This article is from the the Brief Linux FAQ (BLFAQ) Maintained by Neil Zanella nzanella@ganymede.cs.mun.ca
There are various ways. The most popular ones are logging in as root and issuing the command "/sbin/shutdown -h now" or "/sbin/halt" to shut it down or "/sbin/shutdown -r now" or "/sbin/reboot" to reboot. On most systems while using a text based console pressing the <ctrl>, <alt> and <del> keys simultaneously will also reboot the system.
 
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