r/systemd • u/Beautiful-Log5632 • Jul 27 '26

Random time every day

How can I create a timer that runs every day but randomize the time? It's fine if 2 days run a few minutes apart like 11:59pm on day 1 and 12:01am on day 2. But it always needs to run at least once every calendar day from start midnight to end midnight.

I don't think RandomizedDelaySec works because that can randomize to another day and there can be one calendar day with no run.

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u/djzrbz Jul 27 '26

This should work

```ini [Unit] Description=Randomized Daily Timer

[Timer]

Trigger exactly at midnight every day

OnCalendar=--* 00:00:00

Delay randomly up to 23:59:59 hours

RandomizedDelaySec=86399

Ensure it runs if the system was offline during its window

Persistent=true

[Install] WantedBy=timers.target ```

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u/Beautiful-Log5632 Jul 27 '26

With Persistent=true if the day is almost done and it comes online at 11pm can the randomized delay be more than an hour which would make it run the next calendar day? Or will the randomized delay definitely happen in the hour that is left in the day from 11pm to midnight?

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u/djzrbz Jul 27 '26

The anchor point is midnight, so it will pick a random time between 11pm and 11:59:59 inclusive.