Today's commands are how you can check what runlevel your system is in and then change it.

Check the current runlevel:

[[email protected] tmp]# runlevel   
N 5

Change the current runlevel:

[[email protected] tmp]# init <new_level>

The run levels in Unix/Linux are used to define what state init (the parent of all processes) is in. Each distribution of Unix/Linux has different definitions of what run levels starts what processes.

Usually you can find the different definitions in /etc/inittab below is the one from a fedora box.

# Default runlevel. The runlevels used are:  
# 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)