Odd issue in linux/x11. I used to have the evil proprietary Nvidia drivers loaded. I gave up on them recently, but once I installed a new kernel without them, glx (openGL for x) stopped working. I got the error:
Xlib: extension "GLX" missing on display ":0.0"
It should have worked, as the file
/usr/X11R6/lib/modules/extensions/libglx.a should have provided this funtionality.
But alas, Xorg X11 was using the file
/usr/X11R6/lib/modules/extensions/libglx.so.1.0.5336, left over from the proprietary driver. I deleted this file, restarted X11, and it all workes correctly! I have a fast enough processor that most small openGL apps work fine without hardware acceleration.