systemd: What to Know and How to Transition

Transcription

1 systemd: What to Know and How to Transition Tom Sorensen Solutions Architect, Red Hat 2

2 Agenda 4 What is systemd? What does systemd offer? How does this affect me? How do I transition to systemd? What s the next step?

3 What is systemd? 5

4 What is systemd? systemd is a suite of system management daemons, libraries, and utilities designed as a central management and configuration platform for the Linux computer operating system. - From 6

5 *YAWN* 7

6 What is systemd? Replaces init literally 9 init is now a symlink to systemd First process to start and last to stop Parent process of all other processes Manages services and other resources

7 But I liked init... init is really, really old systemd adopted across all major Linux versions 10 Default in Fedora 15 as of May 2011 Slackware in the enterprise anyone?

8 What does systemd offer? 11

9 What does systemd offer? Controls More than Services Dependency Control Service Activation Faster Start Up and Shutdown Improved Resource Management Tracks and Restarts Services Improved Logging, Debugging and Profiling Plenty More... 12

10 Units Controls more than services, it controls all resources on the system - referred to as units. Examples of Units: Services Sockets Targets and more.. Units are defined using Unit Files Naming convention is name.unit_type 13

11 Dependencies Since systemd controls more than services, it can also more intelligently handle dependencies. Define order and requirements for each unit Example: nfs-lock.service Requires=rpcbind.service network.target After=network.target named.service rpcbind.service Before=remote-fs-pre.target 14 No more semi-arbitrary ASCII order loading

12 Common Unit File Options Description=Unit description Documentation=Documentation links Requires=Additional units required Before/After=Unit must start Before/After Wants=Weaker Requires Conflicts=Units cannot co-exist WantedBy/RequiredBy=Set other units requirement 15 Lots of great detail in the RHEL 7 System Administrator's Guide

13 Service Activation With dependency control for all resources, systemd can also activate services on demand. Start up services when needed Save resources Increased reliability Transparent to client Activation by Socket, Device, Path, Bus, and Timer Recommended to convert xinetd services to units 16

14 Parallel, Not Serial With defined dependencies we don t need to wait for other services, sockets, file systems, etc that aren t needed for that specific unit. Allows for Faster Start Up and Shutdown Why does this matter? 17 Downtime matters Five 9 s = 5.26 minutes per year Cloud - Charges by runtime Capacity on demand

15 Improved Resource Management Services are labeled with individual cgroups, including all components and children. Resources are also divided into Slices. Services labeled and isolated with Cgroups More control than nice alone Can configure multiple instances for a single service Can balance by shares or by hard limits 18

16 Kill/Restart Cleanly With each service being tracked by individual cgroup, systemd has an understanding of all related processes. Tracked in the kernel Knows all children 19 Don t need to rely on a potentially misbehaving process to hopefully kill its children

17 Auto-Restarting With more control over the whole service chain, systemd can track the state of all services and make corrections with less impact. It s paying attention! Reality: software does crash occasionally Reduces need for manual intervention Socket stays open, only lose that single transaction 20

18 Improved Logging Every service logs, from when the initial RAM disk is loaded to start the kernel to final shutdown of the system, from all channels. Don t need to wait for syslog to start No More Losing STDERR and STDOUT More detail than classic syslog alone Improved debugging and profiling 21

19 (This is the end of the overview, we ll now get to the practical.) 22

20 How does this affect me? 23

21 How does this affect me? File Locations Targets vs Runlevels Booting with systemd Analyzing the Boot Process Resetting the Root Password Systemctl and Other Commands Logging and journalctl 24

22 File Locations Maintainer files: /usr/lib/systemd/system/ Administrator files: /etc/systemd/system/ Drop-in configs: /etc/systemd/system/<name.unit>.d/ Non-persistent, runtime data: /run/systemd/ Systemd journal, non-persistent: /run/log/journal Note: unit files under /etc will take precedence over /usr 25

23 Targets are the new Runlevels Targets are logical groupings of services and other units that are started and stopped together. Targets!= Runlevels some equivalency 26 Traditional Runlevel Equivalent Target Symlink Target Runlevel 0 poweroff.target runlevel0.target Runlevel 1 rescue.target runlevel1.target Runlevel 2 multi-user.target runlevel2.target Runlevel 3 multi-user.target runlevel3.target Runlevel 4 multi-user.target runlevel4.target Runlevel 5 graphical.target runlevel5.target Runlevel 6 reboot.target runlevel6.target Targets can and will contain other targets

24 Common Targets Common targets are similar to traditional runlevels. 27 Target Purpose graphical.target Supports multiple users, graphical and text-based logins multi-user.target Supports multiple users, text-based logins only rescue.target Single user, local file systems mounted and basic system initialization completed, networking is not activated emergency.target Single user, root file system is mounted read-only, only a few essential services are started, networking is not activated Rescue and Emergency require root password!

