Halt  notes  that  the  system  is  being  brought  down  in  the  file
       /var/log/wtmp, and then either tells the  kernel  to  halt,  reboot  or
       poweroff the system.

       If  halt or reboot is called when the system is not in runlevel 0 or 6,
       in other words when it’s running normally,  shutdown  will  be  invoked
       instead  (with  the  -h  or -r flag). For more info see the shutdown(8)
       manpage.

       The rest of this manpage describes the behaviour in runlevels 0 and  6,
       that is when the systems shutdown scripts are being run.