"A Magic SysRq Key lets you send some low level commands independent of the system state. This means that if the system is frozen you can use these key combinations to perform certain actions and thus regain control.
So what’s the magic? Well if you are ever stuck with an unresponsive system try
Alt+PrintScreen+r+s+e+i+u+b.
Pheew! So how many hands do you need to do this? Or should you use your toes?"
