Runlevels

A runlevel is a set of services that can be started and stopped together. E.g. SUSE and Red Hat Linux define the following runlevels:
 * 1 : single-user
 * 2 : multi-user, no network
 * 3 : multi-user, with network
 * 4 : not defined
 * 5 : multi-user, network with graphics
 * 6 : no runlevel, used to reboot

This means for example that runlevel 3 includes the service network.

You can find out your current runlevel with the command runlevel You can change your runlevel with the command init runlevel where runlevel is a number from 1 to 6.

When you boot a Linux system, you can hand over the runlevel you want to boot into as a kernel parameter. See boot process. If you do not use a kernel parameter, the system will look for the configuration in /etc/inittab.

The services itself are system V initscripts.