According to the generic runlevel specification, you just have to change to runlevel 3. (Typical systems start in runlevel 5 because of the GUI)

Runlevel ID Name Description
0 Halt Shuts down the system
1 Single-User Mode Mode for Administrative Tasks
2 Multiuser Mode Does not configure network interfaces and does not export networks services
3 Multiuser Mode with Networking Starts the system normally
4 not used / user definable For special purposes
5 System starts normally using a graphic interface (GUI) As runlevel 3 +
6 Reboot Reboots the system

to do that, just type the command as root:

# init 3