focal (8) zdump.8.gz
NAME
zdump - timezone dumper
SYNOPSIS
zdump [ option ... ] [ timezone ... ]
DESCRIPTION
The zdump program prints the current time in each timezone named on the command line.
OPTIONS
--version
Output version information and exit.
--help Output short usage message and exit.
-i Output a description of time intervals. For each timezone on the command line, output an
interval-format description of the timezone. See “INTERVAL FORMAT” below.
-v Output 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.
-V Like -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,]hiyear
Cut 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. The lower
bound is exclusive and the upper is inclusive; for example, a loyear of 1970 excludes a transition
occurring at 1970-01-01 00:00:00 UTC but a hiyear of 1970 includes the transition. The default
cutoff is -500,2500.
-t [lotime,]hitime
Cut 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.
INTERVAL FORMAT
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"
- - -10:31:26 LMT
1896-01-13 12:01:26 -10:30 HST
1933-04-30 03 -09:30 HDT 1
1933-05-21 11 -10:30 HST
1942-02-09 03 -09:30 HDT 1
1945-09-30 01 -10:30 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"
- - +03:12:12 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.
LIMITATIONS
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.
SEE ALSO
tzfile(5), zic(8)
COLOPHON
This page is part of release 5.05 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/.
2019-03-06 ZDUMP(8)