Re: [gentoo-amd64] Systemd migration: opinion and questions

[Marc Joliet]

Am Sun, 1 Mar 2015 19:20:02 +0100
schrieb Marc Joliet <marcec@×××.de>:

[...]
> But actually, while putting off finishing this email, I came to the realisation
> that I could of course use WantedBy= in [Install], and following that idea I
> ended up with the following [Unit] and [Install] sections:
>
>     [Unit]
>     Description=Run hourly backups (timer)
>     Requisite=media-MARCEC_BACKUP.mount
>     BindsTo=media-MARCEC_BACKUP.mount
>     After=media-MARCEC_BACKUP.mount
>
>     [Install]
>     WantedBy=timers.target
>     WantedBy=media-MARCEC_BACKUP.mount
>
> So the mount point and the timer both depend on each other (with the mount unit
> starting first), so the mount tries to start the timer and vice versa, but only
> the timer fails if the mount point doesn't exist.  And the BindsTo sees to it
> that the timer disappears if the mount does.  Preliminary tests show that it
> works: unmounting with udiskie shows that the backup timer disappears, and it
> re-appears after mounting the file system again.
>
> I'll have to see what the behaviour is during a cold boot.  The Requisite
> dependency on the mount point *should* make the Restart line in the
> corresponding service obsolete, since the WantedBy should make the timer start
> once the mount point shows up.  I could probably alternatively use
> ConditionPathIsMountPoint instead, but I think I prefer the timer failing.
[...]

Just FYI: I undid that fairly quickly since BindsTo is a superset of Requires,
thus systemd waits for 1m30s for the mount point to show up.  Ouch.

-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup