[ntp:questions] prefer in ntp.conf

Jason Rabel jason at extremeoverclocking.com
Wed Jun 13 19:25:29 UTC 2007


What GPS are you using? What OS? What does your ntpq -p data look like? 

If you get a receiver with TRAIM, then you can have it disable the PPS
output when it detects itself getting out of sync, either by bad data or no
lock. Otherwise most GPSes will just keep pulsing away none-the-wiser
(except for their NMEA data which NTP doesn't check against).

You *could* write extra code in the driver to check various NMEA sentences
(which why it hasn't been done I'm not sure) to make sure it has a proper

Or as someone else mentioned, ensure that your antenna has a proper view of
the sky so you do not loose lock.

I wrote a post just a day or two ago about the PREFER source and how if you
have several internet sources they can out weigh your local (more accurate)
source and thus discard it if you do not have the PREFER flag set. So it can
be a potential issue.


>I am using a GPS nmea/pps source (lets not go into the heart-ache
>involved in getting that working), and a very recent download of ntp
>source, with the nmea patch. Obviously I have a few internet sources as
>well, but use the prefer keyword for the pps source. Obviously when it
>is working the pps is about as accurate as I can get. However when I run
>ntpq -p it isn't quite doing as I want.
>I want to lock exactly to that pps source WHILE IT IS SENSIBLE, and to
>drop back to the internet when it has lost satellites. However ntp
>appears to be taking an average, loaded towards the GPS source. When the
>GPS looses satellites and goes beserk ntp sensibly drops it as a source.
>Your suggestions would be welcomed.

More information about the questions mailing list