[ntp:questions] how to force NTP to use GPS

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Sat Feb 11 23:56:42 UTC 2012

On 02/11/2012 06:11 PM, Richard B. Gilbert wrote:
> On 2/11/2012 4:14 PM, Ron Frazier (NTP) wrote:
>> Hi all,
>> I now have my USB GPS working at an acceptable level on both Windows and
>> Linux using only NTPD. I have the GPS server line set as prefer, but
>> there are other server lines which poll the internet. Sometimes, the
>> system selects an internet clock rather than my GPS. How do I force NTP
>> to use my GPS if it's available, no matter what (within reason). The
>> only time I ever want it to select an internet server is if the GPS
>> fails or is not plugged in.
>> Sincerely,
>> Ron
> ISTR a "prefer" keyword used to instruct NTPD to use a designated
> time source if that source is available. Other sources configured will 
> be used only if the "preferred" source is not available or obviously 
> insane. Or something like that! It goes in NTPD.CONF IIRC.

Hi Richard (and others),

Thanks for the note. I have prefer on my gps line in ntp.conf. I have to 
do more testing. I thought I saw it select another clock anyway some 
time during the day. I know the GPS was available at the time and it 
wasn't insane.

Also, something else strange just happened. I shut down NTPD for 
literally about only a minute to tweak the fudge factor in ntp.conf by 
about 5 ms. When I restarted it, the offset between the computer's clock 
and ALL my time sources including the GPS was about 160 ms. Before the 
shutdown, it was only about 2 ms. I don't think it should drift out 1/6 
sec in one minute. I've restarted NTPD and I'll see what happens.



(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
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Ron Frazier
timekeepingdude AT c3energy.com

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