Bug#934491: libelogind0: failing to switch from systemd to sysvinit-core/elogind results in libsystemd.so.0 disappearing

[Mark Hindley]

On Thu, Aug 15, 2019 at 08:02:51PM +0100, Simon McVittie wrote:
> On Thu, 15 Aug 2019 at 18:33:20 +0200, Thorsten Glaser wrote:
> > On Thu, 15 Aug 2019, Mark Hindley wrote:
> > > At this point apt has failed to remove systemd/241-7 which depends on libsystemd
> > > (=241-7). Surely it should not then go on to try and remove the systemd
> > > dependency?
> > 
> > Unsure if that’s apt or dpkg. Plus, the failing prerm is in systemd,
> > not in libsystemd0.
> 
> I think this is probably dpkg, but it's dpkg being told what to do by
> apt, so it could be either one causing this. I would have hoped that if
> systemd.prerm fails, that's a fairly heavy hint that not only is it not
> OK to remove systemd at this time, it's also not OK to remove systemd's
> dependencies.

Yes, but that appears not to happen.

> I still wonder whether apt/dpkg are being forced into this by libelogind0
> using Conflicts rather than Breaks - Conflicts is a stronger relationship
> than Breaks, and forces libsystemd0 to be removed altogether, not just
> deconfigured (marked as "broken"), before unpacking libelogind0. That
> means there's an unavoidable window during which libsystemd0 no longer
> provides libsystemd.so.0, but libelogind0 doesn't provide it yet.

I don't think so because the versions are different. systemd 241-7 Depends on
libsystemd0 =241-7 (= ${binary:Version}). libelogind0 Provides libsystemd0
=241.3 (= ${source:Upstream-Version}. That can never satisfy the systemd
dependency.

I am pretty sure I tried with Breaks and the result was the same.

Mark