Linux Changing Run Levels

Posted on in Categories Howto, Linux, Linux desktop last updated October 16, 2005

A question from my email bag:

How do changing run levels affect us or our users?


If you are moving to higher run levels, you may make additional services available to users, while moving to a lower run level will causes to services (daemons) to become unavailable. On the production server run level 3 is the normally used and rarely changed. However, some administrative tasks require the administrator to move system to run level 1 i.e single user mode.

Linux Find Out Current Run Level Command

Type the following command:
$ who -r
Sample outputs:

         run-level 2  2011-10-12 05:38   

Linux Change Run Level Command

Use the init command to change rune levels:
# init 1

Runlevel And Its Usage

The Init is the parent of all processes with PID # 1. Its primary purpose is to create processes from a script stored in the file /etc/inittab file. This file usually has entries which cause init to spawn gettys on each line that users can log in. A runlevel is nothing but a software configuration of the Linux system which allows only a selected group of processes to exist. The processes spawned by init for each of these runlevels are defined in the /etc/inittab file. Init can be in one of eight runlevels as follows:

  • Runlevel 0 is halt
  • Runlevel 1 is single-user
  • Runlevels 2-5 are multi-user (some distro uses RUN level 5 to start X [KDE/Gnome])
  • Runlevel 6 is for rebooting system

For example, typing the init 3 command will move system to run level 3:

# init 3

On most Linux server system default run level is 3 and on most Linux Desktop system default run level is 5. The default run level is defined by the initdefault line at the top of /etc/inittab file under CentOS / Fedora / Redhat / RHEL / Debian Linux. To change the default run level, edit /etc/inittab file, and edit entry initdefault:

# vi /etc/inittab

Set initdefault to 5, so that you can boot to X next time when Linux comes up:

id:5:initdefault:

Save and close the file. Reboot the system to see changes:
# reboot

More About getty

getty is the program which opens a tty port, prompts for a login name and password (via /bin/login command). Your console displays a login/password prompt at run levels 1 through 6. You can use ALT+F1…ALT+F6 keys to switch console (use CTRL+ALT+F1..F6 under X windows).

SSH logins are handled by OenSSH (sshd) server which starts at run level 2/3. KDE/Genome Desktop login are handled by GDM/XDM/KDM display manager which starts at run level 5 (however Debian Linux and some other distro can start them from run level 2 via special rc.d script located in /etc/init.d/gdm)

Related articles:

Updated for accuracy!

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

19 comment

  1. you have some good content! i’m reading this blog since last 4+ months; althoug it is not updated daily like other blog/sites still it makes a good read as it is based upon Linux/UNIX sys admins hard core experince
    considering only 1 or 2 perople contributes to this blog it is a good read and you have Good number of hits as well. Just wanna say good job man & keep it up

    1. RUN-LEVEL IN LINUX
      ==================
      0 – halt (shutdown pc)
      1 – Single user mode
      2 – Multiuser
      3 – Full multiuser mode
      4 – unused
      5 – X11 (Graphical)
      6 – reboot

      TO VIEW RUNLEVEL CONFIG FILE

      # cat /etc/inittab

      TO CHANGE RUNLEVEL CONFIGURATION FILE
      # vi /etc/inittab

      To check Current Run Level
      # who -r or
      # runlevel

      To change Run Level
      # init 1

      On most Linux server system default run level is 3 and on most Linux Desktop system default run level is 5.

  2. Thanks, this really helped me out. It turns out Ubuntu does have both commands, albeit a bit useless due to it lacking a proper single-user bootmode that’s accessible, this still helped. Thanks very much.

  3. For the folks fool enough to edit their /etc/inittab config file to 0 or 6, your only way to break the loop is to boot the system from a livecd, then navigate to the config file through the live filesystem (probably /mnt/sd*/etc/inittab or /media/*) and edit it. But seriously, what were you expecting to happen?

  4. Guignol is actually kind of wrong there. A better option, to me, would to use Grub to boot into a specific runlevel, and then edit the inittab file to fix your mistake.

    Just google “grub change runlevel” and you should get some useful results.

    1. Try to avoid 0 and 6 .. Put 5 for example.

      As someone said before in the documentation:
      0 – halt (shutdown pc)
      1 – Single user mode
      2 – Multiuser
      3 – Full multiuser mode
      4 – unused
      5 – X11 (Graphical)
      6 – reboot

      If you are on 6, the system will reboot on and on.
      If you want to use Linux desktop and graphics try setting runlevel to 5
      If you have a Linux server, try 3
      You can change your runlevel by typing ‘init 5’ from bash cli.
      init 5
      init 3

  5. Under Red Hat Enterprise Linux, it is possible to change the default runlevel at boot time.

    To change the runlevel of a single boot session, use the following instructions:

    When the GRUB menu bypass screen appears at boot time, press any key to enter the GRUB menu (within the first three seconds).

    Press the a key to append to the kernel command.

    Add at the end of the boot options line to boot to the desired runlevel. For example, the following entry would initiate a boot process into runlevel 3:

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