Unix System V-style implement conventionally 7 runlevels. This runlevel implementation vary across many Linux distribution. Usually runlevel 0, 1 and 6 are the same.
Debian distribution has it runlevel 2-5 dedicated to full multi-user with graphical managers and console login whereas Redhat/Fedora has two separate runlevels for each mode. To check the runlevel of you system you can use runlevel command with no arguments:
another way to check your runlevel is to use:
$ who -r
To see what services are starting during which runlevel you can use:
The same command also allows you to turn off and on each service for any particular runlevel. For example to run apache2 on level 2 you will use command:
# chkconfig apache2 2