If you use Ubuntu 16.04 or Ubuntu-Debian derivatives and above, systemd provides an easier way to do time synchronization to time server.
First you have to install ntdate package:
sudo apt install ntpdate
Secondly, you have to edit /etc/systemd/timesyncd.conf and add your prefered time server to sync to:
[Time]
NTP=0.asia.pool.ntp.org
FallbackNTP=ntp.ubuntu.com
Save the file and restart the time synchronization service:
sudo systemctl restart systemd-timesyncd
To check the status:
sudo systemctl status systemd-timesyncd
