http://raspberrypi.tomasgreno.cz/ntp-client-and-server.html

Problem with storing actual time is partially solved by fake-hwclock package which writes actual time to text file every hour and at system reboot. At start, if no better source of time is present, time is set to one stored in that text file. Since RPi is disposing a RJ-45 port, we can use it as very precise time source within NTP. First we have to install package called ntp.

    apt-get install ntp