1ZDUMP(8) Linux System Administration ZDUMP(8)
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6 zdump - timezone dumper
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9 zdump [ option ... ] [ timezone ... ]
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12 The zdump program prints the current time in each timezone named on the
13 command line.
14
16 --version
17 Output version information and exit.
18 --help Output short usage message and exit.
20 -i Output a description of time intervals. For each timezone on
22 the command line, output an interval-format description of the
23 timezone. See “INTERVAL FORMAT” below.
24 -v Output a verbose description of time intervals. For each time‐
26 zone on the command line, print the time at the lowest possible
27 time value, the time one day after the lowest possible time
28 value, the times both one second before and exactly at each
29 detected time discontinuity, the time at one day less than the
30 highest possible time value, and the time at the highest possi‐
31 ble time value. Each line is followed by isdst=D where D is
32 positive, zero, or negative depending on whether the given time
33 is daylight saving time, standard time, or an unknown time type,
34 respectively. Each line is also followed by gmtoff=N if the
35 given local time is known to be N seconds east of Greenwich.
36 -V Like -v, except omit the times relative to the extreme time val‐
38 ues. This generates output that is easier to compare to that of
39 implementations with different time representations.
40 -c [loyear,]hiyear
42 Cut off interval output at the given year(s). Cutoff times are
43 computed using the proleptic Gregorian calendar with year 0 and
44 with Universal Time (UT) ignoring leap seconds. The lower bound
45 is exclusive and the upper is inclusive; for example, a loyear
46 of 1970 excludes a transition occurring at 1970-01-01 00:00:00
47 UTC but a hiyear of 1970 includes the transition. The default
48 cutoff is -500,2500.
49 -t [lotime,]hitime
51 Cut off interval output at the given time(s), given in decimal
52 seconds since 1970-01-01 00:00:00 Coordinated Universal Time
53 (UTC). The timezone determines whether the count includes leap
54 seconds. As with -c, the cutoff's lower bound is exclusive and
55 its upper bound is inclusive.
56
58 The interval format is a compact text representation that is intended
59 to be both human- and machine-readable. It consists of an empty line,
60 then a line “TZ=string” where string is a double-quoted string giving
61 the timezone, a second line “- - interval” describing the time interval
62 before the first transition if any, and zero or more following lines
63 “date time interval”, one line for each transition time and following
64 interval. Fields are separated by single tabs.
65 Dates are in yyyy-mm-dd format and times are in 24-hour hh:mm:ss format
67 where hh<24. Times are in local time immediately after the transition.
68 A time interval description consists of a UT offset in signed ±hhmmss
69 format, a time zone abbreviation, and an isdst flag. An abbreviation
70 that equals the UT offset is omitted; other abbreviations are double-
71 quoted strings unless they consist of one or more alphabetic charac‐
72 ters. An isdst flag is omitted for standard time, and otherwise is a
73 decimal integer that is unsigned and positive (typically 1) for day‐
74 light saving time and negative for unknown.
75 In times and in UT offsets with absolute value less than 100 hours, the
77 seconds are omitted if they are zero, and the minutes are also omitted
78 if they are also zero. Positive UT offsets are east of Greenwich. The
79 UT offset -00 denotes a UT placeholder in areas where the actual offset
80 is unspecified; by convention, this occurs when the UT offset is zero
81 and the time zone abbreviation begins with “-” or is “zzz”.
82 In double-quoted strings, escape sequences represent unusual charac‐
84 ters. The escape sequences are \s for space, and \", \\, \f, \n, \r,
85 \t, and \v with their usual meaning in the C programming language.
86 E.g., the double-quoted string “"CET\s\"\\"” represents the character
87 sequence “CET "\”.
88 Here is an example of the output, with the leading empty line omitted.
90 (This example is shown with tab stops set far enough apart so that the
91 tabbed columns line up.)
92 TZ="Pacific/Honolulu"
94 - - -10:31:26 LMT
95 1896-01-13 12:01:26 -10:30 HST
96 1933-04-30 03 -09:30 HDT 1
97 1933-05-21 11 -10:30 HST
98 1942-02-09 03 -09:30 HDT 1
99 1945-09-30 01 -10:30 HST
100 1947-06-08 02:30 -10 HST
101 Here, local time begins 10 hours, 31 minutes and 26 seconds west of UT,
103 and is a standard time abbreviated LMT. Immediately after the first
104 transition, the date is 1896-01-13 and the time is 12:01:26, and the
105 following time interval is 10.5 hours west of UT, a standard time
106 abbreviated HST. Immediately after the second transition, the date is
107 1933-04-30 and the time is 03:00:00 and the following time interval is
108 9.5 hours west of UT, is abbreviated HDT, and is daylight saving time.
109 Immediately after the last transition the date is 1947-06-08 and the
110 time is 02:30:00, and the following time interval is 10 hours west of
111 UT, a standard time abbreviated HST.
112 Here are excerpts from another example:
114 TZ="Europe/Astrakhan"
116 - - +03:12:12 LMT
117 1924-04-30 23:47:48 +03
118 1930-06-21 01 +04
119 1981-04-01 01 +05 1
120 1981-09-30 23 +04
121 ...
122 2014-10-26 01 +03
123 2016-03-27 03 +04
124 This time zone is east of UT, so its UT offsets are positive. Also,
126 many of its time zone abbreviations are omitted since they duplicate
127 the text of the UT offset.
128
130 Time discontinuities are found by sampling the results returned by
131 localtime at twelve-hour intervals. This works in all real-world
132 cases; one can construct artificial time zones for which this fails.
133 In the -v and -V output, “UT” denotes the value returned by gmtime(3),
135 which uses UTC for modern timestamps and some other UT flavor for time‐
136 stamps that predate the introduction of UTC. No attempt is currently
137 made to have the output use “UTC” for newer and “UT” for older time‐
138 stamps, partly because the exact date of the introduction of UTC is
139 problematic.
140
142 tzfile(5), zic(8)
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145 This page is part of release 5.04 of the Linux man-pages project. A
146 description of the project, information about reporting bugs, and the
147 latest version of this page, can be found at
148 https://www.kernel.org/doc/man-pages/.
149 2019-03-06 ZDUMP(8)