Для инвалидов там и написано:
> when it's running normally, shutdown will be invoked instead (with the -h or -r flag). For more info see the shutdown(8) manpage.
>> (with the -h or -r flag)

$ man shutdown
> -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.

Ещё раз для инвалидов:
> with the choice as to which left up to the system.