the abrt-applet program: abrt-applet 1 2261 22.2.2. Installing ABRT for the Command Line The command line interface is useful on headless machines remote systems connected over a network or in scripts. You can install the required package by running the following command as the root user: yum install abrt-cli 22.2.3. Installing Supplementary ABRT T ools To receive email notifications about crashes detected by ABRT you need to have the libreport-plugin- mailx package installed. You can install it by executing the following command as root: yum install libreport-plugin-mailx By default it sends notifications to the root user at the local machine. The email destination can be configured in the /etc/libreport/plugins/mailx.conf file. To have notifications displayed in your console at login time install the abrt-console-notification package as well. ABRT can detect analyze and report various types of software failures. By default ABRT is installed with support for the most common types of failures such as crashes of C and C++ applications. Support for other types of failures is provided by independent packages. For example to install support for detecting exceptions in applications written using the Java language run the following command as root: yum install abrt-java-connector ⁠Chapt er 2 2 . Aut omat ic Bug Report ing T ool ABRT 4 4 1

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See Section 22.4 “Detecting Software Problems” for a list of languages and software projects which ABRT supports. The section also includes a list of all corresponding packages that enable the detection of the various types of failures. 22.2.4 . Starting the ABRT Services The abrtd daemon requires the abrt user to exist for file system operations in the /var/spool/abrt directory. When the abrt package is installed it automatically creates the abrt user whose UID and GID is 173 if such user does not already exist. Otherwise the abrt user can be created manually. In that case any UID and GID can be chosen because abrtd does not require a specific UID and GID. The abrtd daemon is configured to start at boot time. You can use the following command to verify its current status: systemctl is-active abrtd.service active If systemctl returns inactive or unknown the daemon is not running. You can start it for the current session by entering the following command as root: systemctl start abrtd.service You can use the same commands to start or check status of related error-detection services. For example make sure the abrt-ccpp service is running if you want ABRT to detect C or C++ crashes. See Section 22.4 “Detecting Software Problems” for a list of all available ABRT detection services and their respective packages. With the exception of the abrt-vmcore and abrt-pstoreoops services which are only started when a kernel panic or kernel oops occurs all ABRT services are automatically enabled and started at boot time when their respective packages are installed. You can disable or enable any ABRT service by using the systemctl utility as described in Chapter 9 Managing Services with systemd. 22.2.5. T esting ABRT Crash Detection To test that ABRT works properly use the kill command to send the SEGV signal to terminate a process. For example start a sleep process and terminate it with the kill command in the following way: sleep 100 1 2823 kill -s SEGV 2823 ABRT detects a crash shortly after executing the kill command and provided a graphical session is running the user is notified of the detected problem by the GUI notification applet. On the command line you can check that the crash was detected by running the abrt-cli list command or by examining the crash dump created in the /var/tmp/abrt/ directory. See Section 22.5 “Handling Detected Problems” for more information on how to work with detected crashes. 22.3. Configuring ABRT A problem life cycle is driven by events in ABRT. For example: Syst em Administ rat ors Guide 4 4 2

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Event 1 — a problem-data directory is created. Event 2 — problem data is analyzed. Event 3 — the problem is reported to Bugzilla. Whenever a problem is detected ABRT compares it with all existing problem data and determines whether that same problem has already been recorded. If it has the existing problem data is updated and the most recent duplicate problem is not recorded again. If the problem is not recognized by ABRT a problem-data directory is created. A problem-data directory typically consists of files such as: analyzer architecture coredump cmdline executable kernel os_release reason time and uid. Other files such as backtrace can be created during the analysis of the problem depending on which analyzer method is used and its configuration settings. Each of these files holds specific information about the system and the problem itself. For example the kernel file records the version of a crashed kernel. After the problem-data directory is created and problem data gathered you can process the problem using either the ABRT GUI or the abrt-cli utility for the command line. See Section 22.5 “Handling Detected Problems” for more information about the ABRT tools provided for working with recorded problems. 22.3.1. Configuring Events ABRT events use plugins to carry out the actual reporting operations. Plugins are compact utilities that the events call to process the content of problem-data directories. Using plugins ABRT is capable of reporting problems to various destinations and almost every reporting destination requires some configuration. For instance Bugzilla requires a username password and a URL pointing to an instance of the Bugzilla service. Some configuration details can have default values such as a Bugzilla URL but others cannot have sensible defaults for example a username. ABRT looks for these settings in configuration files such as report_Bugzilla.conf in the /etc/libreport/events/ or HOME/.cache/abrt/events/ directories for system-wide or user-specific settings respectively. The configuration files contain pairs of directives and values. These files are the bare minimum necessary for running events and processing the problem-data directories. The gnome-abrt and abrt-cli tools read the configuration data from these files and pass it to the events they run. Additional information about events such as their description names types of parameters that can be passed to them as environment variables and other properties is stored in event_name.xml files in the /usr/share/libreport/events/ directory. These files are used by both gnome-abrt and abrt-cli to make the user interface more friendly. Do not edit these files unless you want to modify the standard installation. If you intend to do that copy the file to be modified to the /etc/libreport/events/ directory and modify the new file. These files can contain the following information: a user-friendly event name and description Bugzilla Report to Bugzilla bug tracker a list of items in a problem-data directory that are required for the event to succeed a default and mandatory selection of items to send or not send whether the GUI should prompt for data review what configuration options exist their types string Boolean etc. default value prompt string etc. this lets the GUI build appropriate configuration dialogs. ⁠Chapt er 2 2 . Aut omat ic Bug Report ing T ool ABRT 4 4 3

