-r     Requests that the system be rebooted after it has been brought down.

-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.

-H     Requests that the system be halted after it has been brought down.

-P     Requests that the system be powered off after it has been brought down.

-c     Cancels a running shutdown.  TIME is not  specified  with  this  option,  the  first  argument  is
       MESSAGE.

-k     Only send out the warning messages and disable logins, do not actually bring the system down.