What is run level, how many run levels present and how to change run level?

In Linux server mainly 6 types of run level available, each and every run level having its own unique features and if you want to change a run level for your server, than kindly change the run level in /etc/inittab file but before that understand the each and every run level usage.

 0 – halt (Do NOT set initdefault to this)
 1 – Single user mode
 2 – Multiuser, without NFS (The same as 3, if you do not have networking)
 3 – Full multiuser mode
 4 – unused
 5 – X11
6 – reboot (Do NOT set initdefault to this)

To check current run level run “who -r” on shell it will show you current run level set on your server.

root@admin [~]# who -r
run-level 3 2016-07-13 21:19 last=S

To change the run level open a file  /etc/inittab and change the value

From

id:3:initdefault:

To

id:1:initdefault:

In above example, we have changed run level from “3” to “1”,  we can also use following command to change run level

init 1

Let us know, if you have any further queries.