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systemd-timer.md

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Systemd Timer Instead of Cronjob

Cronjobs are quick and efficient for mostly backend automation or lightweight notifications, but are rather tedious in situations where embedded applications have permissions restrictions or behave weirdly without a full userspace or env import.

systemd user services (with timers) seem to be a nice alternative (for systemd-based Linux distros.)

  • systemd user files run as the user and don't require sudo or root to setup or run.

Necessary files

  • Timer script
  • Service script
  1. If ~/.config/systemd/user/ doesn't exist, create it:
mkdir -p ~/.config/systemd/user/
  1. Create the service file: myscript.service in ~/.config/systemd/user/:
[Unit]
Description=Conscise description of this service
ConditionPathExists=/your/path/to/script

[Service]
ExecStart=/your/path/to/script

[Install]
WantedBy=default.target
  1. Create the timer file (schedule) for myscript as myscript.timer:
[Unit]
Description=Concise description of this scheduler

[Timer]
OnBootSec=2min
OnUnitActiveSec=5m

[Install]
WantedBy=timers.target
- **OnBootSec** = how soon to start the service after boot
- **OnUnitActiveSec** = frequency threshold to re-launch `myscript`
  1. Confirm your directory looks like so:
~/.config/systemd/user/:
├── myscript.service
└── myscript.timer

  1. Activate the service (script) on every startup:

    One and done command; this won't need to be run again after the timer is active.

systemctl --user enable myscript

  1. Set the timer for startup during boot:

    One and done command; this won't need to be run again after the timer is active.

systemctl --user enable myscript.timer

  1. Set the timer for startup during boot:

    One and done command; this won't need to be run again after the timer is active.

systemctl --user enable myscript

  1. Start the service

    One and done command; this won't need to be run again after the timer is active.

systemctl --user start myscript --now

  1. Start the timer:

    One and done command; this won't need to be run again after the timer is active.

systemctl --user start myscript.timer --now

That's it!

Modifying the script after the service is active

  • Modifying the script doesn't appear to require a restart
  • Modifying the service or timer settings will require a simple restart of a daemon: 
    systemctl --user daemon-reload

Troubleshooting

systemd user services have the same tools available as system-level services.

  • See when the timer is scheduled to run next:

    systemctl --user status myscript.timer

  • Check if everything is going smoothly with the service

    systemctl --user status myscript

    (note that inactive/dead isn't what you may think; it simply means the service did it's job and went dormant. The timer will come by and activate it when it's scheduled to.)

  • Restart the timer:

    systemctl --user restart myscript.timer

  • Restart the service:

    systemctl --user restart myscript

  • Stop the timer:

systemctl --user stop myscript.timer
  • Stop the script:
systemctl --user stop myscript

The Arch Linux systemd/user wiki has much greater detail for additional options and features.