The Network Time Protocol (NTP) is an Internet Standard Recommended Protocol for communicating the Coordinated Universal Time (UTC) from special servers called time servers and synchronizing computer clocks on an IP network.
Time Servers, or time source references, communicate with special time keeping equipment such as Global Positioning System (GPS) receivers, atomic clocks, radios, satellite receivers or modems.
The accuracy of each time server is defined by a number called its stratum. Stratum one servers are those at the top level which communicate directly with a time source such as a GPS or an atomic clock. Each level downwards in the hierarchy is classified as one greater than the preceding level (for example, stratum two, stratum three). Current stratum one servers can provide time within a millisecond's accuracy or better.
For a list of available Stratum 1 and 2 servers consult http://www.ntp.org/
You can get the list of the NTP server based on your region (country) - http://www.pool.ntp.org/en/
OpenSuSe user can install NTP using "1-click" installer - here
The ntp.conf' file is main source of configuration information for a NTP server installation. Amongst other things, it contains a list of reference clocks that the installation is to synchronise. A list of NTP server references is specified with the server' configuration command thus or the same thing can be configure using YAST control center:
Go to Yast → System → Date and Time, click on "Change" button to open up the NTP configuration dialog box.
Provide the name of the appropriate time server located in your region (country) and click on "Accept" save the confguration in your ntp.conf'
Now, start your ntp daemon (/etc/init.d/ntp start) to make sure that your system clock keep getting synchronized with the specified time server.