Rebooting means booting the system again. This can be accomplished by first shutting it down completely, turning power off, and then turning it back on. A simpler way is to ask shutdown to reboot the system, instead of merely halting it. This is accomplished by using the -r option to shutdown, for example, by giving the command shutdown -r now. You can also use the reboot command (which, like halt, doesn't wait until it perpetrates its foul deed).