[ntp:questions] Re: What does refer to?

Tim tim at mail.localhost.invalid
Fri Nov 11 14:19:42 UTC 2005


>> script which is run after a PPP connection goes up.  But otherwise you
>> end up with a computer no better than if you *never* had NTP on it.

David Woolley:

> That's not true.  The last available frequency correction is still
> applied. There's no difference in this respect whether or not you have a
> local clock as a local clock never has a time offset so never causes any
> adjustments; all it does is to make it look as though the time is valid,
> so that you continue to serve time other machines.

I can assure that it is.  Consider this:  If I set my clock once, then
hope that it's going to stay correct, it's in the same condition whether I
set that via NTP or some other method (e.g listening to the radio).

Without a running time server, of some description, it's just a clock.
You'd have to be continually verifying time, with something like NTP, to
say you've got a system that could be used as a time server.

For what it's worth, my hardware clock on one motherboard is damn good. 
It's only ever out by about 1 second a month.  I could easily use that as
a local reference clock, if the systems work that way.  But they don't. 
They consider the hardware clock to be unreliable, the software clock to
be correct (despite all the interruptions they get), and use it to keep
diddling the hardware clock.

> If that's not happening, you have a bug, but you will need to install an
> unpatched version, before reporting it here, or you could report it to Red
> Hat.

I wouldn't be surprised.  But before I go about reporting bugs, I think
it's wise to find out what other people know about it.  Which might even
be that they have a solution, already.

> If I remember correctly, if you are using the kernel PLL, this will still
> maintain the frequency correction even after NTP stops in a controlled
> way.  It will always continue to maintain it if NTP crashes.

My experience with NTP stopping wouldn't seem to indicate a crash, just a
dummy spit.  Without at least a local reference, it'd stop serving time if
remote references were lost.  If remote references weren't available when
you tried to start it, it would start then shut down.  Though I think a
certain amount of that was down to the external utilities Red Hat and
Fedora supplied for the user to set the clock / start the server, rather
than NTP itself.

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