[ntp:questions] Leap second to be introduced in June

Paul tik-tok at bodosom.net
Mon Jan 12 05:44:38 UTC 2015


On Sun, Jan 11, 2015 at 11:34 PM, brian utterback <
brian.utterback at oracle.com> wrote:

>
> On 1/11/2015 10:40 PM, William Unruh wrote:
> > Well, actually as I understand it, ntpd does stop the cclock for that
> > second
>
> That is not the case. That is the behavior that the kernel reference
> code implements which is not part of ntpd.
>

Presumably unruh at invalid read this discription of NTP leapseconds:

There are three approaches to implementing a leap second. The first
> approach is to increment the system clock during the leap second and
> continue incrementing following the leap. The problem with this approach is
> that conversion to UTC requires knowledge of all past leap seconds and
> epoch of insertion. The second approach is to increment the system clock
> during the leap second and step the clock backward one second at the end of
> the leap second. This is the approach taken by the POSIX conventions. The
> problem with this approach is that the resulting timescale is discontinuous
> and ambiguous, since a reading during the leap is repeated one second
> later. The third approach is to *freeze* the clock during the leap second
> allowing the time to catch up at the end of the leap second. This is the
> approach taken by the NTP conventions.
>
 And further

> If the precision time kernel modifications have been implemented, the
> kernel includes a state machine that implements the actions required by the
> scenario. The state machine implemented in most recent Unix kernels is
> described in the nanokernel
> <sftp://www.eecis.udel.edu/%7Emills/nanokernel.tar.gz> software
> distribution. At the first occurrence of second 3,124,137,600, the system
> clock is stepped backward one second. The operating system kernel time
> conversion routines can recognize this condition and show the leap second
> as number 60.
>
The table presented on that page notes that the NTP timestamps for :60 (the
leap second) and :00 are the same.  Of course things could have changed
since 12-May-2012 23:43 UTC when that page was last revised.

Strictly speaking the answer to the OP is "it depends".  Not only on the
system but how you ask the implicit question -- what time is it.


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