[ntp:questions] NTP 4.2.6p4 Released

David J Taylor david-taylor at blueyonder.co.uk
Wed Sep 28 08:30:30 UTC 2011

> On Wed, Sep 28, 2011 at 05:20 UTC, David J Taylor wrote:
>>> * Added the NTPD_TICKADJ_PPM environment variable for specifying 
>>> baseline
>>>  clock slew on Microsoft Windows
>> Does NTPD_TICKADJ_PPM allow the use of clocks which are more than 500 
>> ppm
>> out?  Sorry if I missed any earlier discussion on this (and I don't run
>> Linux).  How does one go about determining the value to set - just
>> guesswork?
> Yes, it should, just as tickadj and similar capabilities do for POSIX
> systems.  You can determine the value to set any way you like, from
> measurement to guesswork to dart throws.  The adjustment is done at a
> low level in the Windows ntpd port, invisible to the portable ntpd
> code, but is expressed in PPM with the same sign ntpd uses.  If ntpd
> is bouncing up against the +500 PPM limit occasionally, using a
> positive NTPD_TICKADJ_PPM should improve the situation.
>> I'm interested because someone has just reported problems with NTP on a
>> system which gain (or loses) 1 second in 10 minutes!  1 part on 600! 
>> This
>> adjustment could be most helpful.
> It might help, I hope so.  Hopefully the clock rate error is
> consistent enough that after the extreme compensation, it stays well
> under 500 PPM.
> Cheers,
> Dave Hart


That's brilliant!  I didn't know about it, and I don't know how I missed 
it.  Anyway, it's now found, so I've passed on the information and 
recommended this version:


The chap involved is a C programmer on Windows, so he should be able to 
handle it OK.  Of course, if the problem is missed interrupts rather than 
a simple clock-rate issue, it may not help at all.  I had not involved you 
earlier as I feel I've loaded you enough already, and had hoped to solve 
this problem directly.

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Email:  david-taylor at blueyonder.co.uk 

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