On Mon, Jan 15, 2024 at 8:15 PM Miroslav Lichvar <mlich...@redhat.com> wrote:
> On Mon, Jan 15, 2024 at 06:57:48PM +0700, James Clark wrote: > > In computing the initial step, how does chrony handle leap seconds? > > > > There are two ways of computing offsets: > > - subtracting the TAI times (so that it is really the number of seconds > > that elapse between the system time and the true time) > > - subtracting the POSIX times (so leap seconds are ignored) > > chronyd corrects the system clock, which ignores leap seconds, so it > expects the second approach. It doesn't do any corrections of the > offset. > This is going to be a bit strange in the vicinity of a positive leap second. Suppose the true time is ahead of the system time by 3 seconds. There are three successive cases around a positive leap second: - the true time is before the start of the leap: in this case the difference in the POSIX system times will be 3 - the true time is after the leap has finished but system time is before the leap: in this case the difference in the POSIX times will be 2 (because 1 second of the difference is a leap second and so ignored) - the system time is after the leap is finished: in this case the difference will again be 3 Are you saying that chrony expects the offset to jump around like this (even though there is no change in the amount by which the clock needs to be corrected)? I can change my code to implement this, if that's what's needed: I would convert both times to POSIX before computing the offset, instead of converting them both to TAI. James
