[systemd-devel] How to prevent sleep during running oneshot units

[Mirco Tischler]

Am 13.02.2014 00:14 schrieb "Kai Krakow" <hurikhan77 at gmail.com>:
>
> Mirco Tischler <mircotischler at gmx.net> schrieb:
>
> > It's late here so excuse me if I'm missing something. But wouldn't a
> > simple Before=sleep.target suffice to implement b)?
>
> I'm not sure... The unit is not enabled, only triggered by the timer - so
it
> may work. I think I may try that as an alternative to systemd-inhibit.
> Systemd-inhibit just does not feel like the right tool for this.
>
> > If your backup job is still running it blocks sleep.target's start until
> > it finishes.
>
> Then, what happens if I start using my system during backup, sleep.target
> had been triggered but is waiting for the backup job to finish? Will it
> simply go to sleep then while I am using the system? OTOH, will systemd-
> inhibit cover that case?
>
Yeah, the job to start sleep.target will still be active, so this should
only work for overnight stuff.
> Twisted around: What happens if sleep is triggered by the system due to
idle
> time while sleep is inhibited? Will it trigger as soon as the inhibit is
> removed again? Or will the idle timer for my system just trigger sleep
again
> after it has passed a second time?
>
Systemd-inhibit has the options block and delay for this. But when and if
the idle time gets restarted is up to the idle timer ;-)
> > Though for the grace period some ugly hack such as
> > "ExecStartPost=/usr/bin/sleep <n>" would be required.
>
> My primary concern here is btrfs doing a lot of background work when
> handling snapshots. My backup medium is a btrfs with rsync copying the
> source as in-place deltas to a scratch area, then taking a snapshot of it.
> Later, I'd like to automatically cleanup old snapshots - but that means I
> should wait before going back to sleep until btrfs finished that job. A
> simple "sleep" probably won't do. I suppose it would require an option
like
> "--wait" to "btrfs subvolume delete", then wait another 5 minutes to give
> all pending write commits a chance to make it to disk.
Sounds like you want systemd-inhibit for both your backup service and the
btrfs subvolume delete 'service'. And the kernel will call sync() before
suspending, shouldn't that suffice?
>
> --
> Replies to list only preferred.
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