Bug#832351: init-system-helpers: purging gdm3/lightdm/sddm/xdm leaves dangling /etc/systemd/system/display-manager.service symlink

[Felipe Sateler]

Control: clone -1 -2
Control: reassign -1 xdm 1:1.1.11-3
Control: reassign -2 sddm 0.13.0-1

On Sun, 24 Jul 2016 15:54:55 +0200 Michael Biebl <biebl at debian.org> wrote:
> Am 24.07.2016 um 15:49 schrieb Andreas Beckmann:
> > Package: init-system-helpers
> > Version: 1.22
> > Severity: important
> > User: debian-qa at lists.debian.org
> > Usertags: piuparts
> > Control: affects -1 + gdm3 lightdm sddm xdm
> > Control: found -1 sddm/0.13.0-1
> > Control: found -1 xdm/1:1.1.11-3
> >
> > Hi,
> >
> > during tests with piuparts I noticed the same behavior in 4 packages
> > providing a display-manager service: a dangling symlink is left after
> > purge. Some have individual bugs filed (lightdm: #775385, gdm3:
> > #771085), but this is more likely a bug somewhere in the helpers being
> > used. Notice, that after purge no other package providing a
> > display-manager service was installed any more.
> >
>
> Those links are not created by init-system-helpers, so it's probably the
> wrong package to assign this bug too.
> The display-manager.service symlink has some custom code in the
> maintainer scripts of the individual packages.
>
> We can use this bug report though, to come up with a scheme, how to do
> that properly.
> Then again, we already have
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=764607 which is sort
> of related.

And indeed Didier Roche proposed a solution (in the form of a patch to
gdm3)[1]. I'm cloning and reassigning this bug to the two display
managers that do not have a bug already. The TLDR of the solution is:

1. Have your systemd unit Alias=display-manager.service
2. Use the --no-enable flag to dh_systemd_enable
3. Use `systemctl enable $DEFAULT_SERVICE` in the postinst

Step 1 and 2 should ensure the symlinks are removed on purge.

[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?att=1;bug=764607;filename=use-systemd-alias.debdiff;msg=19