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| -rw-r--r-- | doc/coreutils.texi | 39 |
1 files changed, 38 insertions, 1 deletions
diff --git a/doc/coreutils.texi b/doc/coreutils.texi index 3c7f4e515..751a92078 100644 --- a/doc/coreutils.texi +++ b/doc/coreutils.texi @@ -10493,13 +10493,15 @@ If @var{file} is a symbolic link, the reference timestamp is taken from the target of the symlink, unless @option{-h} was also in effect. @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}] +@cindex leap seconds Use the argument (optional four-digit or two-digit years, months, days, hours, minutes, optional seconds) instead of the current time. If the year is specified with only two digits, then @var{cc} is 20 for years in the range 0 @dots{} 68, and 19 for years in 69 @dots{} 99. If no digits of the year are specified, the argument is interpreted as a date in the current year. -Note that @var{ss} may be @samp{60}, to accommodate leap seconds. +On the atypical systems that support leap seconds, @var{ss} may be +@samp{60}. @end table @@ -14243,11 +14245,13 @@ locale's 12-hour clock time (e.g., @samp{11:11:04 PM}) @cindex epoch, seconds since @cindex seconds since the epoch @cindex beginning of time +@cindex leap seconds seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC@. Leap seconds are not counted unless leap second support is available. @xref{%s-examples}, for examples. This is a @acronym{GNU} extension. @item %S +@cindex leap seconds second (@samp{00}@dots{}@samp{60}). This may be @samp{60} if leap seconds are supported. @item %T @@ -14650,12 +14654,15 @@ See also @ref{Setting the time}. @cindex UTC @cindex Greenwich Mean Time @cindex GMT +@cindex leap seconds @vindex TZ Use Coordinated Universal Time (@acronym{UTC}) by operating as if the @env{TZ} environment variable were set to the string @samp{UTC0}. Coordinated Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for historical reasons. +Typically, systems ignore leap seconds and thus implement an +approximation to UTC rather than true UTC. @end table @@ -14806,6 +14813,36 @@ date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z" 2000-01-01 00:00:00 +0000 @end smallexample +@item +@cindex leap seconds +Typically the seconds count omits leap seconds, but some systems are +exceptions. Because leap seconds are not predictable, the mapping +between the seconds count and a future timestamp is not reliable on +the atypical systems that include leap seconds in their counts. + +Here is how the two kinds of systems handle the leap second at +2012-06-30 23:59:60 UTC: + +@example +# Typical systems ignore leap seconds: +date --date='2012-06-30 23:59:59 +0000' +%s +1341100799 +date --date='2012-06-30 23:59:60 +0000' +%s +date: invalid date '2012-06-30 23:59:60 +0000' +date --date='2012-07-01 00:00:00 +0000' +%s +1341100800 +@end example + +@example +# Atypical systems count leap seconds: +date --date='2012-06-30 23:59:59 +0000' +%s +1341100823 +date --date='2012-06-30 23:59:60 +0000' +%s +1341100824 +date --date='2012-07-01 00:00:00 +0000' +%s +1341100825 +@end example + @end itemize |