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For example the report_Logger event accepts an output filename as a parameter. Using the respective event_name.xml file the ABRT GUI determines which parameters can be specified for a selected event and allows the user to set the values for these parameters. The values are saved by the ABRT GUI and reused on subsequent invocations of these events. Note that the ABRT GUI saves configuration options using the GNOME Keyring tool and by passing them to events it overrides data from text configuration files. To open the graphical Configuration window choose Automatic Bug Reporting Tool → Preferences from within a running instance of the gnome-abrt application. This window shows a list of events that can be selected during the reporting process when using the GUI. When you select one of the configurable events you can click the Configure button and modify the settings for that event. Figure 22.1. Configuring ABRT Events Syst em Administ rat ors Guide 4 4 4

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Important All files in the /etc/libreport/ directory hierarchy are world-readable and are meant to be used as global settings. Thus it is not advisable to store usernames passwords or any other sensitive data in them. The per-user settings set in the GUI application and readable by the owner of HOME only are safely stored in GNOME Keyring or they can be stored in a text configuration file in HOME/.abrt/ for use with abrt-cli. The following table shows a selection of the default analyzing collecting and reporting events provided by the standard installation of ABRT. The table lists each events name identifier configuration file from the /etc/libreport/events.d/ directory and a brief description. Note that while the configuration files use the event identifiers the ABRT GUI refers to the individual events using their names. Note also that not all of the events can be set up using the GUI. For information on how to define a custom event see Section 22.3.2 “Creating Custom Events”. Table 22.1. Standard ABRT Events Name Identifier and Configuration File Description uReport report_uReport Uploads a μReport to the FAF server. Mailx report_Mailx mailx_event.conf Sends the problem report via the Mailx utility to a specified email address. Bugzilla report_Bugzilla bugzilla_event.conf Reports the problem to the specifid installation of the Bugz illa bug tracker. Red Hat Customer Support report_RHTSupport rhtsupport_event.conf Reports the problem to the Red Hat Technical Support system. Analyze C or C++ Crash analyze_CCpp ccpp_event.conf Sends the core dump to a remote retrace server for analysis or performs a local analysis if the remote one fails. Report uploader report_Uploader uploader_event.conf Uploads a tarball .tar.gz archive with problem data to the chosen destination using the FTP or the SCP protocol. Analyze VM core analyze_VMcore vmcore_event.conf Runs the GDB the GNU debugger on the problem data of a kernel oops and generates a backtrace of the kernel. Local GNU Debugger analyze_LocalGDB ccpp_event.conf Runs GDB the GNU debugger on the problem data of an application and generates a backtrace of the program. Collect .xsession- errors analyze_xsession_errors ccpp_event.conf Saves relevant lines from the /.xsession- errors file to the problem report. ⁠Chapt er 2 2 . Aut omat ic Bug Report ing T ool ABRT 4 4 5

