ZDUMP(8) System Manager's Manual ZDUMP(8)
NAME
zdump - time zone dumper
SYNOPSIS
zdump [ option ... ] [ zonename ... ]
DESCRIPTION
Zdump prints the current time in each zonename named on the command
line.
These options are available:
--version
Output version information and exit.
-i (This option is experimental: its behavior may change in future
versions.) Output a description of time intervals. For each
zonename on the command line, output an interval-format
description of the zone. See "INTERVAL FORMAT" below.
-v Output a verbose description of time intervals. For each
zonename 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 zonename 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
This format is experimental: it may change in future versions.
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 zone name, 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 time stamps and some other UT flavor for time
stamps that predate the introduction of UTC. No attempt is currently
made to have the output use "UTC" for newer and "UT" for older time
stamps, partly because the exact date of the introduction of UTC is
problematic.
SEE ALSO
newctime(3), tzfile(5), zic(8)
ZDUMP(8)