mirror of https://github.com/mkerrisk/man-pages
233 lines
6.8 KiB
Groff
233 lines
6.8 KiB
Groff
.\" %%%LICENSE_START(PUBLIC_DOMAIN)
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.\" This page is in the public domain
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.\" %%%LICENSE_END
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.\"
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.TH ZDUMP 8 2020-04-27 "" "Linux System Administration"
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.SH NAME
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zdump \- timezone dumper
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.SH SYNOPSIS
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.B zdump
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[
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.I option
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\&... ] [
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.I timezone
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\&... ]
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.SH DESCRIPTION
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.ie '\(lq'' .ds lq \&"\"
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.el .ds lq \(lq\"
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.ie '\(rq'' .ds rq \&"\"
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.el .ds rq \(rq\"
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.de q
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\\$3\*(lq\\$1\*(rq\\$2
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..
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.ie \n(.g .ds - \f(CW-\fP
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.el ds - \-
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The
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.B zdump
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program prints the current time in each
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.I timezone
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named on the command line.
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.SH OPTIONS
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.TP
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.B \*-\*-version
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Output version information and exit.
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.TP
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.B \*-\*-help
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Output short usage message and exit.
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.TP
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.B \*-i
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Output a description of time intervals. For each
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.I timezone
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on the command line, output an interval-format description of the
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timezone. See
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.q "INTERVAL FORMAT"
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below.
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.TP
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.B \*-v
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Output a verbose description of time intervals.
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For each
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.I timezone
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on the command line,
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print the time at the lowest possible time value,
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the time one day after the lowest possible time value,
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the times both one second before and exactly at
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each detected time discontinuity,
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the time at one day less than the highest possible time value,
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and the time at the highest possible time value.
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Each line is followed by
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.BI isdst= D
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where
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.I D
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is positive, zero, or negative depending on whether
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the given time is daylight saving time, standard time,
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or an unknown time type, respectively.
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Each line is also followed by
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.BI gmtoff= N
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if the given local time is known to be
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.I N
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seconds east of Greenwich.
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.TP
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.B \*-V
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Like
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.BR \*-v ,
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except omit the times relative to the extreme time values.
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This generates output that is easier to compare to that of
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implementations with different time representations.
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.TP
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.BI "\*-c " \fR[\fIloyear , \fR]\fIhiyear
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Cut off interval output at the given year(s).
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Cutoff times are computed using the proleptic Gregorian calendar with year 0
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and with Universal Time (UT) ignoring leap seconds.
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Cutoffs are at the start of each year, where the lower-bound
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timestamp is exclusive and the upper is inclusive; for example,
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.B "\*-c 1970,2070"
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selects transitions after 1970-01-01 00:00:00 UTC
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and on or before 2070-01-01 00:00:00 UTC.
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The default cutoff is
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.BR \*-500,2500 .
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.TP
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.BI "\*-t " \fR[\fIlotime , \fR]\fIhitime
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Cut off interval output at the given time(s),
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given in decimal seconds since 1970-01-01 00:00:00
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Coordinated Universal Time (UTC).
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The
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.I timezone
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determines whether the count includes leap seconds.
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As with
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.BR \*-c ,
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the cutoff's lower bound is exclusive and its upper bound is inclusive.
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.SH "INTERVAL FORMAT"
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The interval format is a compact text representation that is intended
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to be both human- and machine-readable. It consists of an empty line,
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then a line
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.q "TZ=\fIstring\fP"
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where
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.I string
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is a double-quoted string giving the timezone, a second line
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.q "\*- \*- \fIinterval\fP"
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describing the time interval before the first transition if any, and
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zero or more following lines
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.q "\fIdate time interval\fP",
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one line for each transition time and following interval. Fields are
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separated by single tabs.
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.PP
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Dates are in
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.IR yyyy - mm - dd
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format and times are in 24-hour
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.IR hh : mm : ss
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format where
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.IR hh <24.
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Times are in local time immediately after the transition. A
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time interval description consists of a UT offset in signed
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.RI \(+- hhmmss
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format, a time zone abbreviation, and an isdst flag. An abbreviation
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that equals the UT offset is omitted; other abbreviations are
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double-quoted strings unless they consist of one or more alphabetic
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characters. An isdst flag is omitted for standard time, and otherwise
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is a decimal integer that is unsigned and positive (typically 1) for
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daylight saving time and negative for unknown.
