Originally posted by Thymox
I can't remember what 1, 2 or 4 are used for.
I think I can enlighen you there a little bit:
# Runlevel 0 is halt.
# Runlevel 1 is single-user.
# Runlevels 2-5 are multi-user.
# Runlevel 6 is reboot.
What is done in the runlevels 2 to 5 is not really the same through the different distributions, although 2 sometimes is multiuser without network, 3 is with networking and 5 with graphical login. Something similar can be found in some of the distributions, but that's not really standardized yet to my knowledge...