[ntp:questions] API for step time server notification

Richard B. Gilbert rgilbert88 at comcast.net
Mon Jul 26 16:33:07 UTC 2010

unruh wrote:
> On 2010-07-26, Thierry MARTIN <thierry-martin at ifrance.com> wrote:
>> On 26 juil, 16:39, unruh <un... at wormhole.physics.ubc.ca> wrote:
>>> On 2010-07-26, Thierry MARTIN <thierry-mar... at ifrance.com> wrote:
>>>> Hello,
>>>> Is there any API that can be used in a program to be "notified" if a
>>>> "step time server" event occurs?
>>>> As far as I could see, it is "only" logged.
>>> You could have something read the logs and notify your program. Or if
>>> you are on Linux/BSD you could run chrony, which does not step.
>>> Mind you if ntpd is stepping after having been running for a few hours,
>>> something is seriously wrong, and needs fixing.
>>>> Thanks in advance for your answers.
>>>> / Thierry
>> Unfortunately, watching the logs does not fit my need.
>> I will try and explain what are my constraints.
>> My program is doing network packet acquisition on several links and
>> needs to sort them - based on the timestamps.
>> Also, many network measurements are very badly affected by time
>> stepping forward or backward.
>> This explains why I'd like to be notified of time steps. (It is easy
>> when time is going backward, but not in the other case).
>> I think ntpd ajusts time by step if the system looses connection to
>> ntp sources for a while (I set up the step threshold to 1s on the ntp
>> server).
> No. ntpd steps if the time is out xby more than 125ms. This is a failure
> of ntpd, but it is NOT something that should happen. 
> Your clocks should not step even if they loose connectivity for a fair
> while if their frequency has been disciplined-- and if  your network
> looses connectivity, then your network monitoring is screwed anyway. 
> You might also want to let the clock freewheel (ie do not use ntp to
> discipline it) but use ntp to find out how far out your clocks actually
> are. Then again you can use that info to correct the times of the
> timestamps after the fact. 
> But this stepping is simply a feature of ntpd. If you do not like it,
> use chrony instead (unless you are on windows). 

Stepping is not exactly a "feature" of NTPD.  It's a last resort for 
fixing a totally screwed up clock.  If your clock is off by fifteen 
minutes, do you *really* want to wait three or four weeks for NTPD to 
fix it "gently"??  There are a few sites that would have no choice but 
to do so but they are extremely careful to avoid the necessity!

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