The default behavior of shutdown is usually to schedule shutdown for one minute.
Cancel a pending shutdown.
Schedule a shutdown for 11 PM.
Schedule a shutdown for 15 minutes from now.
shutdown +5 "Save now!"
Shutdown in 5 minutes and broadcast the message "Save now!" to all terminals.
Halt the machine. This is traditionally a drastic type of shutdown similar to a hard power-off. However, this may be implemented as a normal and immediate shutdown.
Poweroff the machine with shutdown. This is usually the default but can be specified to remove any ambiguity.
Reboot the machine.
Halts the machine without notifying any processes. This is perhaps the most immediate and drastic way to halt a linux box. The -f stands for force.
Another command to power-off a linux box. Accepts the -f flag for a forced power-off.
Reboot the box. Accepts the -f flag. Does not allow for a scheduled reboot as with the shutdown command.