Linux Run-Levels


When you boot a computer running Linux, it will boot into a default runlevel (this is usually level 3 or level 5). There are six different runlevels most Linux distributions use, the following runlevels are defined by default under Red Hat Enterprise Linux:

	0 - Halt the system
	1 - Single-user text mode
	2 - Not used (user-definable)
	3 - Full multi-user text mode (no display manager)
	4 - Not used (user-definable)
	5 - Full multi-user with graphical mode (GUI)
	6 - Reboot the system

Run levels 1 and 2 are not often used.
Most Linux systems run in runlevel 3 or 5.
Most desktop Linux systems boot into runlevel 5 by default and the user is greeted by a graphical login prompt.
Most server Linux systems boot into runlevel 3 by default and the user is greeted by a text-mode login prompt.


Useful Links

For further information see the following links. For the full story consult the manual (man) pages for your distribution.


URLSummary/Description
http://en.wikipedia.org/wiki/Runlevel General overview
http://www.redhat.com/docs/manuals/linux/RHL-7.2-Manual/ref-guide/s1-init-boot-shutdown-init.html Red Hat Reference manual
http://www.centos.org/docs/5/html/Installation_Guide-en-US/s1-boot-init-shutdown-sysv.html CentOS Installation Guide
http://www.iodynamics.com/education/runlevel.html The Linux Runlevel