No obvious way for root to cleanly shut down a session

Binary package hint: gnome-session

There does not seem to be a way for root to cleanly shut down a particular gnome-session.

Obviously restarting gdm works, but that kills all sessions. In my environment, users
share machines and we have lots of "switch user" activity. What I'm really trying
to do is to automatically clean up those sessions that are left and forgotten:
otherwise they build up and eventually every user is logged onto every machine.

Apparently, you need to send a message on the dbus to gnome-session, but getting the session ID
for a particular user/process ID isn't trivial. One would really like to be able to send
a signal to gnome-session, and have it gracefully shut down whatever it can.
(Obviously, I can do kill -9, but that can cause trouble if gnome-session needs to do clean-up
activities.)

So, _basically_, the bug is that gnome-session ignores all signals. It shouldn't. There are perfectly
good reasons for responding to signals.

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: gnome-session 2.30.0-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.32-25.44-generic 2.6.32.21+drm33.7
Uname: Linux 2.6.32-25-generic x86_64
Architecture: amd64
Date: Mon Oct 4 07:08:30 2010
InstallationMedia: Ubuntu 10.04.1 LTS "Lucid Lynx" - Release amd64 (20100816.1)
PackageArchitecture: all
ProcEnviron:
 PATH=(custom, user)
 LANG=en_GB.utf8
 SHELL=/bin/bash
SourcePackage: gnome-session