You will find lots of tutorials about how to setup NTP server. However if you just wanna synchronize single Linux desktop connected via A/DSL Internet connection use ntpdate command. It is very easy to configure and install ntp client. Following instructions are only compatible with Debian / Ubuntu Linux.
ntpdate sets the local date and time by polling the Network Time Protocol (NTP) server(s) given as the server arguments to determine the correct time. It must be run as root on the local host. A number of samples are obtained from each of the servers specified and a subset of the NTP clock filter and selection algorithms are applied to select the best of these. Note that the accuracy and reliability of ntpdate depends on the number of servers, the number of polls each time it is run and the interval between runs.
Install ntpdate utility
ntpdate command sets the local date and time by polling the Network Time Protocol (NTP) server(s).
# apt-get install ntpdate
You are done by default /etc/default/ntpdate file is use to point pool.ntp.org server .
Allow access to NTP client via Iptables firewall
NTP client uses the udp port 123 to communicate with NTP server. Following rule opens/allows NTP client outgoing request:
# NTP outgoing client request iptables -A output -p udp -s 192.168.1.1 --sport 1024:65535 -d 0/0 --dport 123 -m state --state NEW,ESTABLISHED -j ACCEPT iptables -A input -p udp -s 0/0 --sport 123 -d 192.168.1.1 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT
Add above rules to your existing iptables script. Please note if you have more than 2-3 computers, then it is better idea to setup your own NTP server. I will write on ntpserver configuration later on.
For more information visit public ntp time server for everyone NTP pool website and read ntpdate man page.