First and foremost you should be logged in as root.
The /etc folder on these Linux installations contain a file named inittab - mind you no extensions to the filename. This file contains \Nlots lots of important parameters & runlevel configurations that the kernel reads while booting and configures the system accordingly. Open this file in your favourite editor and scroll down just a little bit say, till the 18th-20th line (usually) till you find something similar to this:
# Default runlevel. The runlevels used by RHS are: