[ntp:questions] ntpd step recovery time

David Woolley david at ex.djwhome.demon.invalid
Mon Apr 23 20:54:12 UTC 2012


Nickolay Orekhov wrote:

>> Sorry, I can't understand this passage. 1024 seconds ~17 minutes. So
> according to this STEP will occur in 17 minutes minimum and 17*2 minutes
> maximum? But as I see it takes approximately 4-5 minutes.
> 

ntpd cannot even do the first steps in preparing for a step until it has 
had a poll response that indicates there is a problem with the time. 
With a default configuration and good servers (no reference clocks) ntpd 
will only poll each server approximately every 2**10 seconds.  If you 
have multiple servers, there is a good chance that one will come up 
before then.  If you have reference clocks, the poll interval may have 
been clamped by them.  If you have poor quality time servers or a poor 
quality system clock, the poll interval may not get to maxpoll.  If you 
have not let the system run long enough before trying to break it, it 
may not have reached maxpoll.

Although I could go to the code and try and work out when the next step 
in the process happens, it would be a waste of my time as you appear to 
be abusing ntpd by imposing a requirement that it was never designed to 
meet, exact on a best effort basis, as a last resort.

>>
>> Well, yes. I understand this. We are going to pass some exams with our
> system and there's a parameter we need to mention. And I have to say, for
> example: "reaction to the STEP will be 5 minutes max". To do it i have to

Then get the specification corrected.  It should actually be specifying 
that the upstream server should maintain sufficient accuracy that steps 
should never happen, and that there should be management procedures to 
prevent people trying to manually set the time.

> understand how this STEP works. I expect maximum reaction time in 1 minute
> or so accoding to configuration but i still can't understand why it is much
> longer.

You are trying to something as a normal operation that is actually a 
last resort error recovery strategy.  The specification writer doesn't 
understand the purpose of ntpd.



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