Daily Archives: October 16, 2010

Compositing hard lock in KDE 4.5

People have written about their computer locking up with KDE 4.5.x in Slackware.

These locks seem to be caused by the open source video drivers that are part of X.Org. These drivers incorrectly advertise some OpenGL capabilities when the KDE compositing manager queries them. As a result, the KDE window manager tries to enable non-working functionality in “3d desktop effects” which results in a hard lock of X.Org.

There was some talk about this when I first released KDE 4.5.1 packages, see the comments section of http://alien.slackbook.org/blog/kde-4-5-1-i-took-the-plunge/ and some developer talk can be found here: http://blog.martin-graesslin.com/blog/2010/09/driver-dilemma-in-kde-workspaces-4-5/

Today I installed Slackware-current on an “old” ThinkPad T41 with an onboard Radeon RV250 (Mobility FireGL 9000) graphics chip. I experienced the hard lock there for the first time.

This is what I did to get KDE running (after forcedly shutting down the machine by pressing the OFF button for 8 seconds…): edit the KDE Window Manager configuration file:

~/.kde/share/config/kwinrc

In that file, look up the section called “[Compositing]” and then add these lines (perhaps in your case you have to modify, not add lines):

DisableChecks=true
Enabled=false

That first line disables the functionality checks so that if you enable “3d effects” manually you have a good chance of it actually going to work because KDE is not going to query your graphics drivers and just assumes it’ll work. As a result you will see an error about not being able to use the “blur effect” which is exactly where the query would result in incorrect data – the error message is not fatal though.

The second line disables the “3d effects” entirely, allowing KDE to start properly.

Eric