[tz] Leap seconds puzzle

Paul_Koning at dell.com Paul_Koning at dell.com
Wed Apr 8 19:02:07 UTC 2015


I’ve been sorting to a flurry of questions about leap seconds from colleagues (triggered by the recent announcement of an upcoming leap second).  That sent me to the Theory file, and some experiments.  Those experiments leave me puzzled.

I apologize for going a bit off topic for this list, but the expertise is clearly here.

The Theory file says that POSIX requires leap seconds to be ignored.  And indeed, if I set my system timezone to a POSIX zone description and ask it to convert a time value that’s an integer multiple of 86400, I end up at an exact hour (or half hour) multiple, for example exactly midnight if UTC.  And similarly, if I set my zone to a “right” one and do the conversion, I get a time that’s a few seconds shy of the exact multiple, as expected.

I can also see that my default timezone definitions on my various Unix machines are POSIX ones, again as expected.

So here is the puzzle.  I would expect WWV, and www.time.gov, to reflect leap seconds.  So why would they give me a time that matches, to the second, the POSIX time on my workstation?  Does NTP send POSIX seconds since epoch rather than real ones?  


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