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At this moment my Compiz crashed, and the top bar disappeared, as also Alt + Tab, or the left launcher. So I cant open a terminal (with ctrl+t), or change program that I am using. Im locked into firefox and cant open, reboot or logoff (only on the power button). What can I do?

PS: After I upgraded from 11 to 12.04 my ubuntu is always crashing, lagging more, etc.

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Magic combinations to your rescue. Alt+Printscr+K should mercilessly kill everything and get you back to login screen. –  Mahesh Jun 15 '12 at 13:48
    
thanks. you saved me from prision! =] –  Ricardo Martins Jun 16 '12 at 1:35
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3 Answers 3

Option 1:

Switch to a tty, and do some geeky debugging.
Pressing Ctrl+Alt+F1 through F6 switches to tty1 through tty6 respectively. A tty is a virtual terminal. log in to your account, and in case of a crash, submit a bug report. (Answer by Me)

  • To restart Graphical User Interface - sudo service lightdm restart

    This will log you out in GUI and gets you back to login screen. If you use a non-default display manager, replace lightdm with kdm or gdm as appropriate.

  • In most cases, restarting unity should work. unity --replace

    This will restart just Unity. Any open applications will remain open, and is hence safe and better to try this before restarting DM. If the command exits with 137; retry it. It works. If the command exits with 1, Retrying it will have no effect. It will continue to fail.

    Remember to switch to graphical console on tty7 after running this. (Ctrl+Alt+F7 )

Option 2:

The magic SysRsq combinations are guaranteed to work. there are a whole lot of them, and googling may help.

For now, we are particularly interested in Alt+PrintScr+K, which kills all processes on a tty, so while on tty7 ( the default one with graphics) it kills Xserver and brings you back to login screen.

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what if unity --replace doesn't terminate at all? –  lenz Jun 22 '13 at 7:38
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The old CTRL-ALT+1 opens a text terminal.

From there you can troubleshout or simply issue a shutdown command.

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Switch to terminal number 1 (control+alt+F1) and run

DISPLAY=:0 unity --replace

or

DISPLAY=:0 compiz --replace

Sometimes it doesn't restart; Just kill all compiz processes and try again in case.

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compiz supports the --display flag. So those prefer can run compiz --display :0 --replace instead of DISPLAY=:0 compiz --replace. –  Eliah Kagan Jul 6 '12 at 16:00
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