[ntp:questions] Slow convergence of NTP with GPS/PPS

Unruh unruh-spam at physics.ubc.ca
Wed Oct 1 06:56:22 UTC 2008

David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:

>Richard B. Gilbert wrote:

>> If you are using a recent version of ntpd, start it with the "-g" 
>> switch.  That will cause it to set the clock to the correct time once 
>> only!  If you have a good drift file, you should be synchronized in 
>> thirty seconds or so and be within ten milliseconds, or less, of the 
>> correct time.

>My understanding was that -g turns off the 1000 second check for the 
>first step, but still leaves the time within +/- 128ms, which will still 
>take an unacceptable time to converge to +/- 5ms.  Certainly the 4.2.4p4 
>documentation makes no claims for it beyond once only disabling the 1000 
>second check.

128ms at 500PPM is 250sec or 4 min. It will take longer than that since the
rate will not peg out, but it should not be hours.
Maybe it is best to set the clock initiallly so that it is out by by more
than 128ms (Eg advance it by 10 sec) and then use -g.

>> Try not to reboot unless absolutely necessary.  I realize that some 
>> versions of Windows need fairly frequent reboots but there are are 

>I imagine this is some sort of embedded system, which he can't control, 
>but might be switched off outside office hours, in part because that is 
>the socially responsible thing to do.

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