The -u flag is used to display or set the date in GMT (universal) time. yy represents the last two digits of the year; the first mm is the month number; dd is the day number; hh is the hour number (24 hour system); the second mm is the minute number; .ss is optional and represents the seconds. For example:
sets the date to June 13 1985, 4:27 PM. The year, month and day may be omitted; the default values will be the current ones. The system operates in GMT. Date takes care of the conversion to and from local standard and daylight-saving time.
If a network time system is being used to synchronize the clocks of machines on the network, the network time will eventually override the time set locally by date. The recommended network time synchronization daemon is ntpd(8). (However, if instead the old daemon timed(8) is running, date sets the time globally on all the network's machines unless the -n option is given.)
If you try to set the date but are not the super-user, an error message is printed, along with the current (unchanged) date and time.