Run with Run Levels

A runlevel is a software configuration on the Linux system that allows only a selected group of processes to exist.
The “init” is the parent of all processes with PID 1. It’s primary purpose it to spawn(call forth) processes from a script stored in the “/etc/inittab” file. Init can be in any of the following runlevels:

  • Runlevel 0 => Halt/Shutdown
  • Runlevel 1 => Single User Mode(root)
  • Runlevel 2 => Multi-user mode without networking
  • Runlevel 3 => Multi-user mode with networking
  • Runlevel 4 => Unused
  • Runlevel 5 => X11
  • Runlevel 6 => Reboot

Find out the current run level
Type the following command:

$ who -r
          run level 5 2011-11-11 18:53       last=3

Current runlevel is 5 and the last run level was 3.
The same information can be obtained from the “runlevel” command.

$ runlevel
3 5

Change the runlevel
The “init” command is used to change the runlevel.
For example “init 3” will move the system into runlevel 3.

# init 3

On most Linux servers the default runlevel is 3, whereas the Linux desktop systems default to runlevel 5. To change the default runlevel, edit the “initdefault” entry in the /etc/inittab file.


# vi /etc/inittab

Save and close the file(zz). Reboot the system to see the changes.

About Deepak Devanand

Seeker of knowledge
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