今更聞けないsystemd - Now Beginning Systemd

builderscon tokyo 2019

Transcript

1. Now Beginning Systemd @nasa9084
2. $ whoami • @nasa9084 • LINE Corp. • Go / Kubernetes Engineer
3. systemd
4. What is “systemd”? 1. A “System and Service Manager” for Linux • An init system (like sysv/init) • A service manager 2. A software suite for Linux • Including 1.
5. What is “systemd”? 1. A “System and Service Manager” for Linux • An init system • A service manager • Manages services as “unit” 2. A software suite for Linux • Including 1. • systemd(service manager), journald, systemd-tmpfiles, …
6. Boot up process w/ systemd • Run /usr/lib/systemd/systemd as PID=1 • Construct a dependency tree from default.target (target is a group of units) • Run dependencies concurrently
7. How to configure systemd? • systemd is configured via plain-text files • Called “unit file” • Ini-style configuration file • There’re various type of units
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9. How to use systemd units? • Use systemctl to operate systemd units • Analyze system status • Use systemd units • Manage power
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11. Where is systemd unit files? • Basically placed in two places: • /usr/lib/systemd/system/ • Units provided by installed packages • /etc/systemd/system/ (primary) • Units installed by the system admin
12. The structure of unit files • Unit files consists of three sections 1. [Unit] section • Generic information about the unit 2. [Install] section • Installation information for the unit 3. Type-specific section
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15. service
16. Systemd Service Unit • Daemon / Service definition controlled and supervised by systemd • The extension is .service • Most of the cases, WantedBy may be multi- user.target
17. [Service] Section Options 5ZQF TFSWJDF
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18. Service Startup Type • Simple(default): expected the unit started immediately after the main service process has been forked off • forking: expected the process will call fork() • oneshot: expected the unit up after the main process exits
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20. timer
21. systemd timer • Timer-based service activation like crontab • The extension is .timer • foo.timer calls foo.service by default • WantedBy=timers.target • systemctl list-timers to list up current active timers • Two type of timer
22. Monotonic Timers • Activated after a time span relatively • OnActivateSec: after activated the timer • OnBootSec: after booted up the machine • OnStartupSec: after systemd was started • OnUnitActiveSec: after last activated • OnUnitInactiveSec: after last deactivated
23. Realtime Timers • a.k.a. wallclock timers • Activate on a calendar event • The same way that cron jobs do • Use OnCalendar option
24. Realtime Timer Configs • Configure using systemd time spec • DayOfWeek Year-Month-Day Hour:Minute:Second Timezone • Some shorthand is predefined • … , monthly, weekly, yearly, quarterly… • Weekday is defined as English name • Wed or Wednesday • * is for wildcard, .. is for range, / is for repetition, ~ is for last
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26. PROS: Diff with Crontab • Jobs can be easily ran independently of timers • So easy to debug • Jobs can be set up to depend on other units • Jobs can be set up with specific environment • The logs are reported into journal
27. CONS: Diff with Crontab • Creation redundant • Need to create two files: service and timer • Need to run two times systemctl • There’s no built-in equivalent to MAILTO • But can configure like MAILTO
28. systemd-run • run the specified command in a transient • to create transient service • to create transient timer # systemd-run --on-calendar=weekly curl -X POST https://...
29. systemd journal
30. What is journald? • A log system provided by systemd • systemd-journald.service • Save logs into /var/run/log/journal • Auto-collect logs from stdout/stderr of systemd services • Syslog messages from local processes • Message posted to journald API
31. How to Read journald Logs? • Use journalctl to read journald logs • Journals are binary-formatted • There're many, useful options • Match by fields • Colored
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34. Configure journald • /etc/systemd/journald.conf • Max / Keep Disk Usage • Log Rate Limit • Forwarding to rsyslog
35. References • https://www.freedesktop.org/software/ systemd/man/systemd.unit.html
36. Q?