shutdown- brings the system down
shutdownarranges the system to be brought down in a safe way. You can specify a time with most options, which is assumed to be in seconds. The most common time provided is 'now', which brings the system down without any delay.
Once the specified time has elapsed,
rebootcommand to reboot/poweroff the computer.
--help: prints the help for this command in the terminal
-r <time>: reboots the system once the specified time has elapsed
-h <time>: powers off the system once the specified time has elapsed