[ntp:questions] Number of Stratum 1 & Stratum 2 Peers

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Wed Dec 17 14:45:20 UTC 2014


On 2014-12-16 10:28, Phil W Lee wrote:
> Martin Burnicki <martin.burnicki at meinberg.de> considered Tue, 16 Dec
> 2014 12:48:57 +0100 the perfect time to write:
>
>> Brian Inglis wrote:
>>> It would be interesting to know what percentage of the pool servers even
>>> use  a leapseconds file, and how many of those have a valid copy.
>>> I am certain that very few clients use a leapseconds file.
>>>
>>> OTOH the timezone/zoneinfo package uses its own leapseconds file (for  "right"
>>> time - now zoneinfo-leaps), and distributes that and the original, a script
>>> that checks and converts it to their own format, and utilities that use it.
>>
>> As far as I can see the the leap second file shipped with the tzdata
>> package is generated automatically from a leap second file in NIST format.
>>
>> However, there is an important limitation: the tzdata version of the
>> leap second file is missing an expiration date, so even if a program
>> like ntpd could use this file directly it would never know if no more
>> leap second has been scheduled after the last one mentioned in this
>> file, or if the file just hasn't been updated recently enough.
>
> If it compared the file it has with the one available from tzdata, it
> could see if there was a difference - it's not exactly huge.
> Even better would be if a checksum or version number was available as
> well, so that could just be compared to the current one, and a new one
> only downloaded if required.

The HTTP modified header does that well if provided by the web server
for a file - it is for most files on most web servers, also for FTP files.
All my network update scripts use wget -N to timestamp files and check
the modified header to see if an update needs downloaded.
Update scripts can then check to see if a file timestamp, and internal
expiry date, release date, or version number has changed, and checksums
are correct, to decide whether to apply the update, or if it can be skipped.

-- 
Take care. Thanks, Brian Inglis


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