[ntp:questions] NTP not syncing

Charles Elliott elliott.ch at verizon.net
Fri Dec 6 10:27:30 UTC 2013

You might be able to do better.  In QC an average of a randomly gathered 
sample of a continuous variable is distributed as normal (Gaussian).
If NTPD kept a few more statistics (state), it could measure the freq
and determine if it is outside of 3 standard deviations of the grand
mean of past observations of freq.  If it is outside then gather several
more observations of freq (5 total would be best, but 2 or three might
do) and compute the average.  If that average is outside 3 stdDev of 
the mean, then the probability of that result is so low (< 0.05) that
it could not have happened by chance; something has changed.  NTPD must
use the new average as the current freq and include it in the grand mean,
but the user should be warned that something is awry.  On the other hand,
if the 2 or 3 new observations of the freq are not close to the original,
then just throw away the latter.

Charles Elliott

-----Original Message-----
From: questions-bounces+elliott.ch=verizon.net at lists.ntp.org
[mailto:questions-bounces+elliott.ch=verizon.net at lists.ntp.org] On Behalf Of
Sent: Friday, December 6, 2013 3:47 AM
To: questions at lists.ntp.org
Subject: Re: [ntp:questions] NTP not syncing

On 2013-12-06, David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> On 04/12/2013 21:25, Terje Mathisen wrote:
> []
>> It is very common, IF you are running on Linux!
>> The base frequency is recalculated each time you restart, which means 
>> that steps of 100-200 ppm from one reboot to the next can be expected.
>> Terje
> I'm surprised to hear of this problem, as I've not been aware of it in 
> years of running FreeBSD systems, and in more than a year of running
> (now) five Raspberry Pi Linux systems.  Perhaps I've been lucky?  As 
> they are mainly experimental PCs, the RPi cards are rebooted more than

As I said, I think that in the more recent kernels Linux has fixed this.
Since the RPi is only about 2 years old, its linux is a recent kernel. 

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