kernel init

  • Boot your system to the grub menu. ESC
  • Edit the menu entry with E
  • Add at the line starting with linux this:
    init=/bin/bash
  • Type the function key to boot.
  • Now at the bash session remount the root filesystem writeable:
    mount -n -o remount,rw /

    Now you have root .... careful now

Surely dangerous, remember though - you must have physical access to the machine to do things like this.