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Logger report_Logger print_event.conf Creates a problem report and saves it to a specified local file. Kerneloops.org report_Kerneloops koops_event.conf Sends a kernel problem to the oops tracker at kerneloops.org. Name Identifier and Configuration File Description 22.3.2. Creating Custom Events Each event is defined by one rule structure in a respective configuration file. The configuration files are typically stored in the /etc/libreport/events.d/ directory. These configuration files are loaded by the main configuration file /etc/libreport/report_event.conf. There is no need to edit the default configuration files because abrt will run the scripts contained in /etc/libreport/events.d/. This file accepts shell metacharacters etc. and interprets relative paths relatively to its location. Each rule starts with a line with a non-space leading character and all subsequent lines starting with the space character or the tab character are considered a part of this rule. Each rule consists of two parts a condition part and a program part. The condition part contains conditions in one of the following forms: VARVAL VARVAL VALREGEX where: VAR is either the EVENT key word or a name of a problem-data directory element such as executable package hostname etc. VAL is either a name of an event or a problem-data element and REGEX is a regular expression. The program part consists of program names and shell-interpretable code. If all conditions in the condition part are valid the program part is run in the shell. The following is an event example: EVENTpost-create date /tmp/dt echo HOSTNAME `uname -r` This event would overwrite the contents of the /tmp/dt file with the current date and time and print the host name of the machine and its kernel version on the standard output. Here is an example of a more complex event which is actually one of the predefined events. It saves relevant lines from the /.xsession-errors file to the problem report of any problem for which the abrt-ccpp service has been used provided the crashed application had any X11 libraries loaded at the time of the crash: EVENTanalyze_xsession_errors analyzerCCpp dso_list./libX11. test -f /.xsession-errors || echo "No /.xsession-errors" exit 1 Syst em Administ rat ors Guide 4 4 6

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test -r /.xsession-errors || echo "Cant read /.xsession- errors" exit 1 executable`cat executable` base_executableexecutable/ grep -F -e "base_executable" /.xsession-errors | tail -999 xsession_errors echo "Element xsession_errors saved" The set of possible events is not definitive. System administrators can add events according to their need in the /etc/libreport/events.d/ directory. Currently the following event names are provided with the standard ABRT and libreport installations: post-create This event is run by abrtd to process newly created problem-data directories. When the post-create event is run abrtd checks whether the new problem data matches any of the already existing problem directories. If such a problem directory exists it is updated and the new problem data is discarded. Note that if the script in any definition of the post-create event exits with a non-zero value abrtd will terminate the process and will drop the problem data. notify notify-dup The notify event is run following the completion of post-create. When the event is run the user can be sure that the problem deserves their attention. The notify-dup is similar except it is used for duplicate occurrences of the same problem. analyze_name_suffix where name_suffix is the replaceable part of the event name. This event is used to process collected data. For example the analyze_LocalGDB event uses the GNU Debugger GDB utility to process the core dump of an application and produce a backtrace of the crash. collect_name_suffix …where name_suffix is the adjustable part of the event name. This event is used to collect additional information on problems. report_name_suffix …where name_suffix is the adjustable part of the event name. This event is used to report a problem. 22.3.3. Setting Up Automatic Reporting ABRT can be configured to send initial anonymous reports or μReports of any detected issues or crashes automatically without any user interaction. When automatic reporting is turned on the so called μReport which is normally sent at the beginning of the crash-reporting process is sent immediately after a crash is detected. This prevents duplicate support cases based on identical crashes. To enable the autoreporting feature issue the following command as root: abrt-auto-reporting enabled The above command sets the AutoreportingEnabled directive in the /etc/abrt/abrt.conf configuration file to yes. This system-wide setting applies to all users of the system. Note that by ⁠Chapt er 2 2 . Aut omat ic Bug Report ing T ool ABRT 4 4 7

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enabling this option automatic reporting will also be enabled in the graphical desktop environment. To only enable autoreporting in the ABRT GUI switch the Automatically send uReport option to YES in the Problem Reporting Configuration window. To open this window choose Automatic Bug Reporting Tool → ABRT Configuration from within a running instance of the gnome-abrt application. To launch the application go to Applications → Sundry → Automatic Bug Reporting Tool. Figure 22.2. Configuring ABRT Problem Reporting Upon detection of a crash by default ABRT submits a μReport with basic information about the problem to Red Hats ABRT server. The server determines whether the problem is known and either provides a short description of the problem along with a URL of the reported case if known or invites the user to report it if not known. Syst em Administ rat ors Guide 4 4 8

