NTP and POSIX Time in conflict?

Joe Gwinn joegwinn at mediaone.net
Tue Dec 5 03:47:41 UTC 2000


At 12:12 PM -0500 00/12/4, John Cowan wrote:
>Joe Gwinn wrote:
>  > "Broken-down time" in POSIX resembles UTC, but as leap seconds are
>  > not applied,is not in fact UTC.  The fundamental problem with POSIX
>  > here is that the functions specified for conversion between POSIX
>  > Time and broken-down time fail if leap seconds are involved, in
>  > particular there are time values in one form that cannot be expressed
>  > in the other form.  True UTC, as defined in ITU TR 460-4, does not
>  > share this problem, so posix is broken here.
>The severely practical problem is that clocks on POSIX systems are
>typically set from UTC (either directly, or via NTP) and are then
>expected to tick TAI time units thereafter.  This produces a whole
>set of scales each 1 sec off from its neighbor.

Yes.   Probably won't soon change either.

>Even systems which adjust their local clocks to take leap seconds into
>account typically do so only for a range of leap seconds, roughly,
>those which occurred before the machine was installed.

That is the current issue for sure; what's needed is the schedule of 
past and near future leapseconds.  This cannot be required for POSIX, 
which must support isolated systems, but it should be possibel for 
POSIX systems to use lepasecond information correctly.


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