Comment 20 for bug 119635

Etienne,

What is common to all these bug reports is that neither Xorg.0.log nor dmesg show anything unusual. To see what your problem is, you need to try to produce a core dump, look at it with gdb, and post the backtrace to this forum.

Now I don't run (K)ubuntu, so I do not now the specifics of your platform. However, I would guess you should
(i) Login to a console
(ii) sudo su - # become root
(iii) ulimit -c unlimited # allow core dumps
(iii) startx -- :1 # start X on a new display. (If :1 is taken, use :2 etc.)
You should now see a new X display, with one (or more) open xterm(s) on it. Continue in the top-left xterm:
(iv) exit # this is the same as logging out of X and should reproduce your crash.

If all went well, the core dump is now in the directory where you typed startx. Reboot your system, go to this directory, and type "gdb /usr/bin/X core". At the gdb prompt, just type 'bt' and return.

In order to produce a readable backtrace, I suspect that you will also need to have debug libraries (or debugging symbols) installed for glibc, mesa and X.

Bram