Using 3rd Party Video Drivers
There have been a number of bugs reported in Red Hat bugzilla against X which have recently been tracked down to 3rd party video drivers being the culprit behind the problem the user was experienced. In many of the cases however, it wasn't obvious that the 3rd party drivers were at fault because the user was actually using the Red Hat supplied drivers, and not using the 3rd party driver that they had previously installed.
Developers have spent hours diagnosing issues of this nature which have later turned out to be caused by proprietary drivers having been "installed" on the system, whether they were actually being used or not, you should be informed of some pitfalls you may encounter if you even install 3rd party video drivers.
Both ATI and Nvidia, and perhaps even other 3rd party drivers out there come in some form of tarball or equivalent form from the particular vendor. Most users seem to favour the hardware vendor supplied drivers directly, rather than using more sanely packaged 3rd party packages that contain the same drivers. This is very unfortunate, because installing these 3rd party tarball driver installations is very harmful to your clean OS installation.
Both ATI and Nvidia's proprietary video driver installation utilities replace the Red Hat supplied libGL library with their own libGL. Nvidia's driver installs a replacement libglx.a X server module, removing the Red Hat supplied X.Org module in the process. ATI's driver may or may not replace libglx.a with it's own, I haven't checked (but if someone could confirm that, I'd appreciate knowing for certain).
Once you have either of these drivers installed on your system, you can no longer use DRI with any video card. So if you install the ATI fglrx driver, while you should still be able in theory at least to use the Red Hat supplied radeon driver, you may no longer be able to use DRI with the radeon driver, because ATI's driver has blown away critical files that come with the OS that are needed for proper operation.
If you install Nvidia's driver, and later decide to install an ATI card, and still have Nvidia's driver installed, bang - you will not be able to get Red Hat supplied DRI 3D acceleration to work. You must remove Nvidia's driver completely from your hard disk, and completely reinstall all of the xorg-x11 and mesa packages, and ensure they are all intact by using:
rpm -Va
Another problem being reported by a few people, is they are unable to get DRI to work because mesa libGL is looking for the DRI drivers in the wrong directory. The claim is that mesa is looking for the DRI drivers in /usr/X11R6/lib/modules.
On a fresh OS install however, my findings are that mesa's libGL very much is not looking in /usr/X11R6 for it's modules. It is looking in the proper location of /usr/lib/dri for the modules. Why then is it looking in the wrong place on some systems?
Answer: Because of fglrx having been installed. If you have had a previous OS release installed, and have installed ATI's fglrx driver from tarball, it has removed the OS supplied libGL et al and made backup copies of them aparently. Now you do an OS upgrade which works properly and installs everything in the right place. Then you uninstall ATI's fglrx with whatever script or whatever they supply, and now you try to run X, and get no DRI!
Well, since you don't have fglrx installed at all, it must be our OS at fault right! Wrong. the uninstall script has put the OLD libGL it backed up (from FC4 or whatever) back in the system, overwriting the new FC5 supplied libGL in the process, and since ATI's fglrx driver is DRI based as well, it looks for the DRI modules in the wrong place now.
To read more information on this topic you can read Mike A. Harris' full email on http://www.redhat.com/archives/fedora-devel-list/2006-February/msg01178.html