[LEAPSECS] LEAPSECS Digest, Vol 45, Issue 1

Zefram zefram at fysh.org
Fri Sep 3 12:02:48 EDT 2010

Ian Batten wrote:

>I have a dim memory, based on wrestling with one of the *BSD's NTP

>implementation in the mid 1990s, that one Unix decided to tick TAI

>rather than UTC and move leap-seconds into userspace. But it's all very


The Olson timezone database has some support for this. It has a listing
of leap seconds, which can be included into tzfiles. The zoneinfo-right
directory has this version of the tzfiles, whereas the zoneinfo-posix
directory has tzfiles that do not mention leap seconds.

A wrinkle is the divergence of TAI and UTC prior to 1972, which cannot
be properly modelled using leap seconds. I understand that, as a
result, the time_t in these systems actually depicts TAI-10s, not TAI.
These time_t values coincide with the UTC-based POSIX time_t values for
the first half of 1972, and in 2010 the two time_t values differ by 24.
I've never seen such a system in operation, though, so I can't confirm
that it works this way.


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