Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm having intermittent problems where the screen will freeze in Ubuntu. I've tried using Ctrl + Alt + Backspace to restart the X-server, though this does nothing. When the freeze occurs, there's a small square of black dashes around the mouse pointer - maybe 1 inch in size. These dashes look a lot like a 2d barcode. The rest of the screen looks normal, but I can't move the mouse and none of the keyboard shortcuts work to do anything. However, music that I begin playing before the freeze continues to play, which seems to indicate it hasn't stalled up completely.

I've noticed a similar freezing problem when I'm using Windows 7. That is, I see the same barcode like dashes around the mouse pointer when it freezes up. So I'm guessing it's either a driver or hardware problem. I thought if it was a hardware problem though, the whole computer might stop working (i.e. music would stop playing)? The video card I am using is an Nvidia, and I believe it's in the 7600 range. In Ubuntu I have the drivers for the card set to the latest available (proprietary). Ideally I'd like to be able to continue using the proprietary drivers. Is there any known issues with the drivers for this model graphics card, or has anyone experienced the same problem and knows how to fix it?

share|improve this question
up vote 3 down vote accepted

It's your VGA I'm pretty sure. Ctrl+alt+backspace is disabled on the newer Xorg servers (oh revolution hell yeah), but you can enable it. I used to edit the xorg.conf for this but it seems Ubuntu provides an easy way. Try this one:

About the fix: Replace your vga. About 10-15$ you can get a used 9300/7600/8400 NVidia, all of them supported by the latest drivers if I remember clearly. (Try using your PC with a different VGA and see if the problem keep occuring. Anyway, you won't be able to restart your Xorg like this since the whole PC freezes up. (No the magic combination is the same.))

share|improve this answer
It's beginning to look like I might have to try this. – Bryce Thomas May 26 '10 at 16:36
You won't be able to use this I guess. You should get a new vga or use the warranty.. something. If the GPU dies/does the freeze, no way you can get out of that. – Shiki May 26 '10 at 19:04

Additional info: to restart the X-server you could go to a virtual console with ctrl + alt + f2, login, and then use: sudo /etc/init.d/gdm restart

More about virtual consoles: Linux / UNIX: Virtual consoles

share|improve this answer
Unfortunately I can't get to the virtual consoles when the freeze occurs :( – Bryce Thomas May 26 '10 at 16:35
Here you have to do this: sudo service gdm restart – Shiki May 26 '10 at 19:03
then try do to this: Alt + SysRq + r that takes keyboard and mouse control from the X server. This is a Magic SysRq Key that permits to give commands directly to the kernel, and it's enabled by default on ubuntu. After typing that you could retry to hit ctrl + alt + f2 :) – Likso May 27 '10 at 8:14
@Shiki - I can't get to a console to do that unfortunately. @Likso - I'll give that a try next time it freezes up. – Bryce Thomas May 28 '10 at 14:09

It turns out that it was indeed my video card causing it to freeze up. After switching it with a replacement video card, I've had no problems in several weeks.

share|improve this answer
Don't hesitate to accept your own answer, if it contains the solution to your problem. – Gnoupi Aug 14 '10 at 12:31

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.