25 Working with Targets Viewing the default target: Setting default target: Default target is just a symlink: 28

26 Working with Targets Changing currently loaded target: Changing to rescue mode: Changing to emergency mode without sending message: 29

27 Working with Targets View list of currently loaded targets: Results pipe to less by default: (can use no-pager) 30 Not a single runlevel, but a a collection of targets

28 Shutting Down, Suspending, Etc. Old Command New Command Description halt systemctl halt Halts the system 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 31

29 Boot Process Quick Review BIOS/UEFI Bootloader Kernel and Initrd System Initialization 32

30 Boot Process Boot path determined by default.target Let s track it backwards! 33

31 Boot Process We see graphical.target requires multi-user.target and should start after it. Let s look at multi-user.target... Next, we see multi-user.target requires basic.target... 34

32 Boot Process Which requires basic.target... Which requires sysinit.target... No more requires, but still some wants... 35

33 Boot Process Which wants local-fs-pre.target and swap.target... Once we look in these we see we ve reached the end of the line! 36

34 Boot Process Once systemd has the beginning of the chain, it starts processing at the earliest step, starting all of the associated units in the specified order. But, how does this work for starting individual services? 37

35 Boot Process Services/Units Each target may also have a wants directory in addition to the specific Wants and Requires directives in the unit files. Target Wants Directories: /usr/lib/systemd/system/<name>.target.wants/ /etc/systemd/system/<name>.target.wants/ 38 Files are symlinks to actual unit files

36 Boot Process - Services/Units Example for multi-user.target.wants: 39 /usr/lib are static units for the OS, /etc are system specific

37 Analyzing Boot Process Each unit is tracked during start up Can see what is taking the longest to start at boot 40

38 Analyzing Boot Process 41 Analysis data can also be exported as SVG

39 Resetting Root Password With the change from runlevels to targets, we also have a change to the traditional single user mode. Rescue and emergency targets require root password Let s not learn this at 3am during a fire! Resetting the Root Password of RHEL-7 / systemd 42

40 Resetting Root Password Step 1: Reboot your system Step 2: When the GRUB2 boot loader menu appears, press any key to interrupt, and press e to edit selection 43

41 Resetting Root Password Step 3: Using the cursor keys, navigate to the end of the line that starts with linux16 Step 4: Append rd.break to the end of the line and press Ctrl-X to boot modified config 44

42 Resetting Root Password Step 6: At the switch_root prompt, remount the /sysroot file system read-write, then use chroot to enter the jail Step 7: Reset the root password with passwd 45

43 Resetting Root Password IMPORTANT! (Because you re using SELinux, right?) Step 8: Instruct SELinux to relabel all files upon reboot. System may not boot properly if skipped! Step 9: Exit twice to initiate relabel and reboot NOTE: The relabel may take quite a while to run before the system becomes available. 46

44 systemctl vs service Start, status, stop a service: 47

45 systemctl vs service Note the different order of command option service instead of command service option. This allows you to run systemctl against multiple services at once. Systemsctl start/stop will be silent unless there is an error, in which case it will print to screen and log. 48

46 systemctl vs service List services: 49

47 systemctl vs chkconfig Enable, check, disable a service: 50 --list is not as important because you can see this in status

48 systemctl vs chkconfig List all services: 51

49 systemctl List all services by target as a dependency tree: 52

50 systemctl Lots of options... 53

51 systemd-cgtop Show top control groups by their resource usage: 54 May need to enable accounting perfect drop-in!

