This is not a joke. It is possible to shut down your crashed linux box safely. It is possible to perform various low level commands regardless of the system’s state.

To perform such a command you have to press Alt + SysRq (Print) + a key representing the command.

To shutdown your box safely use the following combo:

  1. Alt + SysRq + R – takes the keyboard out of raw mode.
  2. Alt + SysRq + E – terminates all processes (except init).
  3. Alt + SysRq + I – kills all processes (except init).
  4. Alt + SysRq + S – synchronizes the disk.
  5. Alt + SysRq + U – remounts all filesystems read-only.
  6. Alt + SysRq + B – reboots the machine.

More details can be found at Wikipedia.