Happy user of 12.04 desktop since its released, but recently - past couple of months my UI randomly freezes.

Mouse pointer moves, but can not click Keyboard is completely gone Screen painting looks normal - no other display aberrations.

Ctrl-Alt f2/f3 etc work fine and I can use keyboard on terminal prompt, however if I get back to UI display using Ctrl-Alt f7, nothing works. Looks like lightdm or something underneath looses connections with peripheral. Without knowing too much internals, I am thinking it can not be any lower than that since keyboard work on terminals.

There are no log entries of anything crashing in syslog, kern.log and dmesg.

Restarting lighdm forces logout from ui. I can log in after entering my credentials, but after that nothing works.

Is there a way to gracefully restart whatever is causing the problem so that I don't have restart my machine. I really hate to loose all my unsaved work especially when crash happens on something innocent like right on eclipse menu.

Normally noticed the crash when displaying eclipse context menu - right click on some eclipse view. But not everytime. Might be because I spent lot of time in eclipse.


I recently had a similar problem. I'm on Ubuntu 14.04 so the problem may have been completely different from yours, but I was able to fix it by re-installing Unity (Ubuntu's default desktop environment).

To be honest I don't remember exactly which commands I used, but here are a few threads that were useful to me while troubleshooting this problem:

How do I reinstall Unity?

Reinstall `ubuntu-desktop` after removing Gnome

The first answer here is useful as well:

How to reinstall unity desktop on Ubuntu 14.04

I remember using apt to check for missing dependencies and that there were few related to Unity.

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I think you want the old Ctrl+Alt+Backspace command enabled, to restart X. See this question for more info, it's basically:

  1. In a terminal, enter sudo dpkg-reconfigure keyboard-configuration
  2. press Enter 5 times to skip unrelated questions
  3. until the "Terminate the X server with Control+Alt+Backspace" question, and set to Yes.

If you can get to another TTY/terminal (Ctrl+Alt+F2, etc) you could kill the window/display manager (I"m not sure which ones you're using, different versions are available for XFCE/Xubuntu, Unity, gnome shell, etc) and should be able to restart it from there, somehow... maybe a lightdm --replace?

  • Best preventative advice would be to save often, and set up auto-saves. Works for every OS too
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  • I am using Ubuntu 12.04 which I believe uses lighdm. Agree with save advice, but its not always saveable - like forms in the browsers or other applications. What's most annoying is on terminal it works but not in UI – user871199 Jan 22 '15 at 17:14

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