Most users run X from runlevels 3 or 5. Runlevel 3 places your system in multi-user mode with full networking capabilities. The machine will boot to a text-based login prompt with all necessary preconfigured services started. Most servers are run in runlevel 3, as X is not necessary to provide any services utilized by most users. Runlevel 5 is similar to runlevel 3, except that it automatically starts X and provides a graphical login screen. Many workstation users prefer this method because it never forces them to see a command prompt.
The default runlevel used when your system boots can be found in the /etc/inittab file. If you have a line in that file that looks like id:3:initdefault:, then your system will boot to runlevel 3. If you have a line that looks like id:5:initdefault:, your system is set to boot into runlevel 5.
As root, change the runlevel number in this file to set a different default. Save the file and restart your system to verify that it boots to the correct runlevel. See the Official Red Hat Linux Administrator’s Guide (Red Hat Press/Wiley, 2003) for more information on runlevels.