Linux’s runlevels are:

From Wikipedia:

The term runlevel refers to a mode of operation in one of the computer operating systems that implement Unix System V-style initialization. Conventionally, seven runlevels exist, numbered from zero to six; though up to ten, from zero to nine, may be used.

Depending on your distribution runlevels may differ

Whick runlevel am I in?

So, to find out which runlevel are you In just run:

who -r

You will get something like this:

run-level 3  2010-12-11 21:09    last=S