Linux Start up and Run Levels

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

在大多数Linux操作系统下一共有如下7个典型的运行级别:

0 停机,关机
1 单用户,无网络连接,不运行守护进程,不允许非超级用户登录
2 多用户,无网络连接,不运行守护进程
3 多用户,正常启动系统
4 用户自定义
5 多用户,带图形界面
6 重启

推荐阅读更多精彩内容