No X acceleration (DRI) in Jaunty: solved (Shallow Thoughts)

Akkana's Musings on Open Source Computing, Science, and Nature.

Sun, 07 Jun 2009

No X acceleration (DRI) in Jaunty: solved

I upgraded to Ubuntu's current 9.04 release, "Jaunty Jackalope", quite a while ago, but I haven't been able to use it because its X server crashes or hangs regularly. (Fortunately I only upgraded a copy of my working 8.10 "Intrepid" install, on a separate partition.)

The really puzzling thing, though, wasn't the crashes, but the fact that X acceleration didn't work at all. Programs like tuxracer (etracer) and Google earth would display at something like one frame update every two seconds, and glxinfo | grep renderer said

OpenGL renderer string: Software Rasterizer

But that was all on my old desktop machine, with an ATI Radeon 9000 card that I know no one cares about much. I have a new machine now! An Intel dual Atom D945GCLF2D board with 945 graphics. Finally, a graphics chip that's supported! Now everything would work!

Well, not quite -- there were major teething pains, including returning the first nonworking motherboard, but that's a separate article. Eventually I got it running nicely with Intrepid. DRI worked! Tuxracer worked! Even Google Earth worked! Unbelievable!

I copied the Jaunty install from my old machine to a partition on the new machine. Booted into it and -- no DRI. Just like on the Radeon.

Now, there's a huge pile of bugs in Ubuntu's bug system on problems with video on Jaunty, all grouped by graphics card manufacturer even though everybody seems to be seeing pretty much the same problems on every chipset. But hardly any of the bugs talk about not getting any DRI at all -- they're all about whether EXA acceleration works better or worse than XAA and whether it's worth trying UXA. I tried them all: EXA and UXA both gave me no DRI, while XAA crashed/rebooted the machine every time. Clearly, there was something about my install that was disabling DRI, regardless of graphics card. But I poked and prodded and couldn't figure out what it was.

The breakthrough came when, purely by accident, I ran that same glxinfo | grep renderer from a root shell. Guess what?

OpenGL renderer string: Mesa DRI Intel(R) 945G GEM 20090326 2009Q1 RC2 x86/MMX/SSE2

As me (non-root), it still said "Software Rasterizer." It was a simple permissions problem! But wait ... doesn't X run as root?

Well, it does, but the DRI part doesn't, as it turns out. (This is actually a good thing, sort of, in the long term: eventually the hope is to get X not to need root permissions either.)

Armed with the keyword "permissions" I went back to the web, and the Troubleshooting Intel Performance page on the Ubuntu wiki, and found the solution right away. (I'd looked at that page before but never got past the part right at the beginning that says it's for problems involving EXA vs. UXA vs. XAA, which mine clearly wasn't).

The Solution

In Jaunty, the user has to be in group video to use DRI in X. But if you've upgraded from an Ubuntu version prior to Jaunty, where this wasn't required, you're probably not in that group. The upgrader (I used do-release-upgrade) doesn't check for this or warn you that you have desktop users who aren't in the video group, so you're on your own to find out about the problem. Fixing it is easy, though: edit /etc/group as root and add your user(s) to the group.

You might think this would have been an error worth reporting, say, at X startup, or in glxinfo, or even in /var/log/Xorg.0.log. You'd think wrong. Xorg.0.log blithely claims that DRI is enabled and everything is fine, and there's no indication of an error anywhere else.

I hope this article makes it easier for other people with this problem to find the solution.

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[ 19:23 Jun 07, 2009    More linux/install | permalink to this entry | comments ]
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