Systemd/timers

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Revision as of 13:18, 11 September 2023 by imported>Papanito (add missing space)

Timers are systemd unit files whose name ends in .timer that control .service files or events. Timers can be used as an alternative to cron. Timers have built-in support for calendar time events, monotonic time events, and can be run asynchronously.

Configuration

Following example timer runs a systemd unit every 5 minutes which invokes a bash script

systemd.timers."hello-world" = {
  wantedBy = [ "timers.target" ];
    timerConfig = {
      OnBootSec = "5m";
      OnUnitActiveSec = "5m";
      Unit = "hello-world.service";
    };
};

systemd.services."hello-world" = {
  script = ''
    set -eu
    ${pkgs.coreutils}/bin/echo "Hello World"
  '';
  serviceConfig = {
    Type = "oneshot";
    User = "root";
  };
};

The following example would starts once a day (at 12:00am). When activated, it triggers the service immediately if it missed the last start time (option Persistent=true), for example due to the system being powered of

...
  serviceConfig = {
      OnCalendar = "daily";
      Persistent = true; 
  };
};

Some more examples can be found here and here.

Usage

List active timers and their current state

systemctl list-timers

Manually run service once for testing purpose

systemctl start hello-world