Run level

debian的runlevel級別定義如下：
0 - Halt
1 - Single
2 - Full multi-user with display manager (GUI)
3 - Full multi-user with display manager (GUI)
4 - Full multi-user with display manager (GUI)
5 - Full multi-user with display manager (GUI)
6 - Reboot

而redhat的runlevel級別定義如下：
0 - Halt
1 - Single
2 - Not used/User definable
3 - Full multi-user NO display manager
4 - Not used/User definable
5 - Full multi-user with display manager (GUI)
6 - Reboot

You can modify your default run-level:
1. Ubuntu: edit /etc/event.d/rc-default
2. Redhat: edit /etc/inittab