[Ntp] Antw: [EXT] Re: Negative leap‑second?

>>> Daniel Franke <dfoxfranke@gmail.com> schrieb am 03.08.2022 um 01:19 in
Nachricht
<CAJm83bAZgW=xgkO8BAW8HFTsSkGfdQKjkdQnfkyNWRAHdVTB3w@mail.gmail.com>:
> I think predictions of a negative leap second are very premature, but I
> have fewer worries about a negative one than about a positive one. I've
> reviewed quite a lot of leap second handling code and never encountered any
> that gets the positive case right but the negative case wrong; programmers
> clued into the issue at all and generally clued in enough to know that
> negative ones are a possibility. What makes me *less* worried about
> negative leap seconds (rather than just not-much-more worried) is their
> effect on leap-second-naive code: they make POSIX time jump forward rather
> than backward. Lots of code out there wrongly assumes that POSIX time can
> never jump backward. Code that assumes it can never jump forward would get

Well, there are probably also assumptions that CLOCK_MONOTONIC never jumps back (it could when the device is restarted).
It depends how the timestamps are used.

> broken every time someone every time someone suspends their laptop or
> pauses their VM or just puts their OS scheduler under a lot of load.

BTW: Recently I migrated some Linux machines to VMware where the assumption is that the RTC runs on local time (while a standard Linux installation assumes it runs on UTC).
On boot the time was two hours (CEST in effect) ahead and was corrected in a rather brute way (jumping back):
An hour later a "journalctl -S <10 minutes before)" still had an interesting output...

Regards,
Ulrich

> 
> On Tue, Aug 2, 2022, 19:06 Danny Mayer <mayer@pdmconsulting.net> wrote:
> 
>> Apparently the earth's rotation is speeding up:
>> https://www.timeanddate.com/news/astronomy/shortest-day-2022 
>>
>> If we have to subtract a leap-second I think we will see failures, since
>> this is rarely if ever tested.
>>
>> Danny
>>
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