[ntp:questions] Win7: ntpd adjusting time backwards

unruh unruh at invalid.ca
Mon Dec 10 21:54:17 UTC 2012

On 2012-12-10, Jeroen Mostert <jmostert at xs4all.nl> wrote:
> On 2012-12-10 22:18, David Woolley wrote:
>> Jeroen Mostert wrote:
>>> For what it's worth, after all of that, the offset is steadily zigzagging
>>> between 27 and 41 ms, which I'm guessing is about the best you can hope for on
>>> a Windows machine with Internet sync. There have not been any major time step
>>> adjustments.
>> Offsets should be scattered around zero. If they are all the same sign,
>> something is wrong.
> OK. Well, that's too bad, I guess.
> Throw me a bone here, fellas. It's nice to know something is wrong, but if all I 
> can see is that all peers consistently report offsets in this range, the best I 
> can conclude is that either ntpd simply isn't successful in disciplining the 
> clock appropriately, or there is some network problem going on that someone who 
> understands the NTP protocol could probably diagnose. That someone would not yet 
> be me.
> If I offset the offsets (pardon my math) by -33 milliseconds, I'd roughly have a 
> zero axis that they'd be swinging around with a range of -10/+10. According to 
> unruh, even that would still be horrible in terms of accuracy, so I'm not sure 
> if that's fair in its simplicity.
Ah, if it really is 33 ms off on average, then yes something is wrong.
I assumed that you meant that the width of the scatter was 27-41ms, not
that the actual offset was always one sign and that far off. 

However I do have to ask what this offset is.
What are your server entries in ntp.conf? Is this offset the offset from
the same server that is being used to set the time? Maybe a few lines
from /var/log/ntp/peerstats.xxxxxxx would let us see what the offset was
doing. Or using some of the plotting programs to plot the offsets
measured from the varios servers.

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