zdump — timezone dumper
zdump [option...]
[timezone...]
−−versionOutput version information and exit.
−−helpOutput short usage message and exit.
−iOutput a description of time intervals. For each
timezone on the
command line, output an interval-format description of
the timezone. See "INTERVAL FORMAT" below.
−vOutput a verbose description of time intervals. For
each timezone
on the command line, print the time at the lowest
possible time value, the time one day after the lowest
possible time value, the times both one second before
and exactly at each detected time discontinuity, the
time at one day less than the highest possible time
value, and the time at the highest possible time value.
Each line is followed by isdst=D where D is positive, zero, or negative
depending on whether the given time is daylight saving
time, standard time, or an unknown time type,
respectively. Each line is also followed by gmtoff=N if the given local time is known to
be N seconds east of
Greenwich.
−VLike −v, except
omit the times relative to the extreme time values.
This generates output that is easier to compare to that
of implementations with different time
representations.
−c
[loyear,]hiyearCut off interval output at the given year(s). Cutoff
times are computed using the proleptic Gregorian
calendar with year 0 and with Universal Time (UT)
ignoring leap seconds. Cutoffs are at the start of each
year, where the lower-bound timestamp is exclusive and
the upper is inclusive; for example, −c 1970,2070 selects transitions
after 1970-01-01 00:00:00 UTC and on or before
2070-01-01 00:00:00 UTC. The default cutoff is
-500,2500.
−t
[lotime,]hitimeCut off interval output at the given time(s), given
in decimal seconds since 1970-01-01 00:00:00
Coordinated Universal Time (UTC). The timezone determines
whether the count includes leap seconds. As with
−c, the cutoff's
lower bound is exclusive and its upper bound is
inclusive.
The interval format is a compact text representation that is intended to be both human- and machine-readable. It consists of an empty line, then a line "TZ=string" where string is a double-quoted string giving the timezone, a second line "- - interval" describing the time interval before the first transition if any, and zero or more following lines "date time interval", one line for each transition time and following interval. Fields are separated by single tabs.
Dates are in yyyy-mm-dd format and times are in 24-hour hh:mm:ss format where hh<24. Times are in local time immediately after the transition. A time interval description consists of a UT offset in signed ±hhmmss format, a time zone abbreviation, and an isdst flag. An abbreviation that equals the UT offset is omitted; other abbreviations are double-quoted strings unless they consist of one or more alphabetic characters. An isdst flag is omitted for standard time, and otherwise is a decimal integer that is unsigned and positive (typically 1) for daylight saving time and negative for unknown.
In times and in UT offsets with absolute value less than 100 hours, the seconds are omitted if they are zero, and the minutes are also omitted if they are also zero. Positive UT offsets are east of Greenwich. The UT offset -00 denotes a UT placeholder in areas where the actual offset is unspecified; by convention, this occurs when the UT offset is zero and the time zone abbreviation begins with "-" or is "zzz".
In double-quoted strings, escape sequences represent unusual characters. The escape sequences are \s for space, and \", \\, \f, \n, \r, \t, and \v with their usual meaning in the C programming language. E.g., the double-quoted string “"CET\s\"\\"” represents the character sequence CET "\.
Here is an example of the output, with the leading empty line omitted. (This example is shown with tab stops set far enough apart so that the tabbed columns line up.)
TZ="Pacific/Honolulu" - - -103126 LMT 1896-01-13 12:01:26 -1030 HST 1933-04-30 03 -0930 HDT 1 1933-05-21 11 -1030 HST 1942-02-09 03 -0930 HWT 1 1945-08-14 13:30 -0930 HPT 1 1945-09-30 01 -1030 HST 1947-06-08 02:30 -10 HST
Here, local time begins 10 hours, 31 minutes and 26 seconds west of UT, and is a standard time abbreviated LMT. Immediately after the first transition, the date is 1896-01-13 and the time is 12:01:26, and the following time interval is 10.5 hours west of UT, a standard time abbreviated HST. Immediately after the second transition, the date is 1933-04-30 and the time is 03:00:00 and the following time interval is 9.5 hours west of UT, is abbreviated HDT, and is daylight saving time. Immediately after the last transition the date is 1947-06-08 and the time is 02:30:00, and the following time interval is 10 hours west of UT, a standard time abbreviated HST.
Here are excerpts from another example:
TZ="Europe/Astrakhan" - - +031212 LMT 1924-04-30 23:47:48 +03 1930-06-21 01 +04 1981-04-01 01 +05 1 1981-09-30 23 +04 ... 2014-10-26 01 +03 2016-03-27 03 +04
This time zone is east of UT, so its UT offsets are positive. Also, many of its time zone abbreviations are omitted since they duplicate the text of the UT offset.
Time discontinuities are found by sampling the results returned by localtime at twelve-hour intervals. This works in all real-world cases; one can construct artificial time zones for which this fails.
In the −v and
−V output, "UT" denotes the
value returned by gmtime(3), which uses UTC
for modern timestamps and some other UT flavor for timestamps
that predate the introduction of UTC. No attempt is currently
made to have the output use "UTC" for newer and "UT" for
older timestamps, partly because the exact date of the
introduction of UTC is problematic.
This page is part of release 5.11 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
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