Linux system shutdown at specified time and prompts the user

1. Common commands shutdown:
   the shutdown
   poweroff
   the HALT
   the init 0
2. To achieve prompt the user during shutdown, the general shutdown command
   specified time Shutdown:
   If the designated 20:30 off
   
   directly shutdown plus the time to complete the task at the specified time off
   can also add -h parameter
   
3. Specified time and prompts the user to shut down:
   
4. Cancel the shutdown: