Black Screen on Logout

Symptom:

You log out from your desktop environment and the screen goes black. Ctrl-alt-F1 does not make a text console visible -- or if done from within the session, it may induce the black screen itself. But the machine is still on the net, and ctrl-alt-del triggers a normal shutdown, i.e. the keyboard is not frozen.

What's going on:

I did a search on Google for 'xfce4 ATI OR fglrx OR FireGL "black screen"', getting 10800 hits. The symptoms described are rather varied. In my specific situation the desktop environment is Xfce4 (Gnome also gave trouble for other people); the graphics card is an ATI Radeon Mobility X1400 with the fglrx (FireGL) driver (other people report similar symptoms with various nVidia or Intel 950 or SiS onboard video); and I am not using the Composite extension (others say that using it is beneficial for this symptom).

It's not clear what's going on, but it's clearly related to the black screen that bedevils many people when suspending their machines to RAM or disc. In my case, when I upgraded Xfce4 from version 4.2 to 4.4, the machine started doing the black screen thing and also could no longer suspend, i.e. it stopped tasks and tried to shut down drivers, but failed and emerged from suspend mode. The video driver is definitely at fault, but something in the window manager (etc.) makes it choke. A number of users speculate that 3D acceleration (DRI) is the culprit, since users who introduce the Beryl and Compiz window managers often report this failure.

How to fix:

• Update your X-Windows driver. For fglrx, I had version 8.36.5 and it failed; one person upgraded to 8.37.6 and got a cure; I upgraded to the currently latest version, 8.40.4 dated 2007-08-13, and my problem was solved.

• If upgrading is impossible or ineffective, try making the display manager kill and restart the X-server upon logout. Edit gdm.conf (/etc/opt/gnome/gdm/gdm.conf on my SuSE 10.2 system) and in the [daemon] section set AlwaysRestartServer=true. There are analogous settings for kdm and xdm. Many people report that this maneuver cures their problem.

• If problems remain, such as failure to suspend to RAM, you could try to identify what program (e.g. window manager) is doing 3D rendering, and get rid of it or make it stop.