[ntp:hackers] smearing the leap second

Warner Losh imp at bsdimp.com
Fri Jul 10 17:31:15 UTC 2015


> On Jul 10, 2015, at 11:21 AM, Mike S <mikes at flatsurface.com> wrote:
> 
> On 7/10/2015 1:06 PM, Greg Troxel wrote:
>> 
>> The thing I don't really get about the leap second debate is that we
>> have two timescales with the two properties people want.  TAI is
>> straightforward, with no leap seconds, monitic, etc., but not linked to
>> UT1.  UTC has leap seconds but tracks UT1.  So if people don't like UTC,
>> they can just use TAI.   Creating an nth system that's like TAI but with
>> a fixed offset is just more mess, like GPS time.
>> 
>> Of course, if the world's civil authorities decided to rebaseline zone
>> times to TAI, we've have an even bigger jump, once.
> 
> Exactly. It's not UTC which needs fixing, it's called UTC because it's part of the UTx timescales, which are linked to the sky. Removing leap seconds breaks that, with no good alternative. There are already multiple reasonable alternatives available for those who don't want to deal with leap seconds.

If everybody got leap seconds right, then it wouldn’t be such a big issue. Arguing that people that don’t like leap second should use a different time scale is a red herring. People use UTC because it’s promulgated as the thing to use. Yet only a vanishingly small number of systems implement it correctly. The rest deal with the hic-ups the leap second causes as best they can, which is annoying to those than want correctness, but except for some strange kernel bugs from time to time, generally isn’t too severe.

The argument isn’t “I don’t like leap seconds, so let’s throw them away.” The argument is almost nobody gets them right, so why are they in the standard again?

> Trying to fix system problems by redefining UTC to lack leap seconds is like making math easier by redefining Pi to be 3.

That’s a false analogy. UTC is an artificial construct designed for the convenience of humans, while pi is fundamental.

Warner

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