今更聞けないsystemd - Now Beginning Systemd

builderscon tokyo 2019

Transcript

1. Now Beginning
   Systemd
   @nasa9084
   

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2. $ whoami
   • @nasa9084
   • LINE Corp.
   • Go / Kubernetes Engineer
   

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3. systemd
   

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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.
   

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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, …
   

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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
   

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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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   Major unit types
   

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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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10. Systemctl commands
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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
    

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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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13. [Unit] Section
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14. [Install] Section
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15. service
    

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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
    

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17. [Service] Section Options
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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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19. Restart
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20. timer
    

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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
    

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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
    

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23. Realtime Timers
    • a.k.a. wallclock timers
    • Activate on a calendar event
    • The same way that cron jobs do
    • Use OnCalendar option
    

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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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    Calendar Event Examples
    

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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
    

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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
    

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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://...
    

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29. systemd journal
    

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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
    

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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
    

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35. References
    • https://www.freedesktop.org/software/
    systemd/man/systemd.unit.html
    

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36. Q?
    

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