52 systemd-cgls Recursively show control group contents: 55

53 systemd-* Lots of new options... 56

54 journalctl View basic logs: Time stamps converted to system local time zone All logged data is shown, including rotated logs Non-persistent by default, can be preserved 57

55 journalctl View most recent logs: (-f to follow) 59 Can force stdout/stderr to write to journal with systemd-cat if wanted

56 journalctl Specify form: 60 Other options:

57 journalctl Filter by priority: Filter by time and priority: 61 Advanced filtering by field, UID, unit, etc..

58 Systemd Journal How to enable persistent logging for the systemd journal System Administrator's Guide prise_linux/7/html/system_administrators_guide/s1-using_the _Journal.html Lennart Poettering - The systemd Journal 62

59 The future is not so future any more... (RHEL 7 is here and systemd is part of every major Linux distro. It s time to start using it.) 63

60 How do I transition to systemd? 64

61 How do I transition? Start using the new commands Learn more about cgroups Convert your init scripts Drop-in config overrides Benefit from auto-restart Address rc.local Convert xinetd 65

62 Start using the new commands Bash Completion is your friend! # yum install bash-completion service chkconfig systemd Cheat Sheet for Red Hat Enterprise Linux 7 Common Administrative Commands in RHEL 5, 6, &

63 Embrace cgroups Already available in RHEL 6 More easily controlled in RHEL 7 Resource Management and Linux Containers Guide e_linux/7/html/resource_management_and_linux_containers_guide/i ndex.html 67

64 Convert your init scripts How to convert init scripts to systemd units files Step 1: Check out your simple init script 68

65 Convert your init scripts Step 1, continued... 69

66 Convert your init scripts Step 1, continued a bit more... 70

67 Convert your init scripts Step 2: Modify/Install your RHEL 6 package on your RHEL 7 system and ensure it works with a manual start Step 3: Create a unit file on the RHEL 7 system 71

68 Convert your init scripts Step 4: Notify systemd of the new unit file Step 5: Start the service and verify it is running 72

69 Convert your init scripts Step 6: Enabled the service to start on boot once you ve verified it s functioning as expected Step 7: Profit! 73

70 Drop-in Config Overrides Drop-in configs allows you to override only specific directives without overriding the entire unit file. If you just copy the maintainer file from /usr/lib into /etc and make changes your system will use only the directives in that /etc unit file. This means that if the maintainers improve or change something in the default unit file your system will not ever see the new changes. 74

71 Drop-in Config Overrides Step 1: Create /etc/systemd/system/<name.unit>.d/ directory Step 2: Create a file containing only the directives you d like to modify Step 3: Reload systemd (systemd will warn you in status) 75

72 Drop-in Config Overrides Step 4: Restart your service and check the new status 76

73 Auto-Restarting Processes SSHD configured to auto-restart by default 77 If main process dies, it will restart after 42 seconds

74 Using rc.local rc.local is supported, but no longer runs last 78 chmod +x /etc/rc.d/rc.local Just a service - /usr/lib/systemd/system/rc-local.service

75 Convert xinetd Example: Converting SSHD to Run On-Demand Stolen from: Step 1: Create an file like the following example 79 Note after the sshd, this marks it as an instance

76 Convert xinetd Step 2: Disable sshd.service Step 3: Enable sshd.socket 80 Probably a good idea to make sure you have non-ssh access to this machine as well. ;)

77 Convert xinetd Step 4: Stop sshd.service and start sshd.socket Step 5: Reconnect with SSH and check the new connection 81

78 Reaching Maximum Capacity! 82

79 Review: systemd Replaces init and does much more It is here and it s powerful New boot and root password reset process New commands and functionality Plenty of great information and resources available 83

80 What s the next step? 84

81 Continue planning your transition Define your goals Is it time to embrace SELinux? Continue your research RHEL 7 Migration Planning Guide rprise_linux/7/html/migration_planning_guide/ Navigating Red Hat Enterprise Linux Talk to your TAM and SA!

82 Learn More Lots of great info at and Overview of systemd for RHEL 7 Red Hat Summit Getting Ready for systemd RHEL 7 - systemd Service & Resource Management Rethinking PID 1 by Lennart Poettering 86

83 Learn More not just Red Hat! Arch Wiki Arch Why We Switched Gentoo Documentation OpenSUSE, Debian, Ubuntu also on or transitioning to systemd 87

84 Thank you! 88