Keeping Clocks Synchronized with a Time Server

If you deal with more than a couple of computers on a regular basis, you've no doubt become frustrated with clock drift, which is a computer clock's inability to maintain an accurate time. Clock drift exists for many reasons, but the end result can be maddening, as you attempt to keep all your clocks synchronized. Worse, clock drift can cause serious problems for some network protocols and troubleshooting procedures. These protocols and procedures require clocks on two systems to be synchronized to within a few seconds of each other, at most. For instance, the Kerberos security suite embeds time stamps in its packets, and it relies on this data as a security measure. As a result, if two systems' clocks are set differently, Kerberos may not work. If you're trying to track down a cracker, comparing log files from multiple systems can help, but this procedure is complicated if each system's clock is set differently. For these reasons, Linux supports various methods of synchronizing systems' clocks across a network. One of the most popular of these methods is the Network Time Protocol (NTP). By installing an NTP server on every computer on your network, you can keep the systems' clocks synchronized to each other, with well under a second's difference between them.

Note A typical NTP installation places a server on every computer. In reality, an NTP server functions as both a client and a server, as described shortly. Although there are client-only NTP packages, the full NTP server does the best job of maintaining a system's clock at an accurate value.

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