Re: Bug: Status/Summary of slashdot leap-second crash on new years 2008-2009

Pavel Machek
2009-01-12T16:11:47Z

On Mon 2009-01-05 11:42:35, Linas Vepstas wrote:
> 2009/1/5 <david@lang.hm>:
> > On Mon, 5 Jan 2009, Linas Vepstas wrote:
> >
> >>> Arguably the kernel's responsibility should be to keep track of the
> >>> most fundamental representation of time possible for a machine (that's
> >>> probably TAI) and it is a userspace responsibility to map from that
> >>> value to other time standards including UTC,
> >>
> >> Yes, this really does seem like the right solution.
> >>
> >>> using control files
> >>> which are updated as leap seconds are declared.
> >>
> >> Lets be clear on what "control files" means. This does
> >> *NOT* mean some config file shipped by some distro
> >> for some package. That would be a horrid solution.
> >> People don't install updates, patches, etc. Distros
> >> ship them late, or never, if the distro is old enough.
> >>
> >> A more appropriate solution would be to have
> >> either the kernel or ntpd track the leap seconds
> >> automatically. First, the ntp protocol already provides
> >> the needed notification of a leap second to anyone
> >> who cares about it (i.e. there is no point in getting a
> >> Linux distro involved in this -- a distribution mechanism
> >> already exists, and works *better* than having a distro
> >> do it).
> >
> > I disagree with this. NTP will only know about leap seconds if it was
> > running and connected to a server that advertised the leap seconds during
> > that month.
> >
> > for example, if you installed a new server today, how would it ever know
> > that there was a leap second a couple of days ago?
>
> OK, good point. Unless your distro was less
> than a few days old (unlikely), you are faced with the
> same problem. Sure, eventually, the distro will publish
> an update (which will add to the existing list of 36 leap
> seconds -- which is needed in any case, since no one
> has a server that's been up since 1958), but this is
> unlikely to happen during this install window.
>
> The long term solution would be write an RFC to extend
> NTP to also provide TAI information -- e.g. to add a
> message that indicates the current leap-second offset
> between UTC and TAI.

Offset is not enough; you'd have to provide list of all previous leap
seconds with 'when it happened' timestamps.

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