Use the init command to change rune levels:
# init 1
- Runlevel 0 is halt
- Runlevel 1 is single-user
- Runlevels 2-5 are multi-user (some distro uses RUN level 5 to start X [KDE/Gnome])
- Runlevel 6 is for rebooting system
Typing init 3 will move system to run level 3:
# init 3
On most Linux server system default run level is 3 and on most Linux Desktop system default run level is 5. The default run level is defined by the initdefault line at the top of /etc/inittab. So if you wanna change default run level open file /etc/inittab and edit entry initdefault:
# vi /etc/inittab
Set initdefault to 5, so that you can boot to X next time when Linux comes up:
Save file and reboot to see changes.
getty is the program which opens a tty port, prompts for a login name and password (via /bin/login command). Your console displays a login/password prompt at run levels 1 through 6. You can use ALT+F1...ALT+F6 keys to switch console (use CTRL+ALT+F1..F6 under X windows).
However my experience so far is that students get confused with ssh and KDE/Genome Desktop login. SSH logins are handled by sshd server which starts at run level 2/3. KDE/Genome Desktop login are handled by GDM/XDM/KDM display manager which starts at run level 5 (however Debian Linux and some other distro can start them from run level 2 via special rc.d script located in /etc/init.d/gdm)