unix 关机命令

安全关机一般使用 shutdown，如shutdown -y -g0 -i0
参数：
    -y    自动应答请求，不需要人工干预
    -g    后接秒数，定义关机延迟的时间，0为立即
    -r    重启，相当于i6
    -i    定义关机状态，有如下几种：

0 (也就是我们俗称的 ok mode, 不会power off) 
Go into firmware. 

1 
Put the system in system administrator mode. All local file systems are mounted. Only a small set of essential kernel processes are left running. This mode is for administrative tasks such as installing optional utility packages. All files are accessible and no users are logged in on the system.

2 
Put the system in multi-user mode. All multi-user environment terminal processes and daemons are spawned. This state is commonly referred to as the multi-user state.

3 
Extend multi-user mode by making local resources available over the network.

4 
Is available to be defined as an alternative multi-user environment configuration. It is not necessary for system operation and is usually not used.

5 (关机,power off)
Shut the machine down so that it is safe to remove the power. Have the machine remove power, if possible.

6 (reboot 重启) 
Stop the operating system and reboot to the state defined by the initdefault entry in /etc/inittab

S, s 
Enter single-user mode.