[ntp:questions] Ignore one server except in extreme conditions?

A C agcarver+ntp at acarver.net
Wed Nov 16 07:47:32 UTC 2011

On 11/15/2011 23:28, Harlan Stenn wrote:
> OK, and you understand that the NMEA sentence is expected to be correct
> to only +/- 0.5sec, as the PPS signal is un-numbered and the purpose of
> the NMEA data is to identify the time at the pulse of the PPS signal.

Yes, the PPS is unnumbered however if I have valid and reachable 
Internet server then I have numbers from them, too. PPS is only serving 
as the clock tick, I understand that fully.  But you're missing the 
point of my question:

I don't care about the exact accuracy of the NMEA.  I mention the NMEA 
to point out that it is unstable and I would like it to not be part of 
the timing computations unless no other server is available.  That's 
what I'm asking.  If I use the "noselect" option, it is never a valid 
time server no matter what.  If I use "prefer", it's always a valid time 
server.  I'm asking if there's a way to configure ntpd such that 
everything EXCEPT NMEA is a preferred peer unless all the other peers 
are dead in which case fall back to NMEA (all predicated on the GPS 
being functional, if not that's a completely different issue).

Right now, it is almost always part of the valid group of servers.  It 
is never marked as a false ticker or an outlier even if its data is 
terrible compared to any of the other five configured Internet servers.

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