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Note A μReport microreport is a JSON object representing a problem such as a binary crash or a kernel oops. These reports are designed to be brief machine readable and completely anonymous which is why they can be used for automated reporting. The μReports make it possible to keep track of bug occurrences but they usually do not provide enough information for engineers to fix the bug. A full bug report is needed for a support case to be opened. To change the default behavior of the autoreporting facility from sending a μReport modify the value of the AutoreportingEvent directive in the /etc/abrt/abrt.conf configuration file to point to a different ABRT event. See Table 22.1 “Standard ABRT Events” for an overview of the standard events. 22.4. Detecting Software Problems ABRT is capable of detecting analyzing and processing crashes in applications written in a variety of different programming languages. Many of the packages that contain the support for detecting the various types of crashes are installed automatically when either one of the main ABRT packages abrt-desktop abrt-cli is installed. See Section 22.2 “Installing ABRT and Starting its Services” for instructions on how to install ABRT. See the table below for a list of the supported types of crashes and the respective packages. Table 22.2. Supported Programming Languages and Software Projects Langauge/Project Package C or C++ abrt-addon-ccpp Python abrt-addon-python Ruby rubygem-abrt Java abrt-java-connector X.Org abrt-addon-xorg Linux kernel oops abrt-addon-kerneloops Linux kernel panic abrt-addon-vmcore Linux persistent storage abrt-addon-pstoreoops 22.4 .1. Detecting C and C++ Crashes The abrt-ccpp service installs its own core-dump handler which when started overrides the default value of the kernels core_pattern variable so that C and C++ crashes are handled by abrtd. If you stop the abrt-ccpp service the previously specified value of core_pattern is reinstated. By default the /proc/sys/kernel/core_pattern file contains the string core which means that the kernel produces files with the core. prefix in the current directory of the crashed process. The abrt-ccpp service overwrites the core_pattern file to contain the following command: |/usr/libexec/abrt-hook-ccpp s c p u g t e This command instructs the kernel to pipe the core dump to the abrt-hook-ccpp program which stores it in ABRTs dump location and notifies the abrtd daemon of the new crash. It also stores the following files from the /proc/PID/ directory where PID is the ID of the crashed process for ⁠Chapt er 2 2 . Aut omat ic Bug Report ing T ool ABRT 4 4 9

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debugging purposes: maps limits cgroup status. See proc5 for a description of the format and the meaning of these files. 22.4 .2. Detecting Python Exceptions The abrt-addon-python package installs a custom exception handler for Python applications. The Python interpreter then automatically imports the abrt.pth file installed in /usr/lib64/python2.7/site-packages/ which in turn imports abrt_exception_handler.py. This overrides Pythons default sys.excepthook with a custom handler which forwards unhandled exceptions to abrtd via its Socket API. To disable the automatic import of site-specific modules and thus prevent the ABRT custom exception handler from being used when running a Python application pass the -S option to the Python interpreter: python -S file.py In the above command replace file.py with the name of the Python script you want to execute without the use of site-specific modules. 22.4 .3. Detecting Ruby Exceptions The rubygem-abrt package registers a custom handler using the at_exit feature which is executed when a program ends. This allows for checking for possible unhandled exceptions. Every time an unhandled exception is captured the ABRT handler prepares a bug report which can be submitted to Red Hat Bugzilla using standard ABRT tools. 22.4 .4 . Detecting Java Exceptions The ABRT Java Connector is a JVM agent that reports uncaught Java exceptions to abrtd. The agent registers several JVMTI event callbacks and has to be loaded into the JVM using the - agentlib command line parameter. Note that the processing of the registered callbacks negatively impacts the performance of the application. Use the following command to have ABRT catch exceptions from a Java class: java -agentlib:abrt-java-connectorabrton MyClass - platform.jvmtiSupported true In the above command replace MyClass with the name of the Java class you want to test. By passing the abrton option to the connector you ensure that the exceptions are handled by abrtd. In case you want to have the connector output the exceptions to standard output omit this option. 22.4 .5. Detecting X.Org Crashes The abrt-xorg service collects and processes information about crashes of the X.Org server from the /var/log/Xorg.0.log file. Note that no report is generated if a blacklisted X.org module is loaded. Instead a not-reportable file is created in the problem-data directory with an appropriate explanation. You can find the list of offending modules in the /etc/abrt/plugins/xorg.conf file. Only proprietary graphics-driver modules are blacklisted by default. 22.4 .6. Detecting Kernel Oopses and Panics By checking the output of kernel logs ABRT is able to catch and process the so-called kernel oopses — non-fatal deviations from the correct behavior of the Linux kernel. This functionality is Syst em Administ rat ors Guide 4 50

