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

David J Taylor david-taylor at blueyonder.co.uk.invalid
Mon Apr 18 17:59:19 UTC 2011

"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.


More information about the questions mailing list