ntp for linux

http://www.geekride.com/how-to-change-time-date-linux-hardware-clock/
http://support.ntp.org/bin/view/Servers/NTPPoolServers

# ntpdate "server name or IP address"
Now update the hardware clock also.
# hwclock --systohc
To keep your system always updated you can create a cronjob which could run on daily basis and put this:
# ntpdate "server" && hwclock -w
***-w == --systohw

server 0.pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org
server 3.pool.ntp.org