date is a command line utility for printing or setting the system date and time. The base date (epoch) used for calculations and conversions is 00:00:00 UTC on 1 January 1970. Date can also be used to print a given date and time in a variety of formats e.g.
date outputs the current time e.g. Sun Feb 27 16:31:59 GMT 2011
date '+%Y-%m-%d %H:%M:%S' outputs 2011-02-27 16:33:22
date -d @1298824473 adds @ to output Sun Feb 27 16:34:33 GMT 2011
`date -s "Sun Feb 27 16:34:33 GMT 2011" with suitable privilege will set the system date.