1 .\" %%%LICENSE_START(PUBLIC_DOMAIN)
2 .\" This page is in the public domain
5 .TH ZDUMP 8 2020-04-27 "" "Linux System Administration"
7 zdump \- timezone dumper
16 .ie '\(lq'' .ds lq \&"\"
18 .ie '\(rq'' .ds rq \&"\"
21 \\$3\*(lq\\$1\*(rq\\$2
23 .ie \n(.g .ds - \f(CW-\fP
27 program prints the current time in each
29 named on the command line.
33 Output version information and exit.
36 Output short usage message and exit.
39 Output a description of time intervals. For each
41 on the command line, output an interval-format description of the
47 Output a verbose description of time intervals.
51 print the time at the lowest possible time value,
52 the time one day after the lowest possible time value,
53 the times both one second before and exactly at
54 each detected time discontinuity,
55 the time at one day less than the highest possible time value,
56 and the time at the highest possible time value.
57 Each line is followed by
61 is positive, zero, or negative depending on whether
62 the given time is daylight saving time, standard time,
63 or an unknown time type, respectively.
64 Each line is also followed by
66 if the given local time is known to be
68 seconds east of Greenwich.
73 except omit the times relative to the extreme time values.
74 This generates output that is easier to compare to that of
75 implementations with different time representations.
77 .BI "\*-c " \fR[\fIloyear , \fR]\fIhiyear
78 Cut off interval output at the given year(s).
79 Cutoff times are computed using the proleptic Gregorian calendar with year 0
80 and with Universal Time (UT) ignoring leap seconds.
81 Cutoffs are at the start of each year, where the lower-bound
82 timestamp is exclusive and the upper is inclusive; for example,
84 selects transitions after 1970-01-01 00:00:00 UTC
85 and on or before 2070-01-01 00:00:00 UTC.
89 .BI "\*-t " \fR[\fIlotime , \fR]\fIhitime
90 Cut off interval output at the given time(s),
91 given in decimal seconds since 1970-01-01 00:00:00
92 Coordinated Universal Time (UTC).
95 determines whether the count includes leap seconds.
98 the cutoff's lower bound is exclusive and its upper bound is inclusive.
100 The interval format is a compact text representation that is intended
101 to be both human- and machine-readable. It consists of an empty line,
106 is a double-quoted string giving the timezone, a second line
107 .q "\*- \*- \fIinterval\fP"
108 describing the time interval before the first transition if any, and
109 zero or more following lines
110 .q "\fIdate time interval\fP",
111 one line for each transition time and following interval. Fields are
112 separated by single tabs.
116 format and times are in 24-hour
120 Times are in local time immediately after the transition. A
121 time interval description consists of a UT offset in signed
123 format, a time zone abbreviation, and an isdst flag. An abbreviation
124 that equals the UT offset is omitted; other abbreviations are
125 double-quoted strings unless they consist of one or more alphabetic
126 characters. An isdst flag is omitted for standard time, and otherwise
127 is a decimal integer that is unsigned and positive (typically 1) for
128 daylight saving time and negative for unknown.
130 In times and in UT offsets with absolute value less than 100 hours,
131 the seconds are omitted if they are zero, and
132 the minutes are also omitted if they are also zero. Positive UT
133 offsets are east of Greenwich. The UT offset \*-00 denotes a UT
134 placeholder in areas where the actual offset is unspecified; by
135 convention, this occurs when the UT offset is zero and the time zone
136 abbreviation begins with
141 In double-quoted strings, escape sequences represent unusual
142 characters. The escape sequences are \es for space, and \e", \e\e,
143 \ef, \en, \er, \et, and \ev with their usual meaning in the C
144 programming language. E.g., the double-quoted string
145 \*(lq"CET\es\e"\e\e"\*(rq represents the character sequence \*(lqCET
149 Here is an example of the output, with the leading empty line omitted.
150 (This example is shown with tab stops set far enough apart so that the
151 tabbed columns line up.)
157 .nr w \w'1896-01-13 'u+\n(.i
158 .ta \w'1896-01-13 'u +\w'12:01:26 'u +\w'-103126 'u +\w'HWT 'u
159 TZ="Pacific/Honolulu"
161 1896-01-13 12:01:26 -1030 HST
162 1933-04-30 03 -0930 HDT 1
163 1933-05-21 11 -1030 HST
164 1942-02-09 03 -0930 HWT 1
165 1945-08-14 13:30 -0930 HPT 1
166 1945-09-30 01 -1030 HST
167 1947-06-08 02:30 -10 HST
172 Here, local time begins 10 hours, 31 minutes and 26 seconds west of
173 UT, and is a standard time abbreviated LMT. Immediately after the
174 first transition, the date is 1896-01-13 and the time is 12:01:26, and
175 the following time interval is 10.5 hours west of UT, a standard time
176 abbreviated HST. Immediately after the second transition, the date is
177 1933-04-30 and the time is 03:00:00 and the following time interval is
178 9.5 hours west of UT, is abbreviated HDT, and is daylight saving time.
179 Immediately after the last transition the date is 1947-06-08 and the
180 time is 02:30:00, and the following time interval is 10 hours west of
181 UT, a standard time abbreviated HST.
184 Here are excerpts from another example:
190 TZ="Europe/Astrakhan"
192 1924-04-30 23:47:48 +03
203 This time zone is east of UT, so its UT offsets are positive. Also,
204 many of its time zone abbreviations are omitted since they duplicate
205 the text of the UT offset.
207 Time discontinuities are found by sampling the results returned by localtime
208 at twelve-hour intervals.
209 This works in all real-world cases;
210 one can construct artificial time zones for which this fails.
218 denotes the value returned by
220 which uses UTC for modern timestamps and some other UT flavor for
221 timestamps that predate the introduction of UTC.
222 No attempt is currently made to have the output use
226 for older timestamps, partly because the exact date of the
227 introduction of UTC is problematic.
231 .\" This file is in the public domain, so clarified as of
232 .\" 2009-05-17 by Arthur David Olson.