Sunday, April 17, 2005

Linux 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.d, where is the number of the runlevel.

Red Hat Linux uses the following runlevels:

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 configured the X Window System during the Red Hat Linux installation program, you had the option of choosing a graphical or text login screen. If you chose a text login screen, you are operating in runlevel 3. If you chose 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:


Change the number in this line to the desired runlevel. The change will 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.
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