How to synchronize systemd stop order from one service?
How to synchronize systemd stop order from one service?
Suppose I have a.service which I cannot modify, and b.service which I can modify, I want to see this stop order:
a.service
b.service
Stopping b.service ...
Stopped b.service
Stopping a.service ...
Stopped a.service
instead of this:
Stopping b.service ...
Stopping a.service ...
Stopped b.service
Stopped a.service
Assume that b.service may take at least 20 seconds to finish.
b.service
2 Answers
2
In order to stop b.service before a.service, you need to actually order b.service after a.service, since the ordering at service stop time is the inverse of the order at start time.
b.service
a.service
b.service
a.service
So this should be enough to accomplish what you described:
See the documentation for After= in man systemd.unit, which states:
After=
man systemd.unit
Note that when two units with an ordering dependency between them are shut down, the inverse of the start-up order is applied. i.e. if a unit is configured with After= on another unit, the former is stopped before the latter if both are shut down.
After=
You also asked about what happens if b.service takes at least 20 seconds to terminate. That is fine. If b.service is properly configured so systemd is able to monitor it until unit stop is completed (in other words, if ExecStop= is not somehow misconfigured) and if it stops before the timeout is reached (see TimeoutStopSec=), then systemd will wait until b.service is fully stopped before initializing shutdown of a.service.
b.service
b.service
ExecStop=
TimeoutStopSec=
b.service
a.service
Oh I think I got confused because I saw
Stopped Qubes DB agent.(as a.service) right after Stopped Qubes Dom0 startup setup(as b.service) and I assumed there should've been a Stopping Qubes DB agent... inbetween, but there wasn't because Qubes DB agent service is lacking any ExecStop= lines! So I thought the Stopping of a.service happened earlier than the Stopped for b.service which I took to mean that it didn't wait for b.service to fully stop before trying to stop a.service. But I was wrong. Thank you for your great answer!– Marcus Linsner
Sep 3 at 21:54
Stopped Qubes DB agent.
a.service
Stopped Qubes Dom0 startup setup
b.service
Stopping Qubes DB agent...
Qubes DB agent
ExecStop=
Stopping
a.service
Stopped
b.service
b.service
a.service
Looks like it sometimes doesn't work, or there's something else happening. I tried 3 consecutive boots since I added
dev-block-253:0.device to my After= in qubes-core.service (and did a sudo systemctl daemon-reload of course) and the 3rd boot acted as if I hadn't added that so the order wasn't respected! all details here: gist.github.com/constantoverride/… (where qubes-core.service is just a page scroll above). I must be missing something, or is it a systemd bug?– Marcus Linsner
Sep 4 at 1:52
dev-block-253:0.device
After=
qubes-core.service
sudo systemctl daemon-reload
qubes-core.service
If you merely want to stop these in a given order you can invoke the call to systemctl like this:
systemctl
$ systemctl stop a.service && systemctl stop b.service
or
$ systemctl stop a.service; systemctl stop b.service
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Related - serverfault.com/questions/785127/….
– slm♦
Sep 3 at 21:52