Systemd/timers/en - Revision history

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← Older revision		Revision as of 22:30, 7 October 2025
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	== Configuration ==		== Configuration ==
	The following example timer runs a systemd unit every 5 minutes which invokes a bash script.		The following example timer runs a systemd unit every 5 minutes which invokes a bash script.
	<~~syntaxHighlight~~ lang="nix">		<syntaxhighlight lang="nix">
	systemd.timers."hello-world" = {		systemd.timers."hello-world" = {
	wantedBy = [ "timers.target" ];		wantedBy = [ "timers.target" ];
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	OnBootSec = "5m";		OnBootSec = "5m";
	OnUnitActiveSec = "5m";		OnUnitActiveSec = "5m";
			# Alternatively, if you prefer to specify an exact timestamp
			# like one does in cron, you can use the `OnCalendar` option
			# to specify a calendar event expression.
			# Run every Monday at 10:00 AM in the Asia/Kolkata timezone.
			#OnCalendar = "Mon --* 10:00:00 Asia/Kolkata";
	Unit = "hello-world.service";		Unit = "hello-world.service";
	};		};
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	Type = "oneshot";		Type = "oneshot";
	User = "root";		User = "root";
			RemainAfterExit = true; # Prevents the service from automatically starting on rebuild. See https://discourse.nixos.org/t/how-to-prevent-custom-systemd-service-from-restarting-on-nixos-rebuild-switch/43431
	};		};
	};		};
	</~~syntaxHighlight~~>		</syntaxhighlight>


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	</syntaxhighlight>		</syntaxhighlight>
	in your terminal.		in your terminal.

			==== Verifying your timestamp for systemd.time ====
			If you do not understand the format that [https://www.freedesktop.org/software/systemd/man/latest/systemd.time.html systemd.time] expects, you can use the <code>systemd-analyze</code>'s <code>calendar</code> sub-command to understand the next ''N'' times when the timer will get triggered. Following is an example:<syntaxhighlight lang="shell-session">
			$ systemd-analyze calendar --iterations=5 "10:00:00"
			Original form: 10:00:00
			Normalized form: --* 10:00:00
			Next elapse: Sat 2024-12-07 10:00:00 IST
			(in UTC): Sat 2024-12-07 04:30:00 UTC
			From now: 33min left
			Iteration #2: Sun 2024-12-08 10:00:00 IST
			(in UTC): Sun 2024-12-08 04:30:00 UTC
			From now: 24h left
			Iteration #3: Mon 2024-12-09 10:00:00 IST
			(in UTC): Mon 2024-12-09 04:30:00 UTC
			From now: 2 days left
			Iteration #4: Tue 2024-12-10 10:00:00 IST
			(in UTC): Tue 2024-12-10 04:30:00 UTC
			From now: 3 days left
			Iteration #5: Wed 2024-12-11 10:00:00 IST
			(in UTC): Wed 2024-12-11 04:30:00 UTC
			From now: 4 days left
			</syntaxhighlight>

	====Using the <code>systemd.services.<name>.startAt</code> shorthand====		====Using the <code>systemd.services.<name>.startAt</code> shorthand====

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 };
 </syntaxHighlight>
 The following example 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 off.
 <syntaxHighlight lang="nix">

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{{Systemd/breadcrumb}}

Timers are systemd unit files whose name ends in .timer that control .service files or events. Timers can be used as an alternative to <code>cron</code>. Timers have built-in support for calendar-based events and monotonic time events, and can be run asynchronously.
== Configuration ==
The following example timer runs a systemd unit every 5 minutes which invokes a bash script.
<syntaxHighlight lang="nix">
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";
};
};
</syntaxHighlight>
The following example 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 off.
<syntaxHighlight lang="nix">
...
timerConfig = {
OnCalendar = "daily";
Persistent = true;
};
};
</syntaxHighlight>
More examples can be found at the [https://wiki.archlinux.org/title/Systemd/Timers Arch Wiki] and at the <code>systemd.timer</code> manpage.
== Usage ==
List active timers and their current state:
<syntaxhighlight lang="bash">
systemctl list-timers
</syntaxhighlight>
Manually run a service once for testing purposes:
<syntaxhighlight lang="bash">
systemctl start hello-world
</syntaxhighlight>
[[Category:systemd]]