If you're sitting there at your Linux box looking at a login screen... You can either:
- log in, open a terminal window (there's one somewhere on the menu), su to root and type:
ls -l /sbin/init /sbin/telinit
find / -name init -o -name telinit
- If they don't show the command, log in, open a terminal window, su to root, edit /etc/inittab and reboot (I hate that word)
- From the GUI login screen type <Ctl><Alt><F1> (or 2,3,4,5,6), login as root and try the steps above.