For example, runlevel 3 is configured in mainstream distributions such as Red Hat, Fedora Core and SuSE to provide full multi-user capabilities with networking and a text-based interface. Runlevel 5 is the same as runlevel 3, but with an additional step of loading a graphical user interface for the user. Many servers are configured to boot into runlevel 3 as part of their normal operation, since they don’t need a GUI to do their job.

The concept of the plumbing behind runlevels is easy to understand. Generally speaking, there is a collection of programs used to start up a machine (and another set of programs that are run during machine shutdown). Different runlevels invoke subsets of these programs. The definition of which programs are included in one runlevel’s subset versus another’s are contained in a series of directories named /etc/rcN.d, where N runs from 0 to 6, matching the various runlevels available. Thus, the program that starts the GUI, startx, is included in /etc/rc5.d, but not in /etc/rc3.d

Getting Linux to load to a text interface
So, you want to boot Linux into runlevel 3 because all you need is a text based interface. When Linux boots up, one of the things it does early on in the process is look in a file called /etc/inittab for a line that looks like this:
id:5:initdefault:

The number after the first colon defines which runlevel will be used during startup. In this example, the ‘5′ in this line (this is an inittab file from a Fedora Core machine) indicates that the machine will be booted to the GUI, with multi-user functionality and networking. The other runlevels and their corresponding numbers for Fedore Core as are follows (this block of text comes directly out of the comments in the inittab file - your distribution will likely have similar comments indicating what each of the runlevels stands for)

Download pdf From GUI to Text: A Windows User’s Guide to Running Linux without a GUI