[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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