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The NTP program is configured using either the
file depending on what distribution of Linux you have. I won't go
into too much detail on how to configure NTP. Instead I'll just
cover the basics.
The most basic ntp.conf file will simply list 2 servers, one that it wishes to synchronize with, and a pseudo IP address for itself (in this case 127.127.1.0). The pseudo IP is used in case of network problems or if the remote NTP server goes down. NTP will synchronize against itself until the it can start synchronizing with the remote server again. It is recommended that you list at least 2 remote servers that you can synchronize against. One will act as a primary server and the other as a backup.
You should also list a location for a drift file. Over time NTP will "learn" the system clock's error rate and automatically adjust for it.
NTP slowly corrects your systems time. Be patient! A simple test is to change your system clock by 10 minutes before you go to bed and then check it when you get up. The time should be correct.
Many people get the idea that instead of running the NTP daemon, they should just setup a cron job job to periodically run the ntpdate command. There are 2 main disadvantages of using using this method.
The first is that ntpdate does a "brute force" method of changing the time. So if your computer's time is off my 5 minutes, it immediately corrects it. In some environments, this can cause problems if time drastically changes. For example, if you are using time sensitive security software, you can inadvertently kill someones access. The NTP daemon slowly changes the time to avoid causing this kind of disruption.
The other reason is that the NTP daemon can be configured to try to learn your systems time drift and then automatically adjust for it.