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provided by the abrt-oops service. ABRT can also detect and process kernel panics — fatal non-recoverable errors that require a reboot using the abrt-vmcore service. The service only starts when a vmcore file a kernel-core dump appears in the /var/crash/ directory. When a core-dump file is found abrt-vmcore creates a new problem-data directory in the /var/tmp/abrt/ directory and moves the core- dump file to the newly created problem-data directory. After the /var/crash/ directory is searched the service is stopped. For ABRT to be able to detect a kernel panic the kdump service must be enabled on the system. The amount of memory that is reserved for the kdump kernel has to be set correctly. You can set it using the system-config-kdump graphical tool or by specifying the crashkernel parameter in the list of kernel options in the GRUB menu. For details on how to enable and configure kdump see the Red Hat Enterprise Linux 7 Kernel Crash Dump Guide. For information on making changes to the GRUB menu see Chapter 24 Working with the GRUB 2 Boot Loader. Using the abrt-pstoreoops service ABRT is capable of collecting and processing information about kernel panics which on systems that support pstore is stored in the automatically-mounted /sys/fs/pstore/ directory. The platform-dependent pstore interface persistent storage provides a mechanism for storing data across system reboots thus allowing for preserving kernel panic information. The service starts automatically when kernel crash-dump files appear in the /sys/fs/pstore/ directory. 22.5. Handling Detected Problems Problem data saved by abrtd can be viewed reported and deleted using either the command line tool abrt-cli or the graphical tool gnome-abrt. Note Note that ABRT identifies duplicate problems by comparing new problems with all locally saved problems. For a repeating crash ABRT requires you to act upon it only once. However if you delete the crash dump of that problem the next time this specific problem occurs ABRT will treat it as a new crash: ABRT will alert you about it prompt you to fill in a description and report it. To avoid having ABRT notifying you about a recurring problem do not delete its problem data. 22.5.1. Using the Command Line T ool In the command line environment the user is notified of new crashes on login provided they have the abrt-console-notification package installed. The console notification looks like the following: ABRT has detected 1 problems. For more info run: abrt-cli list --since 1398783164 To view detected problems enter the abrt-cli list command: abrt-cli list id 6734c6f1a1ed169500a7bfc8bd62aabaf039f9aa Directory: /var/tmp/abrt/ccpp-2014-04-21-09:47:51-3430 count: 1 executable: /usr/bin/sleep ⁠Chapt er 2 2 . Aut omat ic Bug Report ing T ool ABRT 4 51

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package: coreutils-8.22-11.el7 time: Mon 21 Apr 2014 09:47:51 AM EDT uid: 1000 Run abrt-cli report /var/tmp/abrt/ccpp-2014-04-21-09:47:51-3430 for creating a case in Red Hat Customer Portal Each crash listed in the output of the abrt-cli list command has a unique identifier and a directory that can be used for further manipulation using abrt-cli. To view information about just one particular problem use the abrt-cli info command: abrt-cli info -d directory_or_id To increase the amount of information displayed when using both the list and info sub- commands pass them the -d --detailed option which shows all stored information about the problems listed including respective backtrace files if they have already been generated. To analyze and report a certain problem use the abrt-cli report command: abrt-cli report directory_or_id Upon invocation of the above command you will be asked to provide your credentials for opening a support case with Red Hat Customer Support. Next abrt-cli opens a text editor with the content of the report. You can see what is being reported and you can fill in instructions on how to reproduce the crash and other comments. You should also check the backtrace because the backtrace might be sent to a public server and viewed by anyone depending on the problem-reporter event settings. Note You can choose which text editor is used to check the reports. abrt-cli uses the editor defined in the ABRT_EDITOR environment variable. If the variable is not defined it checks the VISUAL and EDITOR variables. If none of these variables is set the vi editor is used. You can set the preferred editor in your .bashrc configuration file. For example if you prefer GNU Emacs add the following line to the file: export VISUALemacs When you are done with the report save your changes and close the editor. If you have reported your problem to the Red Hat Customer Support database a problem case is filed in the database. From now on you will be informed about the problem-resolution progress via email you provided during the process of reporting. You can also monitor the problem case using the URL that is provided to you when the problem case is created or via emails received from Red Hat Support. If you are certain that you do not want to report a particular problem you can delete it. To delete a problem so that ABRT does not keep information about it use the command: abrt-cli rm directory_or_id To display help about a particular abrt-cli command use the --help option: abrt-cli command --help Syst em Administ rat ors Guide 4 52

