Le 24/11/2014 10:01, Sjoerd Simons a écrit :
On Mon, 2014-11-24 at 09:31 +0100, Didier Roche wrote:
Le 21/11/2014 22:46, Sjoerd Simons a écrit :
reassign 770404 lxdm
thanks
On Fri, Nov 21, 2014 at 08:01:50PM +0000, Simon McVittie wrote:
This looks wrong. I think it might be caused by this in lxdm.service:
[Install]
Alias=display-manager.service
Neither gdm3 nor lightdm have that, which suggests that it isn't
meant to be necessary.
I think what's happening is that when you install lxdm, that Alias directive
causes the debhelper snippets in its postinst[1] to break the mechanism
that is meant to arbitrate who owns display-manager.service: the part of
its postinst headed "# set default-display-manager systemd service link"
is correct, but then the #DEBHELPER# snippet runs "systemctl enable lxdm"
which sees the Alias, obeys it, and overwrites the display-manager.service
symlink with an incorrect target.
Correct, that Alias= breaks our current mechanism for arbitrating the DM to use
(that is, the sylink and the config file go out of sync).
See also Martin pitt's comment for lightdm way back when:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=733220#25
Actually, we revisited that with Martin and we can use Alias in relation
to the correct postinst scripts to achieve this in a clean way.
See the snippet I proposed on bug #764607.
Adding Bigon and Joss to the CC for their GDM perspective ;)
Interesting. Your postinst (patch from the bug you mentioned) seems a
bit brute-force though (it tries to (re)enable the default display
manager regardless of whether it, itself, is the default). But at least
that means things stay in sync :p
However I guess that still breaks things if the user enables a
non-default DM by hand ? (iotw the DM gets enabled but will bail
resulting in no DM being started if the user doesn't also update the etc
file)
Indeed, but even manually crafted solutions will have that issue as well
(manual symlinks) as the alias is just the systemd way to do that
automatically on systemctl enable <unit>.
We are currently discussing with Laurent to maybe ensure that all dms
(the 7 in debians) have some service file as a RC bug to avoid such
things to happen. However, there is an issue with gdm3 due to it being a
symlink (will raise a bug once we found a proper way to avoid this)
Cheers,
Didier
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