[ntp:hackers] Leap second list file

Miroslav Lichvar mlichvar at redhat.com
Mon Jan 16 11:30:03 UTC 2012

On Sun, Jan 15, 2012 at 08:14:25PM -0700, Warner Losh wrote:
> >> Except that you don't know how many leap seconds have elapsed.  This makes
> >> running the 'right' time zone impossible. 
> > 
> > I missed a step.  How did we get from leap seconds to time zones?
> right timezone files are a special beast.  You have to know how many
> leap seconds have occurred to get the offset in the kernel to UTC
> corrected properly.

I think the idea was to use the right/UTC timezone just to get the
information when will leap seconds occur, i.e. as a replacement of the
leapsec file. The advantage is that the tzdata package is regularly
updated via system tools, no special action is required from the
admin, ntpd doesn't even have to be restarted.

I'm not sure how useful it's for stratum > 1 clients though. If a
majority of its servers says that leap second is not coming, forcing
the client to execute the leap could only make things worse as it would
step back to the old timescale served by the servers and then back
again once majority of the servers are fixed. Perhaps it would be
useful to extend the source selection algorithm to mark the sources
with wrong leap bit as falsetickers for couple hours/days to give them
time to settle down.

Miroslav Lichvar

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