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22.5.2. Using the GUI The ABRT daemon broadcasts a D-Bus message whenever a problem report is created. If the ABRT applet is running in a graphical desktop environment it catches this message and displays a notification dialog on the desktop. You can open the ABRT GUI using this dialog by clicking on the Report button. You can also open the ABRT GUI by selecting the Applications → Sundry → Automatic Bug Reporting Tool menu item. Alternatively you can run the ABRT GUI from the command line as follows: gnome-abrt The ABRT GUI window displays a list of detected problems. Each problem entry consists of the name of the failing application the reason why the application crashed and the date of the last occurrence of the problem. Figure 22.3. ABRT GUI To access a detailed problem description double-click on a problem-report line or click on the Report button while the respective problem line is selected. You can then follow the instructions to proceed with the process of describing the problem determining how it should be analyzed and where it should be reported. To discard a problem click on the Delete button. 22.6. Additional Resources For more information about ABRT and related topics see the resources listed below. Installed Documentation abrtd8 — The manual page for the abrtd daemon provides information about options that can be used with the daemon. abrt_event.conf5 — The manual page for the abrt_event.conf configuration file describes the format of its directives and rules and provides reference information about event meta-data configuration in XML files. ⁠Chapt er 2 2 . Aut omat ic Bug Report ing T ool ABRT 4 53

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Online Documentation Red Hat Enterprise Linux 7 Networking Guide — The Networking Guide for Red Hat Enterprise Linux 7 documents relevant information regarding the configuration and administration of network interfaces and network services on this system. Red Hat Enterprise Linux 7 Kernel Crash Dump Guide — The Kernel Crash Dump Guide for Red Hat Enterprise Linux 7 documents how to configure test and use the kdump crash recovery service and provides a brief overview of how to analyze the resulting core dump using the crash debugging utility. See Also Chapter 20 Viewing and Managing Log Files describes the configuration of the rsyslog daemon and the systemd journal and explains how to locate view and monitor system logs. Chapter 8 Yum describes how to use the Yum package manager to search install update and uninstall packages on the command line. Chapter 9 Managing Services with systemd provides an introduction to systemd and documents how to use the systemctl command to manage system services configure systemd targets and execute power management commands. Syst em Administ rat ors Guide 4 54

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Chapter 23. OProfile OProfile is a low overhead system-wide performance monitoring tool. It uses the performance monitoring hardware on the processor to retrieve information about the kernel and executables on the system such as when memory is referenced the number of L2 cache requests and the number of hardware interrupts received. On a Red Hat Enterprise Linux system the oprofile package must be installed to use this tool. Many processors include dedicated performance monitoring hardware. This hardware makes it possible to detect when certain events happen such as the requested data not being in cache. The hardware normally takes the form of one or more counters that are incremented each time an event takes place. When the counter value increments an interrupt is generated making it possible to control the amount of detail and therefore overhead produced by performance monitoring. OProfile uses this hardware or a timer-based substitute in cases where performance monitoring hardware is not present to collect samples of performance-related data each time a counter generates an interrupt. These samples are periodically written out to disk later the data contained in these samples can then be used to generate reports on system-level and application-level performance. Be aware of the following limitations when using OProfile: Use of shared libraries — Samples for code in shared libraries are not attributed to the particular application unless the --separatelibrary option is used. Performance monitoring samples are inexact — When a performance monitoring register triggers a sample the interrupt handling is not precise like a divide by zero exception. Due to the out-of- order execution of instructions by the processor the sample may be recorded on a nearby instruction. opreport does not associate samples for inline functions properly — opreport uses a simple address range mechanism to determine which function an address is in. Inline function samples are not attributed to the inline function but rather to the function the inline function was inserted into. OProfile accumulates data from multiple runs — OProfile is a system-wide profiler and expects processes to start up and shut down multiple times. Thus samples from multiple runs accumulate. Use the command opcontrol --reset to clear out the samples from previous runs. Hardware performance counters do not work on guest virtual machines — Because the hardware performance counters are not available on virtual systems you need to use the timer mode. Enter the command opcontrol --deinit and then execute modprobe oprofile timer1 to enable the timer mode. Non-CPU-limited performance problems — OProfile is oriented to finding problems with CPU-limited processes. OProfile does not identify processes that are asleep because they are waiting on locks or for some other event to occur for example an I/O device to finish an operation. 23.1. Overview of Tools Table 23.1 “OProfile Commands” provides a brief overview of the most commonly used tools provided with the oprofile package. Table 23.1. OProfile Commands ⁠Chapt er 2 3. OProfile 4 55

