[ntp:questions] ntpd step recovery time

Nickolay Orekhov nowhere at mail.ru
Mon Apr 23 08:36:48 UTC 2012

2012/4/23 David Woolley <david at ex.djwhome.demon.invalid>

> Nickolay Orekhov wrote:
>> The following sequence of actions performed:
>> 1. The server becomes synchronized
>> 2. Someone wants to measure how much time it will take for ntpd to make a
>> STEP. Using "date" command he changes system time significantly.
>> 3. According to "tinker stepout 60" we assume that after 60 seconds of
>> spike_detect STEP will be performed.
> You need to accumulate at least two minimum delay samples.  The first
> sample enters spike mode and the second one will trigger the step if large
> offset is still present.  When ntpd is operating, smoothly, samples are
> only made every 1024 seconds, although, if I looked more closely, I might
> find that the poll interval is brought down on entering spike state.
> 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.

>> But in reality step will be performed about 5 minutes to perform. Why it
>> takes so long?
> If I remember correctly, ntpd dumps the contents of the 1 of 8 filter and
> waits for the reachability to become acceptable again.
>  Can we guarantee maximum stepout time somehow?
> You should remove the system administrator privileges of the person who
> used the date command on an ntpd controlled machine, instead.  ntpd is not
> specified to handle such behaviour.
> A bigger question is why do you want such a fast response to an event that
> should never happen on a properly configure system, and if it happens
> should be treated with the greatest caution to ensure that really has
> happened?
> 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
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

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