[ntp:questions] NTPD can take 10 hours to achieve stability

unruh unruh at wormhole.physics.ubc.ca
Mon Apr 18 21:09:20 UTC 2011

On 2011-04-18, David J Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> "unruh" <unruh at wormhole.physics.ubc.ca> wrote in message 
> news:slrniqotoj.40a.unruh at wormhole.physics.ubc.ca...
> []
>>> Mine is within about 6 microseconds, in a non-temperature controlled
>>> environment (running 24 x 7).  Looking at the plots it is quite clear 
>>> that
>>> temperature variations are the limiting factor in accuracy, and not 
>>> NTP.
>> No, it is ntpd. It is because ntpd is so slow to respond to errors that
>> and it takes so long to correct for those temp changes, that the
>> accuracy is what it is. (That and ntp's behaviour of throwing away 80%
>> of the data it collects).
> I would be quite willing to test a fast-response option in ntpd to see 
> whether it makes nay difference.
>> IF your file has the correct drift information in it (linux for example
>> with the tsc clock changes its drift about 40PPM on each bootup) and if
>> it has not been very long since the machine was switched off, then yes,
>> it will be accurate very fast. Those are big ifs. The question is how
>> long does it take ntpd to recover from errors. The figures I gave above
>> give you a clue. chrony is at least an order of magnitude faster.
> Well, if Linux is that badly behaved (altering its clock on each boot), I 
> would have said that was an OS defect which needed correction, not 
> altering ntpd to accommodate faulty software!
> For me, performance under normal use is probably more important than 
> performance under error conditions.
> When chrony has a Windows version and provide a similar command-line 
> ability to "ntpq -p" for getting performance data into MRTG I would 
> consider testing it on a client PC here.

Well, I think someone other than the current maintainers will have to
port it to windows. Since windows timekeeping is not the worlds best
anyway, it is probably true that the extra accuracy of chrony is
unnecessary. It does have a command line option "like ntpq -p"
provided by chronyc (depending on what you mean by "like").
 What MRTG is I do not know.

If you are happy with ntpd, by allmeans stay with it.

> Cheers,
> David 

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