How to recover from fullscreen crash?

If Control+Alt+F1 works you can use it to drop to a hard terminal. From there you can:

• Try killing the application. I use htop to find and nuke something (sudo apt-get install htop) but you can also just use commands like kill and pkill if you're happy with them. I prefer htop because it lets me see what is schizing out.

  It's then Control+Alt+F7 (sometimes F8 or F9) to return to your X session.

• If that doesn't work (X is still locked up) or the X server is somehow damaged (tons of artefacts, wrong resolution, etc), and I don't have any unsaved work, I'd try restarting gdm (the beast that launches X and manages logins etc).

  sudo restart gdm
  

  That should automatically pull you back into X but all your applications die with X so that's why I say this is really for when you've got nothing open that you should have saved.

If you can't get to a TTY, or SSH in from another system (if you're running a SSH server and have another computer or phone with SSH client) and can't do the above, you might have to try the magic restart keyboard combination. It's somewhat safer than pulling the plug.

Hold Alt + PrintScr/SysRq and then slowly type: r e i s u b

A handy mnemonic for remembering this is: Reboot Even If System Utterly Broken

If that doesn't work, go postal on the power button.

You could try to restart X server by pressing CTRL-ALT-Backspace.

Just make sure that you have enabled the keyboard shortcut from:

System --> Preferences --> Keyboard --> "Layouts" Tab --> Options

You can press ctrlaltF1 to drop to a console. Log in there, and you can kill the offending program. I like to use htop for this.

That said, it's possible that X itself might be wedged. In that case, you'll have to restart GDM:

 sudo service gdm restart

To return to X, press ctrlaltF7.