[systemd-devel] mount units and symlinks

[Colin Walters]

On Mon, Jun 30, 2014, at 12:29 PM, Lennart Poettering wrote:
> 
> Why would you create such a symlink? This sounds wrong. /tmp should
> generally be a tmpfs these days, why would you link that?

I need to support cases where /tmp is not tmpfs (e.g. current Fedora
cloud images).

The rationale is the way OSTree implements atomic upgrades and parallel
OS installation involves having separate os roots, so by having /tmp ->
/sysroot/tmp they're shared rather than separate per root.

> I am pretty sure we should simply prohibit mounts on existing
> symlinks.

That would be one way to do it.  I could figure something out on the
ostree side to adapt, probably having custom units around /tmp.

There's likely other people in the field though with mount points that
are symlinks, and while they're clearly buggy it'd be rather unfriendly
to just have them entirely break after upgrading systemd.  Maybe a loud
warning?