When I say crash, it simply means that the whole system freezes and does not respond to any keyboard or mouse input. There are many reasons that can cause Ubuntu to crash. It could be due to hardware incompatibility (especially ATI/Nvidia graphics cards), a software conflict or when you run too many memory intensive applications at the same time.

In the event of a crash, the last thing that you want to do is to press the power off button. You could cause data loss, or even damage to the hard drive as the system could still be writing data to the hard drive

So what should you do if your Ubuntu crashes? Here are four things that you can do:

1) Force Quit

If you are only experiencing application freeze, go to System-> Administration -> System Monitor. On the Processes tab, select the application name from the list of processes and select ‘End Process‘. If it does not work, right click on the application and select ‘Kill Process‘.

Alternatively, if you anticipate your applications to crash often, you can place a ‘Force Quit‘ applet on your panel. Right click on any panel and select ‘Add to Panel‘. On the popup window, scroll down until you find ‘Force Quit‘. Click Add. Whenever your application crashes, simply click on the Force Quit icon. The cursor will change to a ‘+‘. Click on the application to kill it.

2) Restart ‘X’

If the whole system comes to a freeze and does not accept any keyboard or mouse input, try to restart ‘X’ by pressing ‘Ctrl + Alt + Backspace‘. This will kill all processes and log you out. If this works, it should bring you to the login screen again.

3) Use MagicSys Key to kill all processes

If the crash is so serious that Ctrl + Alt + Backspace have no effect at all, try pressing the MagicSysKey ‘Alt + SysRq + K’ to kill all processes. The MagicSysKey is a set of keyboard combination that allow the users to perform various low level commands regardless of the system’s state using the SysRq key. In case you are wondering where the SysRq key is, in most keyboard configuration, it is found under the Print Screen button. In some laptop configuration, you might have to press the ‘Fn‘ button to access the SysRq key.

In short, press Alt + SysRq (possibly together with the ‘Fn‘ button) + K to kill all processes.

4) If all the above fail…

Try this MagicSysKey combination. It will sure work.

Press and hold Alt + SysRq, then one by one, press and release the following characters in the respective order: ‘R’ ‘E’ ‘I’ ‘S’ ‘U’ ‘B’. The system will perform a series of tasks and finally reboot the computer, safely.

This method should be used only if all other methods fail. If you have difficulty in remembering the character sequence, just remember the opposite of ‘BUSIER’.