Creating a new runlevel or Modifying an existing  runlevels are fun . After reading the following u can master the runlevel concept .

1st to know what is a runlevel and where it is used ?

Runlevel is a system state in which some services are started and some are killed according to the need . Runlevel is controlled by the the parent process “INIT” . Like there are 6 run levels bydefault in any Linux.Unix systems as follows ;

Runlevel 0 – init 0 – halt – used to halt a system

Runlevel 1 – init 1 – Single User Mode – Used for system maintainnance like backup etc. and in this the network services are stopped and only single user can logged in to a system for the maintainnance .

Runlevel 2 – init 2 – Same as runlevel 3 but without NFS

Runlevel 3 – init 3 – Full multiuser mode with networking but without  X11 i.e. GUI  is absent .

Runlevel 4 – init 4 – Reserved for future purpose or u can edit this to create ur own runlevel

Runlevel 5 – init 5 – Full multiuser with X11 support

Runlevel 6 – init 6 – Used for Reboot

This runlevel concept is usually used in all Linux machines as well as Unix machines .

In linux the file /etc/inittab stores the default runlevelin the line

id:1:initdefault:

We can change our runlevel as our need in the above line but 0 and 6 should not be mentioned as default runlevel .