Linux命令之shutdown

shutdown命令安全地将系统关机。 有些用户会使用直接断掉电源的方式来关闭linux，这是十分危险的。因为linux与windows不同，其后台运行着许多进程，所以强制关机可能会导致进程的数据丢失﹐使系统处于不稳定的状态﹐甚至在有的系统中会损坏硬件设备。可用man shutdown来了解命令的详细使用。

SHUTDOWN()                                      shutdown                                     SHUTDOWN()

NAME
       shutdown - Halt, power-off or reboot the machine

SYNOPSIS
       shutdown [OPTIONS...] [TIME] [WALL...]

DESCRIPTION
       shutdown may be used to halt, power-off or reboot the machine.

       The first argument may be a time string (which is usually "now"). Optionally, this may be followed
       by a wall message to be sent to all logged-in users before going down.

       The time string may either be in the format "hh:mm" for hour/minutes specifying the time to
       execute the shutdown at, specified in 24h clock format. Alternatively it may be in the syntax "+m"
       referring to the specified number of minutes m from now.  "now" is an alias for "+0", i.e. for
       triggering an immediate shutdown. If no time argument is specified, "+1" is implied.

       Note that to specify a wall message you must specify a time argument, too.

       If the time argument is used,  minutes before the system goes down the /run/nologin file is
       created to ensure that further logins shall not be allowed.

OPTIONS
       The following options are understood:

       --help
           Print a short help text and exit.

       -H, --halt
           Halt the machine.

       -P, --poweroff
           Power-off the machine (the default).

       -r, --reboot
           Reboot the machine.

       -h
           Equivalent to --poweroff, unless --halt is specified.

       -k
           Do not halt, power-off, reboot, just write wall message.

       --no-wall
           Do not send wall message before halt, power-off, reboot.

       -c
           Cancel a pending shutdown. This may be used cancel the effect of an invocation of shutdown
           with a time argument that is not "+0" or "now".

EXIT STATUS
       On success,  is returned, a non-zero failure code otherwise.

SEE ALSO
       systemd(), systemctl(), halt(), wall()

systemd                                                                                    SHUTDOWN()

从man page可知道：shutdown被用来暂停、关闭、重启机器。shutdown后面有3个参数，都是有[]，说明都是可选参数。在DESCRIPTION里了解到，如果未指定TIME参数，那就意味着默认配置“+1”，单位为分钟。如果TIME参数为now，那就意味着时间配置为“+0”，单位为分钟。时间也可设置为"hh:mm" = hour/minutes进行操作。

命令参数说明：

--help：帮助
-H/--half：关闭机器
-P/--poweroff：关闭机器
-r/--reboot：重启机器
-h：与--poweroff一样
-k：不暂停、不关闭、不重启机器，只发送消息给在线的用户
--no-wall：暂停、关闭、重启机器前，不发送消息给在线的用户
-c：取消shutdown命令操作

实例：

特定时间执行关机命令

shutdown –h now             //立即关机
shutdown –h :           //在12:00关机

指定五分钟后关机，并发出警告信息

shutdown + “This System will be shutdown in  minutes”
Broadcast message from root@CentOS6.(/dev/pts/) at : …

The system is going down for maintenance in  minutes!                 //系统提醒
This System will be shutdown in  minutes                              //用户自定义提醒

指定3分钟后重启，并发出警告信息

shutdown –r + “3分钟后关机重启”
Broadcast message from root@CentOS6.(/dev/pts/) at : …

The system is going down for reboot in  minutes!          //系统提醒
3分钟后关机重启                                              //用户自定义提醒

给所有登录用户发送提醒，不关闭重启。

[root@CentOS6 桌面]# shutdown –k  “Waring:maybe the system will be shutdown”
[root@CentOS6 桌面]#
Broadcast message from root@CentOS6.(/dev/pts/) at : …

The system is going down for maintenance in  minutes!
Waring:maybe the system will be shutdown