NTP and POSIX Time in conflict?
jcowan at reutershealth.com
Mon Dec 4 17:12:57 UTC 2000
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.
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.
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