GNU magic keys
If GNU system is not responding (for whatever reason which could be analysed through the system logs), there are different combinations of keys which allow taking control of the system back. It is the magic keys, a combination of keys which are usually activated in all distributions. The system petition function is usually assigned to the Print Screen key. Alt+PrintScreen+: r: it takes control of the keyboard in an X system. Many times it is the X system itself which causes the system freeze. After Alt+PrintScreen+r, the combination Ctrl+Alt+Backspace can be tried to log out of X. s: writes data to the hard disk cache. e: sends the SIGTERM signal to all processes but init. i: sends the SIGKILL signal to all processes but init. u: remounts the whole filesystem in read-only mode, to ensure a safe reboot. b: reboots the system. These are the classical well-known combinations, but there are other magic combinations which can be useful in other situations: ...