Hello An official Google blog post[1] drove me to this question: if the OS implements the kernel discipline, and we have a positive leap second, do we expect that the time will step back one second when the leap second is inserted?
The question arose after mumbling a bit about the blog post. In the post, a Google engineer says that: "Computers traditionally accommodate leap seconds by setting their clock backwards by one second at the very end of the day." By the way, in the NTP FAQ[2] I read: "If the operating system implements the kernel discipline [...] the kernel will handle the leap seconds without further action necessary. If the operating system does not implement the kernel discipline, [...] the situation will be handled just like an unexpected change of time: [...] eventually ntpd will step the time." So I expect that OSs implementing the kernel discipline will go through 23:59:58 -> 23:59:59 -> 23:59:60 -> 00:00:00 in case of a positive leap second, and 23:59:58 -> 00:00:00 -> 00:00:01 in case of a negative one. This shouldn't have any negative effect on applications, unless they are designed to always expect second 00 to follow 59. >From Dr.Mills' pages[3] I understand that the kernel discipline is implemented at least in "Solaris, Tru64, FreeBSD and Linux, and possibly others". Now, I don't know what OSs Google is referring to in that blog post, but I'd expect it is one of those listed above. And they are saying they had to do something because in 2005 their computer clocks stepped back one second and screwed their apps. That's why I think that I am missing something, and hence the question above: are leap seconds supposed to be managed by stepping back the clock when using NTP? Or wasn't it that the OS at the time of the fault didn't support the KD, or had a faulty management of the leap seconds? Or, maybe, it was their apps's fault? Can anyone help me understand? Thanks in advance Ciao -- bronto [1] http://googleblog.blogspot.com/2011/09/time-technology-and-leaping-seconds.html [2] http://www.ntp.org/ntpfaq/NTP-s-algo-real.htm#AEN2499 [3] http://www.eecis.udel.edu/~mills/ntp/html/extern.html _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
