Shutting Down from Command Line

To reboot your system, you can use the shutdown command, which is found under the /sbin directory (to execute the shutdown command you must be root).  The shutdown command has several command-line options. use -r followed by now to reboot your system immediately (you can also reboot by using the Ctrl+Alt+Del key combination). 

shutdown -r now

You can change the now keyword to a number specifying the time in seconds when you want Linux to reboot. another options is the -h or halt to shutdown you system.  as with the -r option, -h also followed by another option specifying the time when you want Linux to shut down.

shutdown -h now

You can also use the poweroff command to turn off your system immediately. You can execute poweroff without becoming the root.