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.PP
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In times and in UT offsets with absolute value less than 100 hours,
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the seconds are omitted if they are zero, and
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the minutes are also omitted if they are also zero. Positive UT
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offsets are east of Greenwich. The UT offset \*-00 denotes a UT
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placeholder in areas where the actual offset is unspecified; by
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convention, this occurs when the UT offset is zero and the time zone
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abbreviation begins with
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.q "\*-"
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or is
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.q "zzz".
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.PP
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In double-quoted strings, escape sequences represent unusual
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characters. The escape sequences are \es for space, and \e", \e\e,
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\ef, \en, \er, \et, and \ev with their usual meaning in the C
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programming language. E.g., the double-quoted string
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\*(lq"CET\es\e"\e\e"\*(rq represents the character sequence \*(lqCET
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"\e\*(rq.\""
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.PP
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.ne 9
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Here is an example of the output, with the leading empty line omitted.
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(This example is shown with tab stops set far enough apart so that the
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tabbed columns line up.)
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.nf
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.sp
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.if \n(.g .ft CW
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.if t .in +.5i
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.if n .in +2
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.nr w \w'1896-01-13 'u+\n(.i
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.ta \w'1896-01-13 'u +\w'12:01:26 'u +\w'-103126 'u +\w'HWT 'u
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TZ="Pacific/Honolulu"
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- - -103126 LMT
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1896-01-13 12:01:26 -1030 HST
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1933-04-30 03 -0930 HDT 1
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1933-05-21 11 -1030 HST
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1942-02-09 03 -0930 HWT 1
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1945-08-14 13:30 -0930 HPT 1
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1945-09-30 01 -1030 HST
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1947-06-08 02:30 -10 HST
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.in
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.if \n(.g .ft
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.sp
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.fi
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Here, local time begins 10 hours, 31 minutes and 26 seconds west of
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UT, and is a standard time abbreviated LMT. Immediately after the
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first transition, the date is 1896-01-13 and the time is 12:01:26, and
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the following time interval is 10.5 hours west of UT, a standard time
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abbreviated HST. Immediately after the second transition, the date is
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1933-04-30 and the time is 03:00:00 and the following time interval is
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9.5 hours west of UT, is abbreviated HDT, and is daylight saving time.
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Immediately after the last transition the date is 1947-06-08 and the
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time is 02:30:00, and the following time interval is 10 hours west of
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UT, a standard time abbreviated HST.
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.PP
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.ne 10
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Here are excerpts from another example:
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.nf
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.sp
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.if \n(.g .ft CW
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.if t .in +.5i
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.if n .in +2
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TZ="Europe/Astrakhan"
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- - +031212 LMT
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1924-04-30 23:47:48 +03
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1930-06-21 01 +04
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1981-04-01 01 +05 1
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1981-09-30 23 +04
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\&...
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2014-10-26 01 +03
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2016-03-27 03 +04
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.in
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.if \n(.g .ft
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.sp
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.fi
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This time zone is east of UT, so its UT offsets are positive. Also,
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many of its time zone abbreviations are omitted since they duplicate
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the text of the UT offset.
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.SH LIMITATIONS
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Time discontinuities are found by sampling the results returned by localtime
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at twelve-hour intervals.
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This works in all real-world cases;
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one can construct artificial time zones for which this fails.
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.PP
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In the
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.B \*-v
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and
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.B \*-V
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output,
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.q "UT"
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denotes the value returned by
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.BR gmtime (3),
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which uses UTC for modern timestamps and some other UT flavor for
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timestamps that predate the introduction of UTC.
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No attempt is currently made to have the output use
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.q "UTC"
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for newer and
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.q "UT"
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for older timestamps, partly because the exact date of the
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introduction of UTC is problematic.
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.SH SEE ALSO
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.BR tzfile (5),
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.BR zic (8)
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.\" This file is in the public domain, so clarified as of
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.\" 2009-05-17 by Arthur David Olson.
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