I have a test machine in my basement with ubuntu on it and I upgraded it to 8.10. I was able to reproduce this problem.
Originally Posted by MisterB
It is the X server itself that is crashing. From /var/log/Xorg.0 (actually Xorg.0.old):
Please verify that all of you get the same X server crash.
0: /usr/X11R6/bin/X(xf86SigHandler+0x79) [0x80c3009]
2: /usr/X11R6/bin/X [0x8158279]
3: /usr/X11R6/bin/X(CallCallbacks+0x4e) [0x80909ae]
4: /usr/X11R6/bin/X(XaceHook+0x7e) [0x815702e]
5: /usr/X11R6/bin/X(ProcXFixesGetCursorImageAndName+0x8b) [0x8147e9b]
6: /usr/X11R6/bin/X [0x814639c]
7: /usr/X11R6/bin/X(Dispatch+0x34f) [0x808c89f]
8: /usr/X11R6/bin/X(main+0x47d) [0x8071d1d]
9: /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe5) [0xb7b93685]
10: /usr/X11R6/bin/X [0x8071101]
Saw signal 11. Server aborting.
It is pretty serious that a simple X application like x11vnc can make the X server (running as root) have a segmentation violation and crash. Potentially a security issue as well.
Note by the 'ProcXFixesGetCursorImageAndName' above, x11vnc was trying to retrieve the mouse cursor shape and image at the time.
So a workaround is to apply the '-noxfixes' option to the x11vnc command line.
Please verify that -noxfixes avoids the crash for all of you.
If you don't like the few fixed mouse cursors under -noxfixes, you will have to log in twice via the VNC viewer, e.g.:
1) Put KillInitClients=true (not false) in gdm.conf-custom
2) Put the x11vnc start line in BOTH /etc/gdm/Init/Default and /etc/gdm/PreSession/Default
3) Restart everything
This way when you connect via VNC and login at the GDM greeter x11vnc will be disconnected after you log in. Then the x11vnc in PreSession/Default will be running and you connect to it with your VNC viewer a 2nd time. Then you will have all the xfixes mouse cursors.