init shutdown reboot poweroff halt区别

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init

首先看看LINUX系统几种运行级别
# 0 - 停机（千万别把initdefault设置为0，否则系统永远无法启动）
# 1 - 单用户模式
# 2 - 多用户，没有 NFS
# 3 - 完全多用户模式(标准的运行级)
# 4 – 系统保留的
# 5 - X11 （x window)
# 6 - 重新启动 （千万不要把initdefault 设置为6，否则将一直在重启 ）

#init 0 切换到运行级别0
动作为运行如下两个脚本：

[root@limt rc0.d]# pwd
/etc/rc.d/rc0.d
[root@limt rc0.d]# ls -lrt S*
lrwxrwxrwx. 1 root root 14 Jun 16  2013 S01halt -> ../init.d/halt
lrwxrwxrwx. 1 root root 17 Jun 16  2013 S00killall -> ../init.d/killall

#init 6 切换到运行级别6
动作为运行如下两个脚本：

[root@limt rc6.d]# pwd
/etc/rc.d/rc6.d
[root@limt rc6.d]# ls -lrt S*
lrwxrwxrwx. 1 root root 14 Jun 16  2013 S01reboot -> ../init.d/halt
lrwxrwxrwx. 1 root root 17 Jun 16  2013 S00killall -> ../init.d/killall

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shutdown

shutdown - bring the system down
shutdown [OPTION]... TIME [MESSAGE]
   -r     Requests that the system be rebooted after it has been brought down.
   -h     Requests that the system be either halted or powered off after it has been brought down, with the choice
          as to which left up to the system.
   -H     Requests that the system be halted after it has been brought down.
   -P     Requests that the system be powered off after it has been brought down.
   -c     Cancels a running shutdown.  TIME is not specified with this option, the first argument is MESSAGE.
   -k     Only send out the warning messages and disable logins, do not actually bring the system down.

#shutdown -r 等同reboot，它在系统关闭之前给系统上的所有登录用户提示一条警告信息，然后调用init 6
#shutdown -H 等同halt 它在系统关闭之前给系统上的所有登录用户提示一条警告信息，然后调用init 0
#shutdown -P 等同poweroff 它在系统关闭之前给系统上的所有登录用户提示一条警告信息，然后调用init 0

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reboot,poweroff,halt

reboot,poweroff,halt实际为一个命令，后两者为reboot的链接

[root@limt rc0.d]# ls -lrt /sbin/reboot
-rwxr-xr-x. 1 root root 14832 3月  20 2012 /sbin/reboot
[root@limt rc0.d]# ls -lrt /sbin/poweroff 
lrwxrwxrwx. 1 root root 6 6月  16 2013 /sbin/poweroff -> reboot
[root@limt rc0.d]# ls -lrt /sbin/halt 
lrwxrwxrwx. 1 root root 6 6月  16 2013 /sbin/halt -> reboot

不带--force参数的reboot实际是调用shutdown名，带--force参数的reboot直接关机