Leap Second support in computers

Abstract

The seconds-in-epoch method of representing current time in computers presents problems when required to (a) represent UTC, (b) be monotonic and (c) have sub-second accuracy, as these are contradictory requirements in the presence of Leap Seconds. We analyze various proposed solutions to this conundrum, for both operating systems and NTP. (What good is microsecond-level clock synchronization if the clock can be off by a full second?) We then propose a general solution: TAI-based system time, with conversion to UTC by comparing to a TAI-based threshold and then subtracting the appropriate Leap Second Offset.