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Charles avatar Ubuntu

Systemd timer with WakeSystem=true waiting for twice the specified time

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Charles

I wanted to understand systemd timers, so I've been fiddling. I've found an odd behavior which is not what I wanted. When I start a systemd timer using WakeSystem=true and OnActiveSec setting the timer, then I suspend, the timer waits for that duration twice instead of once.

Here's an example you can try yourself:

date >> /home/user/Desktop/MyWakeLog.txt;sudo systemd-run --unit='WakeTimer' --on-active='5m'  --timer-property='AccuracySec=1s' --timer-property='WakeSystem=true' /bin/sh -c "date >> /home/user/Desktop/MyWakeLog.txt";sudo systemctl suspend

You'd expect the file MyWakeLog.txt to be written to once, then the timer starts, then it suspends. Then 5 min elapse, the computer wakes up, and the MyWakeLog.txt file is written to again.

But that's not what's happening! The timer wakes the computer up for suspend after 5 minutes, then waits another 5 minutes to write to the log!

Why is this happening? How can I get my computer to wake up after a specified time then immediately write to the log?

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