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Command Description ophelp Displays available events for the systems processor along with a brief description of each. opimport Converts sample database files from a foreign binary format to the native format for the system. Only use this option when analyzing a sample database from a different architecture. opannotate Creates annotated source for an executable if the application was compiled with debugging symbols. See Section 23.6.4 “Using opannotate” for details. opcontrol Configures what data is collected. See Section 23.3 “Configuring OProfile Using Legacy Mode” for details. operf Recommended tool to be used in place of opcontrol for profiling. See Section 23.2 “Using operf” for details. For differences between operf and opcontrol see Section 23.1.1 “operf vs. opcontrol”. opreport Retrieves profile data. See Section 23.6.1 “Using opreport” for details. oprofiled Runs as a daemon to periodically write sample data to disk. 23.1.1. operf vs. opcontrol There are two mutually exclusive methods for collecting profiling data with OProfile. You can either use the newer and preferred operf or the opcontrol tool. o perf This is the recommended mode for profiling. The operf tool uses the Linux Performance Events Subsystem and therefore does not require the oprofile kernel driver. The operf tool allows you to target your profiling more precisely as a single process or system-wide and also allows OProfile to co-exist better with other tools using the performance monitoring hardware on your system. Unlike opcontrol it can be used without the root privileges. However operf is also capable of system- wide operations with use of the --system-wide option where root authority is required. With operf there is no initial setup needed. You can invoke operf with command-line options to specify your profiling settings. After that you can run the OProfile post-processing tools described in Section 23.6 “Analyzing the Data”. See Section 23.2 “Using operf” for further information. o pco nt ro l This mode consists of the opcontrol shell script the oprofiled daemon and several post- processing tools. The opcontrol command is used for configuring starting and stopping a profiling session. An OProfile kernel driver usually built as a kernel module is used for collecting samples which are then recorded into sample files by oprofiled. You can use legacy mode only if you have root privileges. In certain cases such as when you need to sample areas with disabled interrupt request IRQ this is a better alternative. Before OProfile can be run in legacy mode it must be configured as shown in Section 23.3 “Configuring OProfile Using Legacy Mode”. These settings are then applied when starting OProfile Section 23.4 “Starting and Stopping OProfile Using Legacy Mode”. 23.2. Using operf Syst em Administ rat ors Guide 4 56

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operf is the recommended profiling mode that does not require initial setup before starting. All settings are specified as command-line options and there is no separate command to start the profiling process. To stop operf press Ctrl+C. The typical operf command syntax looks as follows: operf options range command args Replace options with the desired command-line options to specify your profiling settings. Full set of options is described in operf1 manual page. Replace range with one of the following: --system-wide - this setting allows for global profiling see Note --pidPID - this is to profile a running application where PID is the process ID of the process you want to profile. With command and args you can define a specific command or application to be profiled and also the input arguments that this command or application requires. Either command --pid or -- system-wide is required but these cannot be used simultaneously. When you invoke operf on a command line without setting the range option data will be collected for the children processes. Note To run operf --system-wide you need root authority. When finished profiling you can stop operf with Ctrl+C. If you run operf --system-wide as a background process with stop it in a controlled manner in order to process the collected profile data. For this purpose use: kill -SIGINT operf-PID When running operf --system-wide it is recommended that your current working directory is /root or a subdirectory of /root so that sample data files are not stored in locations accessible by regular users. 23.2.1. Specifying the Kernel To monitor the kernel execute the following command: operf --vmlinuxvmlinux_path With this option you can specify a path to a vmlinux file that matches the running kernel. Kernel samples will be attributed to this binary allowing post-processing tools to attribute samples to the appropriate kernel symbols. If this option is not specified all kernel samples will be attributed to a pseudo binary named "no-vmlinux". 23.2.2. Setting Events to Monitor Most processors contain counters which are used by OProfile to monitor specific events. As shown in Table 23.3 “OProfile Processors and Counters” the number of counters available depends on the processor. ⁠Chapt er 2 3. OProfile 4 57

