My thoughts on Slackware, life and everything

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 and some developer talk can be found here:

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:


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):


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.



  1. Tai

    I’m gonna try this with some older P4 dells with onboard intel video 82845g. They had horrible problems with 13.1 and current. Known issues apparently. I followed a link in one of your previous posts without any success. Thanks for your efforts Eric, it’s appreciated.

  2. BJ

    I will try this out since I have the same problem with my Intel card. One remedy for when this happens — besides the hard reboot — is running something like:
    DISPLAY=:0 kwin –replace

  3. Martinezio


    I mentioned about disabling desktop effects compatibility checks in this thread on LinuxQuestions forum:

    I think, that this checks are too much processor-and-memory-consumable, and all the owner should know their GPU capabilities, so those checks are usefull for normal users.
    They are helpfull, when some problems occurs to help detect the issue. But for daily use are not needed.

    I keep them disabled and all works smoother, than before.

    Best regards 🙂

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