[systemd-devel] Unmountable mounts and systemd-fsck at .service conflicting with shutdown.target

[Valentin David]

It is a call to systemd-mount done from initramfs. It ends up in
/run/systemd/transient and survives the root switch. The generated unit
contains Requires=systemd-fsck at ....service.

Is the conflict on shutdown.target to make shutdown kill fsck if it is
running?

Generated systemd-cryptsetup at .service units have "DefaultDependencies=no"
and no conflict on shutdown. Maybe this is missing then. "cryptsetup
attach" might be running.


On Fri, Jan 6, 2023 at 1:34 PM Lennart Poettering <lennart at poettering.net>
wrote:

> On Do, 05.01.23 14:18, Valentin David (valentin.david at canonical.com)
> wrote:
>
> > Hello,
> >
> > In Ubuntu Core, we have some mounts that cannot be unmounted until we
> have
> > switched root.
> >
> > To simplify, this looks like that:
> >
> > / mounts a ro loop devices backed by /some/disk/some/path/image.img
> > /some/disk mounts a block device (let's say /dev/some-block0p1)
> >
> > In this case, /some/disk cannot be unmounted.
> >
> > We do not want to lazily unmount, we cannot get errors if something
> fails.
> > (Unless we had a lazy unmount that would only work when read-only)
> >
> > We do remount /some/disk read-only on shutdown. And in the shutdown
> > intramfs, we unmount /oldroot/some/disk.
> >
> > However, we get an error message with systemd trying to unmount it. While
> > functionally, it does not matter, it is still very problematic to have
> > error messages.
> >
> > Using `DefaultDependencies=no` is not enough. I have tried to be clever
> and
> > add some-disk.mount to shutdown.target.wants so it would not try to
> unmount
> > it. But systemd got confused with conflicts and randomly kills stop jobs
> > until there is no conflict.
> >
> > Debugging it, I have found that this is because some-disk.mount depends
> on
> > systemd-fsck at some\x2dblock0p1.service. And systemd-fsck at .service
> conflicts
> > with shutdown.target.
> >
> > I wonder if having conflict on shutdown.target really needed. Could we
> > remove it? (And also add DefaultDepenencies=no to
> > system-systemd\x2dfsck.slice) With this, mounts with
> DefaultDependencie=no
> > do not get unmounted as part of shutdown.target. (They do during
> > systemd-shutdown)
>
> hmm, so we generally want system services to go away before
> shutdown. This is a very special case though. I wonder if we can just
> override systemd-fsck@….service for that specific case?
>
> How are those mounts established? i.e. by which unit is the
> systemd-fsck at .service instance pulled in? and how was that configured?
> fstab? ubuntu-own code?
>
> Lennart
>
> --
> Lennart Poettering, Berlin
>
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