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The events for each counter can be configured via the command line or with a graphical interface. For more information on the graphical interface see Section 23.10 “Graphical Interface”. If the counter cannot be set to a specific event an error message is displayed. Note Some older processor models are not supported by the underlying Linux Performance Events Subsystem kernel and therefore are not supported by operf. If you receive this message: Your kernels Performance Events Subsystem does not support your processor type when attempting to use operf try profiling with opcontrol to see if your processor type may be supported by OProfiles legacy mode. Note Since hardware performance counters are not available on guest virtual machines you have to enable timer mode to use operf on virtual systems. To do so type as root: opcontrol --deinit modprobe oprofile timer1 To set the event for each configurable counter via the command line use: operf --eventsevent1event2… Here pass a comma-separated list of event specifications for profiling. Each event specification is a colon-separated list of attributes in the following form: event-name:sample-rate:unit-mask:kernel:user Table 23.2 “Event Specifications” summarizes these options. The last three values are optional if you omit them they will be set to their default values. Note that certain events do require a unit mask. Table 23.2. Event Specifications Specification Description event-name The exact symbolic event name taken from ophelp Syst em Administ rat ors Guide 4 58

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sample-rate The number of events to wait before sampling again. The smaller the count the more frequent the samples. For events that do not happen frequently a lower count may be needed to capture a statistically significant number of event instances. On the other hand sampling too frequently can overload the system. By default OProfile uses a time-based event set which creates a sample every 100000 clock cycles per processor. unit-mask Unit masks which further define the event are listed in ophelp. You can insert either a hexadecimal value beginning with "0x" or a string that matches the first word of the unit mask description in ophelp. Definition by name is valid only for unit masks having "extra:" parameters as shown by the output of ophelp. This type of unit mask cannot be defined with a hexadecimal value. Note that on certain architectures there can be multiple unit masks with the same hexadecimal value. In that case they have to be specified by their names only. kernel Specifies whether to profile kernel code insert 0 or 1 default user Specifies whether to profile user-space code insert 0 or 1 default Specification Description The events available vary depending on the processor type. When no event specification is given the default event for the running processor type will be used for profiling. See Table 23.4 “Default Events” for a list of these default events. To determine the events available for profiling use the ophelp command. ophelp 23.2.3. Categorization of Samples The --separate-thread option categorizes samples by thread group ID tgid and thread ID tid. This is useful for seeing per-thread samples in multi-threaded applications. When used in conjunction with the --system-wide option --separate-thread is also useful for seeing per- process per-thread group samples for the case where multiple processes are executing the same program during a profiling run. The --separate-cpu option categorizes samples by CPU. 23.3. Configuring OProfile Using Legacy Mode Before OProfile can be run in legacy mode it must be configured. At a minimum selecting to monitor the kernel or selecting not to monitor the kernel is required. The following sections describe how to use the opcontrol utility to configure OProfile. As the opcontrol commands are executed the setup options are saved to the /root/.oprofile/daemonrc file. 23.3.1. Specifying the Kernel ⁠Chapt er 2 3. OProfile 4 59

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First configure whether OProfile should monitor the kernel. This is the only configuration option that is required before starting OProfile. All others are optional. To monitor the kernel execute the following command as root: opcontrol --setup --vmlinux/usr/lib/debug/lib/modules/`uname - r`/vmlinux Important In order to monitor the kernel the kernel-debuginfo package which contains the uncompressed kernel must be installed. For more information on how to install this package see the How to download debuginfo packages like kernel-debuginfo article on the Red Hat Customer Portal. To configure OProfile not to monitor the kernel execute the following command as root: opcontrol --setup --no-vmlinux This command also loads the oprofile kernel module if it is not already loaded and creates the /dev/oprofile/ directory if it does not already exist. See Section 23.7 “Understanding the /dev/oprofile/ directory” for details about this directory. Setting whether samples should be collected within the kernel only c