Leap Second planned for 2016

Sat Jul 9 21:37:36 UTC 2016

POSIX (Unix) (normal) time does not have leap seconds.  
Every POSIX (Unix) (normal) minute has exactly 60 seconds.  
Every POSIX (Unix) (normal) hour has exactly 60 minutes.  
Every POSIX (Unix) (normal) day has exactly 24 hours.
Every POSIX (Unix) (normal) year has 365 days, unless it is a leap year, in which case it has exactly 366 days.

The POSIX time is the number of seconds (or parts thereof) that has passed since midnight, 1 January 1970 GMT.  The time scale is UT1.  Outside of very specialized scientific applications, EVERY computer system everywhere uses POSIX time and does time/date calculations based on POSIX time (UT1).

UTC time has leap seconds.  This is because UTC is a "different" time-scale than the UT1 timescale on which POSIX/Unix time is based.  UTC proceeds at a different "rate" from UT1 and so, from time to time, UTC time must be adjusted to keep it in sync with POSIX/Unix (normal) time.

> -----Original Message-----
> From: NANOG [mailto:nanog-bounces at nanog.org] On Behalf Of
> Valdis.Kletnieks at vt.edu
> Sent: Saturday, 9 July, 2016 15:12
> To: Saku Ytti
> Cc: NANOG list
> Subject: Re: Leap Second planned for 2016
> 
> On Sat, 09 Jul 2016 12:14:03 +0300, Saku Ytti said:
> 
> > Check the implementation on your PC. This is why code is broken and
> > people don't even know it's broken. You have to use monotonic time to
> > measure passage of time, which is not particularly easy to do
> > portable, in some languages.
> 
> It doesn't help that the POSIX standard doesn't represent leap seconds
> anyplace, so any elapsed time calculation that crosses a leap second
> is guaranteed to be wrong....