Run Levels in Linux Operating system


Linux utilizes what is called "runlevels". A runlevel is a software configuration of the system that allows only a selected group of processes to exist. Init can run the system in one of eight runlevels. These runlevels are 0-6 and S or s. The system runs in only one of these runlevels at a time. Typically these runlevels are used for different purposes. Runlevels 0, 1, and 6 are reserved. For Redhat Linux version 6, the runlevels are:
0
-
halt
1
-
Single user mode
2
-
Multiuser, without NFS (The same as 3, if you don't have networking)
3
-
Full multiuser mode
4
-
unused
5
-
X11
6
-
Reboot

1.      level 0 : to halt the system, it reboots the systems again and again after login in
2.      level1 :single user mode, this is a special mode in which only one use ie the super user mode in which limited system based linux commands work.
3.      level2-level5 : this is the multi user mode in which the system works at its full potential with all the command set that it supports
4.      level 6 : entering into this level reboots the system.

Comments

  1. unmatchedenduranceSeptember 8, 2011 at 8:16 AM

    in many distros even the graphics system initializes in Runlevel 3.
    n btw u write "Init can run the system in one of eight runlevels"
    where r the remaining 2 runlevels. at max if u count 0 and 6 u could have 7 yaar.

    ReplyDelete
  2. Hariharan DevarajanSeptember 8, 2011 at 8:50 AM

    the 8 run level mentions is a virtual run level used by initng. And the fact that some boot into graphics mode in init 3 is that they must have edited the file and booted them to graphics mode. I would like to know which all os do that cause i myself did that while making my distro. What i have explained here is the basic way run levels work.

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