How do I change the runlevel for a system without rebooting?

To change the runlevel for a system without rebooting or changing the /etc/inittab file, execute the following command as the root user:

telinit With having the following values:

0 ? Halt

1 ? Single-user mode

2 ? Not used (user-definable)

3 ? Full multi-user mode

4 ? Not used (user-definable)

5 ? Full multi-user mode (with an X-based login screen)

6 ? Reboot