Linux has 6 different runlevels all which have there seperate configuration.
Runlevel – System State
0 – Halt the system
1 – Single-user mode
2 – Multi-user mode (without NFS)
3 – Multi-user mode (cli)
4 – unused/reserved
5 – Multi-user mode, graphical login
6 – Reboot the system
runlevels may vary from distro to distro but this is usually only levels 2 and 4 which are usually reserved.
To change the current runlevel from command line
# init runlevel
Examples
reboot the system.
# init 6
Start a gui when booted into terminal (switching from runlevel 3 to runlevel 5).
# init 5
Shutdown the system.
# init 0
