Runlevels

Linux utilizes what is called "runlevels". A runlevel is a software configuration of the system that allows only a selected group of processes to exist. Init can run the system in one of eight runlevels. These runlevels are 0-6 and S or s. The system runs in only one of these runlevels at a time. Typically these runlevels are used for different purposes. Runlevels 0, 1, and 6 are reserved. For Redhat Linux version 6, the runlevels are:

0 - halt
1 - Single user mode
2 - Multiuser, without NFS (The same as 3, if you don't have networking)
3 - Full multiuser mode
4 - unused
5 - X11
6 - Reboot

在大多數(shù)Linux操作系統(tǒng)下一共有如下7個典型的運行級別：

0 停機，關機
1 單用戶，無網(wǎng)絡連接，不運行守護進程，不允許非超級用戶登錄
2 多用戶，無網(wǎng)絡連接，不運行守護進程
3 多用戶，正常啟動系統(tǒng)
4 用戶自定義
5 多用戶，帶圖形界面
6 重啟