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89 lines
2.4 KiB
Org Mode
89 lines
2.4 KiB
Org Mode
:PROPERTIES:
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:ID: f1b21fc8-86a5-47cd-b3d8-da6ac7a34427
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:END:
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#+title: systemd timers
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#+date: 2021-07-19 21:45:47 +08:00
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#+date_modified: 2021-08-07 19:29:15 +08:00
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#+language: en
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You can schedule tasks with timers.
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If systemd is compiled with the feature, it makes cron unnecessary.
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systemd has different ways to denote time.
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- Timespans denote the duration — e.g., =100 seconds=, =5M 3w=.
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- Timestamps refer to a specific point in time — e.g., =2021-04-02=, =today=, =now=.
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- Calendar events can refer to more than one point of time — e.g., =*-*-4/2=, =Sun,Wed,Fri *-1/2-1/8=.
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To find more details about time notation, you can view the =systemd.time.5= manual page.
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Here's an example of setting a timer for an example backup service.
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The following timer unit sets it to execute every day at 18:00.
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#+begin_src ini
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[Unit]
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Description=A deduplicated backup from my computer
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Documentation=man:borg(1) https://borgbackup.readthedocs.io/
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[Timer]
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Unit=borg-backup.service
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OnCalendar=*-*-* 18:00:00
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Persistent=true
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[Install]
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WantedBy=graphical.target
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#+end_src
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If the timer unit is started, this will trigger =borg-backup.service= from the load path.
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But you can omit it if you named the timer unit file similarly (e.g., =borg-backup.timer= with =borg-backup.service=).
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You can find more information about it from the =systemd.timer.5= manual page.
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Furthermore, systemd has a testing tool for time with ~systemd-analyze {timespan,timestamp,calendar}~.
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#+begin_src shell :eval yes
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printf "Timespan example:\n"
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printf "..............\n"
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systemd-analyze timespan 4000min
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printf "..............\n\n"
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printf "Timestamp example:\n"
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printf "..............\n"
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systemd-analyze timestamp 2021-07-01
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printf "..............\n\n"
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printf "Calendar example:\n"
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printf "..............\n"
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systemd-analyze calendar "*-1/4-5 0/2:00:00"
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printf "..............\n\n"
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#+end_src
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#+results:
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#+begin_example
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Timespan example:
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..............
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Original: 4000min
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μs: 240000000000
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Human: 2d 18h 40min
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..............
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Timestamp example:
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..............
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Original form: 2021-07-01
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Normalized form: Thu 2021-07-01 00:00:00 PST
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(in UTC): Wed 2021-06-30 16:00:00 UTC
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UNIX seconds: @1625068800
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From now: 11h ago
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..............
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Calendar example:
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..............
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Original form: *-1/4-5 0/2:00:00
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Normalized form: *-01/4-05 00/2:00:00
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Next elapse: Sun 2021-09-05 00:00:00 PST
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(in UTC): Sat 2021-09-04 16:00:00 UTC
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From now: 2 months 4 days left
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..............
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#+end_example
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