The idea behind SysV init runlevels revolves around the idea that different systems can be used in different ways. For example, a server runs more efficiently without the drag on system resources created by the X Window System. Or there may be times when a system administrator may need to operate the system at a lower runlevel to perform diagnostic tasks, like fixing disk corruption in runlevel 1.
The characteristics of a given runlevel determine which services are halted and started by init
. For instance, runlevel 1 (single user mode) halts any network services, while runlevel 3 starts these services. By assigning specific services to be halted or started on a given runlevel, init
can quickly change the mode of the machine without the user manually stopping and starting services.
The following runlevels are defined by default under Fedora:
-
0
— Halt
-
1
— Single-user text mode
-
2
— Not used (user-definable)
-
3
— Full multi-user text mode
-
4
— Not used (user-definable)
-
5
— Full multi-user graphical mode (with an X-based login screen)
-
6
— Reboot
In general, users operate Fedora at runlevel 3 or runlevel 5 — both full multi-user modes. Users sometimes customize runlevels 2 and 4 to meet specific needs, since they are not used.
The default runlevel for the system is listed in /etc/inittab
. To find out the default runlevel for a system, look for the line similar to the following near the top of /etc/inittab
:
id:5:initdefault:
The default runlevel listed in this example is five, as the number after the first colon indicates. To change it, edit /etc/inittab
as root.
Warning
Be very careful when editing /etc/inittab
. Simple typos can cause the system to become unbootable. If this happens, either use a boot diskette, enter single-user mode, or enter rescue mode to boot the computer and repair the file.
For more information on single-user and rescue mode, refer to the chapter titled Basic System Recovery in the Red Hat Enterprise Linux Deployment Guide.