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by jheitmann 1424 days ago
Why does ntpd lose the smear on a restart? I would have thought that the current smear could be calculated purely based off current non-smear time, plus the config to say when to smear, which is presumably available upon restart.

Also, why were non-linear smears thought to be desirable? Googling just turns up hand-wavy phrases like "easier on clients".
3 comments
hocuspocus 1424 days ago
I came to the comments for the same question about non-linear smearing.

I found more details and motivation in this article: https://developers.redhat.com/blog/2015/06/01/five-different...

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almog 1424 days ago
That was my thought too, pointing out why NTP smearing might be fragile is a crucial point in any argument against leap seconds, and the reasoning in this post are lacking (regardless of the conclusion's correctness).

My only guess is that because smearing takes place at Stratum 2, if the network partitions part of the NTP servers downstream (Stratum 3+), they'll have an offset as large as T/(17 x 3600) (T being the partition duration in seconds). Yet I guess it must be something else for I cannot see why that won't be tolerable.

More generally AFAIK the NTP RFC does not include smearing period, which is why the best practices are to only use smearing in a well controlled environment rather than on public facing NTP networks, but why is this not something that can be fixed? I'm not sure.

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randyrand 1424 days ago
Ya this sounds like bad design.

> current non-smear time

This is the server that keeps that time! ;)

But IMO, the time keeping device should be a separate hardware module with battery backup that is never is restarted.

The computer should not be keeping time to begin with.

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