| Re: [chrony-users] Can't synchronise: no majority |
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William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ unruh@xxxxxxxxxxxxxx
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On Wed, 25 Mar 2020, Lonnie Abelbeck wrote:
On Mar 25, 2020, at 8:22 AM, Niko Delarich <ndelarich@xxxxxxxxxx> wrote:
Hi,
we use chrony 3.5 in an embedded network device (Linux 4.4.122 armv7l).
In some of our customers installations we've noticed that chrony is sometimes unable to synchronize correctly if the two configured NTP servers don't agree on a time (i.e. the source intervals don't overlap).
Not surprising. How can chrony decide which is the right one, and which source
has gone crazy. That is why it is always advised to use an odd number of
sources. Three allows one to go crazy and for chrony to know it is the one to
ignore. Five allows 2 to go crazy. Of course this also implies that the
sources must be independent. If two of the sources are both tied together in
what they report, (eg both use one third source for their time) then of course
chrony cannot detect that they have both gone crazy. It will assume they are
good and the third one is the bad one. So, use three, not two, independent
sources for time.
...
After comparing the source intervals, the "Can't synchronise: no majority" message is emitted if the two servers don't agree on a time.
...
Or is there maybe a configuration option I'm missing? Setting one of the sources to "trusted" manually is most likely not an option for us since the servers may be assigned by a DHCP server.
I have seen this happen over the years using chrony as well ... adding a third source (or more) is the solution I used.
Lonnie
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