From 113f2ebec03e7ac331f8b09fdd22107e56013c7e Mon Sep 17 00:00:00 2001 From: Miroslav Lichvar Date: Mon, 21 May 2018 14:49:53 +0200 Subject: [PATCH] doc: add new questions to FAQ --- doc/faq.adoc | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/doc/faq.adoc b/doc/faq.adoc index 5bad34f..95f02dd 100644 --- a/doc/faq.adoc +++ b/doc/faq.adoc @@ -292,6 +292,49 @@ to makestep 1 -1 ---- +=== Using a Windows NTP server? + +A common issue with Windows NTP servers is that they report a very large root +dispersion (e.g. three seconds or more), which causes `chronyd` to ignore the +server for being too inaccurate. The `sources` command may show a valid +measurement, but the server is not selected for synchronisation. You can check +the root dispersion of the server with the ``chronyc``'s `ntpdata` command. + +The `maxdistance` value needs to be increased in _chrony.conf_ to enable +synchronisation to such a server. For example: + +---- +maxdistance 16.0 +---- + +=== Using a PPS reference clock? + +A pulse-per-second (PPS) reference clock requires a non-PPS time source to +determine which second of UTC corresponds to each pulse. If it is another +reference clock specified with the `lock` option in the `refclock` directive, +the offset between the two reference clocks must be smaller than 0.2 seconds in +order for the PPS reference clock to work. With NMEA reference clocks it is +common to have a larger offset. It needs to be corrected with the `offset` +option. + +One approach to find out a good value of the `offset` option is to configure +the reference clocks with the `noselect` option and compare them to an NTP +server. For example, if the `sourcestats` command showed + +---- +Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev +============================================================================== +PPS0 0 0 0 +0.000 2000.000 +0ns 4000ms +NMEA 58 30 231 -96.494 38.406 +504ms 6080us +foo.example.net 7 3 200 -2.991 16.141 -107us 492us +---- + +the offset of the NMEA source would need to be increased by about 0.504 +seconds. It does not have to be very accurate. As long as the offset of the +NMEA reference clock stays below 0.2 seconds, the PPS reference clock should be +able to determine the seconds corresponding to the pulses and allow the samples +to be used for synchronisation. + == Issues with `chronyc` === I keep getting the error `506 Cannot talk to daemon`