Understanding the shutdown command in Linux

Normally, when you want to shut down or restart your machine, you will run one of the following commands:

shutdown will plan a time for the system to shut down. It can be used to stop, shut down, and restart the machine.

You can specify a time string (usually now or hh:mm to specify hours/minutes) as the first parameter. Additionally, you can set up a broadcast message to be sent to all logged in users before the system is shut down.

Important: If the time parameter is used, the /run/nologin file will be created 5 minutes before the system is shut down. to ensure that no one can log in anymore.

shutdown command example:

# shutdown
# shutdown now
# shutdown 13:20  
# shutdown -p now  ### 关闭机器
# shutdown -H now  ### 停止机器      
# shutdown -r09:35 ### 在 09:35am 重启机器

To cancel an upcoming shutdown, just enter the following command:

# shutdown -c

haltNotify the hardware to stop all CPU functions, but still keep power on. You can use it to keep your system in a low-maintenance state.

Note that in some cases it will shut down the system completely. The following is an example of the halt command:

# halt             ### 停止机器
# halt -p          ### 关闭机器
# halt --reboot    ### 重启机器

poweroff will send an ACPI signal to notify the system to shut down.

The following is an example of the poweroff command:

# poweroff           ### 关闭机器
# poweroff --halt    ### 停止机器
# poweroff --reboot  ### 重启机器

reboot Notifies the system to restart.

# reboot           ### 重启机器
# reboot --halt    ### 停止机器
# reboot -p        ### 关闭机器

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