[ntp:questions] Extracting ntpq like information programmatically

David Woolley david at ex.djwhome.demon.invalid
Fri Mar 29 17:04:43 UTC 2013


Claudio Carbone wrote:

> To do this ideally I should have a single clock, but that is plainly 
> impossible.

Single PPS source with equal length cables to each machine.

> So the next best thing is to use the single machines kernel clocks 
> corrected with the NTP data.
> 
> But to do this I need to periodically save NTP offset and jitter data 
> (delay seems irrelevant).

If delay is irrelevant, jitter is also irrelevant.  In many cases, there 
will be more error in the uncertainty as to whether the delay is mainly 
inbound or outbound, than in the measured jitter.

If the clocks are already synchronised by NTP, none of these will give 
you a better time; all they will do is given you an idea of the error 
bounds of the measurements.  NTP offsets measured at the same time as 
propagation time measurements for other messages will typically have the 
same errors, and should be completely ignored.


> 
> BR
> Claudio



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