[ntp:questions] Writing the drift file

Magnus Danielson magnus at rubidium.dyndns.org
Sat Mar 7 11:50:59 UTC 2015


Harlan,

On 03/07/2015 12:12 PM, Harlan Stenn wrote:
> OK, a fair amount of good stuff is being discussed.
>
> Do we mostly all agree that the purpose of the drift file is to give
> ntpd a hint as to the frequency drift at startup?
>
> If so...
>
> The current mechanism is designed to handle the case where ntpd is
> restarted fairly quickly, so there's a good chance the same drift value
> will work.

Remember that for embedded devices, the operational conditions may be 
such that it's not a "quick restart" at all times. You cannot assume and 
know when it will go up the next time after being powered off. It can be 
minutes, hours, weeks, years.

Just like the leap-second file, the time of the drift-file is relevant, 
and if it is "too old", it is one (of several) reasons to disqualify it.

Relying on the time-stamp of the file can be trouble-some, as it may not 
be respected by file-management. Writing it into the file is more robust.

Cheers,
Magnus


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