I have a GPS server with NTP output. I want to synchronize the clock on the UNIX server using the NTP output of the GPS.

After changing the UNIX server time manually, UNIX server takes a long time to synch with GPS time. for example if I change the UNIX server time to lag by 2 seconds, it takes approximately 20 minutes to synchronize with GPS time: similarly, if I change the UNIX server time to lag by 1 minutes; it is taking approximately 1 hour to synchronize with the GPS time.

My question, why does UNIX server takes such a long time to synch with GPS after changing the time maually?

  • You may be able to get your computer to sync to the NTP server immediately by rebooting it. – G-Man Aug 21 '14 at 18:18

ntp intentionally slews the system time towards the time provided by its peers in very small increments, to avoid large jumps in time that might upset running processes. Although accurate time keeping is essential for host-to-host communication, even more important is the integrity of the system's own clock.

There are some useful and interesting FAQs about the protocol on the NTP project website.


I use ntpdate -u pool.ntp.org before start or restart local ntpd. This is main part of local /etc/ntpd.conf : server ntp1.vniiftri.ru minpoll 3 iburst burst prefer server ntp2.vniiftri.ru server pool.ntp.org

Most important piece is minpoll 3 iburst: you instruct daemon to send as many packets as possible to sync guaranteed.

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