Runlevels

Before you can configure access to services, you must understand 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 runlevel.

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.