sudo apt-get install ntp
sudo service ntp status # should get following result
* NTP server is running
Now when I go back to the “Time and Date” utility, “Configuration:” is (finally) set to “keep synchronized with the Internet servers”
Reference: http://www.tecmint.com/how-to-synchronize-time-with-ntp-server-in-ubuntu-linux-mint-xubuntu-debian/