Tony Finch wrote: > The IERS Bulletins C state a value of UTC-TAI "until further notice".
As I understand this, it just means that yet it's not known if and when another leap second will have to be scheduled. > However the machine-readable files from IERS and NIST give an expiry date > of a few days less than 6 months after the announced (lack of) leap > second, or a bit more than 11 months after the latest Bulletin C. > Is this expiry date reliable or just advisory? History suggests it's > reliable, but the standards do not. In my opinion this expiration date is very important for those who evaluate the file, e.g. ntpd. If ntpd had a leap second file which doesn't contain a leap second after 2016, it didn't know it there really was no other leap second, or if only the file was too old and hadn't been updated. In the latter case ntpd wouldn't even know if the TAI/UTC offset derived from the available leap second file is still valid, or if another leap second has been inserted in the mean time, and the TAI/UTC offset has changed. With the expiration date ntpd can be sure there was no other leap second, and the TAI/UTC offset is still valid, as long as the current time is before the expiration date, and the file can be ignored after it has expired. If the bulletin C is published once every 6 months, and you have the bulletin from January, you know for sure if there will be a leap second at the end of June, or not. However, only the next bulletin C from next July will tell you if there will be leap second at the end of December. So in January you can be sure the information you have won't change until shortly before the end of December, which is about 11 months. Even after the next bulletin C and leap second file have been published in July, things won't change at least up to the expiration date of the previous file. So you have still about 5 months to deploy the leap second file from July to your ntpd instances, before anything expire. One way to propagate a new leap second file is to - add the new file to the TZ DB some time after tit has been published - the new file appears in the TZ DB when a new TZ DB versio is released - after this it appears at the IANA web page, and eventually in software update packages for your favorite operating system In summary, it can take weeks or even months until the file is available everywhere. So IMO it's very practical that the expiration date is there, and that you have about 5 months to deploy a new version. Martin -- Martin Burnicki Senior Software Engineer MEINBERG Funkuhren GmbH & Co. KG Email: [email protected] Phone: +49 5281 9309-414 Linkedin: https://www.linkedin.com/in/martinburnicki/ Lange Wand 9, 31812 Bad Pyrmont, Germany Amtsgericht Hannover 17HRA 100322 Geschäftsführer/Managing Directors: Günter Meinberg, Werner Meinberg, Andre Hartmann, Heiko Gerstung Websites: https://www.meinberg.de https://www.meinbergglobal.com Training: https://www.meinberg.academy _______________________________________________ LEAPSECS mailing list [email protected] https://pairlist6.pair.net/mailman/listinfo/leapsecs
