Shutdown command:
shutdown -h now（立刻进行关机）
halt（立刻进行关机）
poweroff（立刻进行关机）
Restart command:
shutdown -r now（现在重新启动计算机）
reboot（现在重新启动计算机）
the difference:
Shutdown -h now and shutdown -r now must be the root user or a user with root privileges,
while halt and reboot can be used by any user in the Linux system without root privileges.
connect:
halt has the same function as poweroff.
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Original link: https://blog.csdn.net/justdb/article/details/7386190