Hello Alexander, On Tue, May 10, 2011 at 8:17 PM, Alexander Schuch <Alex.Schuch@xxxxxx> wrote: > Hello, > > The NOTES section of time(2) <http://www.kernel.org/doc/man-> > pages/online/pages/man2/time.2.html> says the following: > > "POSIX.1 defines seconds since the Epoch as a value to be > interpreted as the number of seconds between a specified time > and the Epoch, according to a formula for conversion from UTC > equivalent to conversion on the naive basis that leap seconds > are ignored and all years divisible by 4 are leap years." > > I have neither read nor checked the POSIX specification, > but there is an oddity in the statement, because "Years that > are evenly divisible by 100 are not leap years, unless they are > also evenly divisible by 400, in which case they are leap years." - > http://en.wikipedia.org/wiki/Leap_year and cited sources. > > So if POSIX really says that an average year has 365.25 > days, a note should be added to the manual saying that > POSIX differs from the Gregorian calendar. If, however, > an average year has 365.2425 days according to POSIX, > the line in time(2) should be updated to reflect that. Thanks for your report. Your estimation that the man page is odd is of course correct. For man-pages-3.33, I applied the patch below. Cheers, Michael --- a/man2/time.2 +++ b/man2/time.2 @@ -26,7 +26,7 @@ .\" Modified Sat Jul 24 14:13:40 1993 by Rik Faith <faith@xxxxxxxxxx> .\" Additions by Joseph S. Myers <jsm28@xxxxxxxxx>, 970909 .\" -.TH TIME 2 2010-02-25 "Linux" "Linux Programmer's Manual" +.TH TIME 2 2011-09-09 "Linux" "Linux Programmer's Manual" .SH NAME time \- get time in seconds .SH SYNOPSIS @@ -61,16 +61,18 @@ POSIX does not specify any error conditions. .SH NOTES POSIX.1 defines .I seconds since the Epoch -as a value to be interpreted as the number of seconds between a -specified time and the Epoch, according to a formula for conversion -from UTC equivalent to conversion on the naive basis that leap -seconds are ignored and all years divisible by 4 are leap years. +using a formula that approximates the number of seconds between a +specified time and the Epoch. +This formula takes account of the facts that +all years that are evenly divisible by 4 are leap years, +but years that are evenly divisible by 100 are not leap years +unless they are also evenly divisible by 400, +in which case they are leap years. This value is not the same as the actual number of seconds between the time -and the Epoch, because of leap seconds and because clocks are not +and the Epoch, because of leap seconds and because system clocks are not required to be synchronized to a standard reference. -The intention is -that the interpretation of seconds since the Epoch values be -consistent; see POSIX.1 Annex B 2.2.2 for further rationale. +The intention is that the interpretation of seconds since the Epoch values be +consistent; see POSIX.1-2008 Rationale A.4.15 for further rationale. .SH "SEE ALSO" .BR date (1), .BR gettimeofday (2), -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface"; http://man7.org/tlpi/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
