[LEAPSECS] internet drafts about zoneinfo (POSIX Time)

[Warner Losh]

> Which special hardware is it that will allow a Unix machine to both 

> tick SI seconds and accurately follow leap seconds?


Any system based on Dave Mill's ntp kernel code will do just this. 
  However, it won't follow the unstated properties of time you may 
assume.  During a leap second, either the last second of the day will 
repeat, or the first second of the next day will repeat.  Time will 
accumulate accuately (with a 1s jump when the leap second happens, since 
POSIX time_t doesn't have a way to encode a leap second that 
distinguishes it from all other seconds).  Applications that care can 
use the ntp_* functions to synthesize a more continuous timescale than 
time_t allows when tracking UTC.  UTC is discontinuous in its time_t 
encoding.  The property of time that is sacraficed to do this is, of 
course, monotonicity.

If you are stratum 1, or slaved to a chain of NTP servers that is 
properly slaved to a stratum 1 that gets leap seconds right, this is 
what will happen if your kernel is based on the kernel ntp code from 
dave mills.

If you are slaved to an NTP server that doesn't get time right, ntpd 
will steer out the error in phase by introducing a small error in 
frequency until the phases are aligned.

If ntp isn't running, then all bets are off.

Warner