On Thu, Jun 08, 2017 at 05:09:49PM -0500, Michael Schwager wrote: > Hello, > Is it possible to get clock accuracy in the microseconds using chrony and a > local time server?
Yes, that should be possible. > I have tried with ntpd and the best I have seen is 5 ms accuracy (according > to ntpstat). I have tweaked polling intervals but still the best is 5 ms. What polling interval have you tried? ntpstat reports the NTP root distance, which includes delay and dispersion accumulated from the stratum 0 time source down to the client. The problem may be with the server. If it is reporting a large root delay or dispersion, it doesn't matter how stable and symmetric is the network delay or what the client does, the distance reported by the client will be always large. You can check the root delay and dispersion of the server with "ntpq -c as -c 'rv &1'" or "chronyc ntpdata". The distance gives you the maximum estimated error. If it's 5 milliseconds, it doesn't mean the actual error of the clock is 5 milliseconds. It's more likely just few tens or hundreds of microseconds. With a decent server and a sufficiently short polling interval it should be closer to the former. BTW, PTP doesn't have anything like that and generally PTP slaves cannot estimate their maximum error. > In short: The business wants microsecond accuracy today and PTP will have > to wait on CentOS 7 which will be a couple of weeks down the road due to > our development priorities. Note that in 7.4 will be chrony-3.1, which supports HW timestamping. If you don't have switches with PTP support and the NIC on the machine can timestamp all packets (not just PTP packets), NTP might work better for you. -- Miroslav Lichvar -- To unsubscribe email chrony-users-requ...@chrony.tuxfamily.org with "unsubscribe" in the subject. For help email chrony-users-requ...@chrony.tuxfamily.org with "help" in the subject. Trouble? Email listmas...@chrony.tuxfamily.org.