ZDUMP(8) (2020-04-27) ZDUMP(8)
NAME
zdump - timezone dumper
SYNOPSIS
zdump [ option ... ] [ timezone ... ]
DESCRIPTION
ds - - 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 lqINTERVAL FORMATrq
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 sec-
ond before and exactly at each detected time disconti-
nuity, the time at one day less than the highest possi-
ble 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 calen-
dar 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.
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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 con-
sists of an empty line, then a line lqTZ=stringrq where string
is a double-quoted string giving the timezone, a second line
lq intervalrq describing the time interval before the first
transition if any, and zero or more following lines lqdate
time intervalrq, one line for each transition time and fol-
lowing 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 immedi-
ately 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 stan-
dard 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 unspeci-
fied; by convention, this occurs when the UT offset is zero
and the time zone abbreviation begins with lqrq or is lqzzzrq.
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
lq"CET\s\"\\"rq represents the character sequence lqCET "\rq.
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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. Immedi-
ately 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 posi-
tive. 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, lqUTrq denotes the value returned by
gmtime(3), which uses UTC for modern timestamps and some
other UT flavor for timestamps that predate the introduction
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of UTC. No attempt is currently made to have the output use
lqUTCrq for newer and lqUTrq for older timestamps, partly
because the exact date of the introduction of UTC is prob-
lematic.
SEE ALSO
tzfile(5), zic(8)
COLOPHON
This page is part of release 5.10 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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