[ntp:questions] Lep seconds

David L. Mills mills at udel.edu
Fri Jan 4 15:03:03 UTC 2008


Details on how leapseconds are handled are in the NTP leapseconds 
executive summary on the NTP Project Page linked from www.ntp.org. The 
return code from ntp-gettime() reveals when a leap second is or is not 
in progress. In the intended model, ctime or equivalant should notice 
this an map 0 to 60 for the second second. At the end of this second the 
ASCII seconds number will resume from 0. So far as I know, nobody has 
ever implemented that.


Mark Newman wrote:

> Unruh - thanks for responding.  You are the only one
> who did.  
> I certainly did not mean to disparage NTP time.  I
> have spec'ed that it be used on our system.  Where I
> run into problems is when a leap second occurs. 
> According to everything I've read when  NTP signals
> the operating system that the second is occurring it
> also outputs time.  It uses the POSIX standard method
> - duplicate a second (or in some cases stretch the
> last second).  This causes confusion when a time
> sample is taken before the leap second and one during
> the leap second.  The UTC standard (which only
> addresses ascii time representations) actually counts
> the second 0..60 rather than 0..59.
> At this point I am obligated to use UTC and NTP.
> Tht missing second is causing me to get a lot of heat.
>  Does anyone know of a way to get NTP to count the
> leap second rather than to delete it?  Or am I missing
> the point.
>>I don't want to step on anyones toes but I am getting
>>a lot of heat over using a POSIX compliant ntp re
> leap
>>seconds.  The 1 second error inserted can cause a lot
>>of trouble.
> Exactly what heat are you getting and what trouble is
> it causing you?
> Perhaps if you tell us the problem rather than your
> solution, we could come
> up with a solution.
>>I now that the Olsen mod changes most Unix/Linux time
>>processing to handle the leap second in a
>>theoretically correct manner rather than being POSIX
> I have no idea what "a theoretically correct manner "
> is. The Posix IS a
> theoretically correct manner. 
>>compliant.  Is there a similar mod for NTP.  I am
>>hoping that there is a mod that will cause NTP to
>>supply theoretical UTC (even if it is not ascci).
> NTP DOES supply both theoretical and practical UTC. 
> I think what you are worried about is that you want
> your system to provide
> something like TIA-- Atomic time-- which has no leap
> seconds. I believe the
> Olsen mods have your system clock run on atomic time
> and then use the
> leapsecond file and the zoneinfo file for your region
> to translate that to
> your local time.
> You could just set up ntp to add 33 sec to its time,
> and you would have
> atomic time.
>>                           Mark

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