[systemd-devel] umounting FS happens to be at the same time as shutting down services

[Lennart Poettering]

On Sun, 22.11.15 15:26, Francis Moreau (francis.moro at gmail.com) wrote:

> Hi,
> 
> While rebooting, It seems to me that shutting down services while
> unmounting some FS at the same time in an unordered fashion is not a
> good idea since unmounting a FS can happen before a service using this
> FS is stopped.
> 
> Is this expected ?

No, and it's not really what happends. Mounts from /etc/fstab are
usually ordered with a Before= depdendency against local-fs.target,
which is ordered Before= basic.target, which is the target that normal
services are ordered After=. Hence, at startup you get the strict
order:

   Mounts from /etc/fstab → local-fs.target → basic.target → normal services

Now, in systemd the shutdown order is always the strict reverse of the
start-up order, hence this results in this shutdown order:

   normal services → basic.target → local-fs.target → Mounts from /etc/fstab

Thus, file systems are unmounted only *after* normal services have been
terminated.

Now, there are some services that set DefaultDependencies=no, and some
mount units too. For those these automatic dependencies are not in
effect, and they basically explicitly ask for the right to be ordered
manually against whatever they want to be ordered against, and thus
possibly are started or stopped in parallel. However, that's explicit
configuration that way, and the exception.

Lennart

-- 
Lennart Poettering, Red Hat