Runlevels in red hat enterprise linux

Runlevels:

A runlevel is a state, or mode, that is defined by the services listed in the directory /etc/rc.d/rc<x>.d, where <x> is the number of the runlevels. The following runlevels exist:

0 — Halt
1 — Single-user mode
2 — Not used (user-definable)
3 — Full multi-user mode
 4 — Not used (user-definable)
5 — Full multi-user mode (with an X-based login screen)
6 — Reboot
If you use a text login screen, you are operating in runlevel 3. If you use a graphical login screen, you are operating in runlevel 5. The default runlevel can be changed by modifying the /etc/inittab file, which contains a line near the top of the file similar to the following:
id:5:initdefault:
Change the number in this line to the desired runlevel. The change does not take effect until you reboot the system.