KDM does not properly reset the X server. It must be set to terminate it, or the display will hang when the user logs out.

[Ryan Farmer]

I've had a problem with KDM not properly resetting the X server on log out for the last few releases of Kubuntu. The problem still exists in the 12.04 development branch.

On log out, the server does not reset itself and the display goes black or gray except for a mouse cursor.

Opening /etc/kde4/kdm/kdmrc and uncommenting the line

#TerminateServer=true

to

TerminateServer=true

fixes the problem.

The next time I log into KDE, the setting takes effect, and logging out works properly. On log out, the X server is terminated and a new instance is started and I am presented with the KDM log in screen.

I have noticed several other distributions that have apparently given up and changed the KDM setting to have the X server terminate itself instead of attempting to reset. I can only guess that others have had the same problem and that resetting the server is far from guaranteed to work.

Someone on the #kubuntu channel on Freenode suggested that it might be a video driver issue. I only use RadeonHD cards, and I only use the free/open drivers most of the time. I have checked and the behavior occurs with FGLRX as well.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: kdm 4:4.7.97-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-10.18-generic 3.2.1
Uname: Linux 3.2.0-10-generic x86_64
ApportVersion: 1.91-0ubuntu1
Architecture: amd64
Date: Wed Jan 25 02:49:25 2012
InstallationMedia: Kubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120124)
ProcEnviron:
 LANGUAGE=
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: kde-workspace
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.kde4.kdm.kdmrc: 2012-01-24T21:52:28.927927

[Jonathan Thomas (echidnaman)]

Yeah, sometimes the video drivers crap their pants and crash X on logout.

We've taken the other route and have started forcing a server restart on logout for 12.04, like the other distros. It's faster not to restart, but I guess we can't help it if it causes crashes....