Bug#801749: gdm3: Does not start anymore

[phep]

Hi,

Same problem here (on a desktop box, no VM or container) after upgrading my 
testing box. I got the "Oh no..." screen every time.

Installing xserver-xorg-legacy did not help, even when I allowed "anybody" 
and forced "yes" for "needs_root_rights".

Downgrading gdm3 to 3.14.2 finally made the trick. I can even use the Xfce 
systray applet to switch users without closing sessions. This survives reboots.

I noticed the following lines in my syslog file when gdm3 failed to start :

Nov  8 22:11:23 tarch gnome-session[2066]: Unable to init server: Impossible 
de se connecter : Connexion refusée
Nov  8 22:11:23 tarch gnome-session[2066]: ** (gnome-session-failed:2318): 
WARNING **: Impossible d'ouvrir l'affichage :

The last line roughly translates as "Cannot open display".

I kinda expected those problems when I read the News notice before to 
upgrade, but:
- the News file says one should have logind and libpam-systemd but only the 
latter is installed on my box while the former does not seems to be 
available (aptitude search logind returns nothing); yet I have files related 
to systemd-logind so I suppose this is what's needed,
- the News file says X now needs a kernel video driver but does not explain 
how one can check if we got one - here my Xorg log file says X uses the 
intel i965 driver but I don't know if it's a "kernel video driver"?
- the News file says X needs to run on the VT it was started from : will 
such a feature allow running multiple user session concurrently (I mean 
using a "switch user" feature?)

By the way, on the debian french users list someone worked around this 
problem by adding the user Debian-gdm to the video group (see bug 799948 for 
something similar) but this did not change anything on my box, I really had 
to downgrade gdm3, which is quite annoying...

Tia for any solution that would permit upgrading to the standard version of 
gdm3.

phep