您可以通过键入以下命令获取有关命令的信息：
man <command>
对于shutdown您获得的命令：
OPTIONS
-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.