19.1. Runlevels

19.1. 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:

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.

To change the runlevel immediately, use the command telinit followed by the runlevel number. You must be root to use this command. The telinit command does not change the /etc/inittab file; it only changes the runlevel currently running. When the system is rebooted, it continues to boot the runlevel as specified in /etc/inittab.


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