[tz] New Yorker article on David Mills and NTP
Steffen Nurpmeso
steffen at sdaoden.eu
Thu Oct 6 23:24:31 UTC 2022
Garrett Wollman wrote in
<25407.23180.512283.959616 at khavrinen.csail.mit.edu>:
|<<On Thu, 6 Oct 2022 15:35:01 -0700, Guy Harris via tz <tz at iana.org> said:
|> On Oct 6, 2022, at 1:41 PM, Brooks Harris via tz <tz at iana.org> wrote:
|>> I would add that Posix relies on the c standard,
|
|> Which appears neither to mandate nor forbid leap seconds.
...
|The POSIX standard, on the other hand, requires that time_t be an
|integral type, and gives a closed-form formula for how a UTC time is
|to be converted to a time_t which explicitly requires every day to be
|exactly 86,400 seconds long. (POSIX does not include tzcode's
|timegm() interface; applications are expected to copy the formula from
|the standard.) The practical upshot of this is that POSIX systems
|that implement leap seconds must tick the same second twice for a
|positive leap second, and must skip a tick if there is ever a negative
|leap second -- either way, making interval calculations inaccurate if
But only to throw in that for most systems which are not
always-on, and even for some which are, this is rather
hypothetic since hardware clocks that i know drift (and
Linux hwclock(8) documents "The Hardware Clock is usually not
very accurate. However, much of its inaccuracy is completely
predictable - it gains or loses the same amount of time every
day. This is called systematic drift.")
To misuse this drift (it is -2.577933 per ~35 hours here without
/etc/adjtime) to adjust clocks seems quite natural; to me being
able to keep a human clock (civil time) synchronized with the real
day length of our planet remains a cultural achievement, even
extending the according predictive capabilities of Stonehenge or
the Pyramids (in fact many cultures had something similar it
seems).
I agree it is all wrong and when i really focus on the problem
i am always frustrated how bad i code.
CLOCK_TAI would be an alternative for programming purposes, and
having a nice leap second table at hand is a good thing (on the
according ML PH-Kamp came over with a DNS-based solution for leap
announcement a few years back, later stating he was just
reiterating an idea from over a decade earlier: i jumped on this
idea, because i really liked it!)
Unfortunately CLOCK_TAI is not available everywhere.
--steffen
|
|Der Kragenbaer, The moon bear,
|der holt sich munter he cheerfully and one by one
|einen nach dem anderen runter wa.ks himself off
|(By Robert Gernhardt)
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