mirror of https://github.com/mkerrisk/man-pages
tzfile.5: Sync from tzdb upstream
This makes tzfile.5 a copy of the tzdb version, except that the tzdb version's first line is replaced by man-pages boilerplate. The new version documents version 3 format, among other things. Also, it removes the "Summary of the timezone information file format" section, which should no longer be needed due to improvements in the the part of the man page. Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Paul Eggert
Michael Kerrisk
parent
a581f7593b
commit
72942d65ad
4
Changes
4
Changes
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@ -33,3 +33,7 @@ Global changes
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Changes to individual pages
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---------------------------
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tzfile.5
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Paul Eggert
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Sync from tzdb version, to document version 3 format
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among other things.
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232
man5/tzfile.5
232
man5/tzfile.5
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@ -5,142 +5,148 @@
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.\"
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.\" @(#)tzfile.5 7.11
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.\"
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.TH TZFILE 5 2015-05-07 "" "Linux Programmer's Manual"
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.TH TZFILE 5 2017-08-04 "" "Linux Programmer's Manual"
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.SH NAME
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tzfile \- timezone information
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tzfile \- time zone information
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.SH DESCRIPTION
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This page describes the structure of the timezone files used by
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.BR tzset (3).
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These files are typically found under one of the directories
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.IR /usr/lib/zoneinfo
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or
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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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The time zone information files used by
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.BR tzset (3)
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are typically found under a directory with a name like
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.IR /usr/share/zoneinfo .
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Timezone information files begin with a 44-byte header structured as follows:
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.IP * 3
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The magic four-byte sequence
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"TZif" identifying this as a
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timezone information file.
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These files begin with a 44-byte header containing the following fields:
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.IP * 2
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The magic four-byte ASCII sequence
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.q "TZif"
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identifies the file as a time zone information file.
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.IP *
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A single character identifying the version of the file's format:
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either an ASCII NUL (\(aq\\0\(aq) or a \(aq2\(aq (\fB0x32\fP).
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A byte identifying the version of the file's format
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(as of 2017, either an ASCII NUL, or
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.q "2",
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or
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.q "3" ).
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.IP *
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Fifteen bytes containing zeros reserved for future use.
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.IP *
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Six four-byte values of type
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.IR long ,
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written in a "standard" byte order
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Six four-byte integer values
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written in a standard byte order
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(the high-order byte of the value is written first).
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These values are,
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in order:
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.RS
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.TP
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.I tzh_ttisgmtcnt
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The number of UTC/local indicators stored in the file.
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The number of UT/local indicators stored in the file.
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.TP
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.I tzh_ttisstdcnt
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The number of standard/wall indicators stored in the file.
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.TP
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.I tzh_leapcnt
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The number of leap seconds for which data is stored in the file.
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The number of leap seconds for which data entries are stored in the file.
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.TP
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.I tzh_timecnt
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The number of "transition times" for which data is stored
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The number of transition times for which data entries are stored
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in the file.
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.TP
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.I tzh_typecnt
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The number of "local time types" for which data is stored
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The number of local time types for which data entries are stored
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in the file (must not be zero).
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.TP
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.I tzh_charcnt
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The number of characters of "timezone abbreviation strings"
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The number of bytes of time zone abbreviation strings
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stored in the file.
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.RE
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.PP
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The above header is followed by
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The above header is followed by the following fields, whose lengths
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vary depend on the contents of the header:
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.IP * 2
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.I tzh_timecnt
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four-byte values of type
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.IR long ,
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sorted in ascending order.
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These values are written in "standard" byte order.
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four-byte signed integer values sorted in ascending order.
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These values are written in standard byte order.
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Each is used as a transition time (as returned by
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.BR time (2))
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at which the rules for computing local time change.
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Next come
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.IP *
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.I tzh_timecnt
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one-byte values of type
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.IR "unsigned char" ;
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each one tells which of the different types of "local time" types
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described in the file is associated with the same-indexed transition time.
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These values serve as indices into an array of
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.I ttinfo
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structures (with
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one-byte unsigned integer values;
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each one tells which of the different types of local time types
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described in the file is associated with the time period
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starting with the same-indexed transition time.
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These values serve as indices into the next field.
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.IP *
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.I tzh_typecnt
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entries) that appear next in the file;
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these structures are defined as follows:
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.in +4n
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.I ttinfo
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entries, each defined as follows:
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.in +.5i
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.sp
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.nf
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.ta .5i +\w'unsigned char\0\0'u
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struct ttinfo {
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long tt_gmtoff;
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int tt_isdst;
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unsigned int tt_abbrind;
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int32_t tt_gmtoff;
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unsigned char tt_isdst;
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unsigned char tt_abbrind;
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};
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.in
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.in -.5i
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.fi
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.sp
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Each structure is written as a four-byte value for
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.I tt_gmtoff
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of type
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.IR long ,
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Each structure is written as a four-byte signed integer value for
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.IR tt_gmtoff ,
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in a standard byte order, followed by a one-byte value for
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.I tt_isdst
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and a one-byte value for
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.IR tt_abbrind .
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In each structure,
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.I tt_gmtoff
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gives the number of seconds to be added to UTC,
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gives the number of seconds to be added to UT,
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.I tt_isdst
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tells whether
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.I tm_isdst
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should be set by
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.BR localtime (3),
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.BR localtime (3)
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and
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.I tt_abbrind
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serves as an index into the array of timezone abbreviation characters
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serves as an index into the array of time zone abbreviation bytes
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that follow the
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.I ttinfo
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structure(s) in the file.
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.PP
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Then there are
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.IP *
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.I tzh_leapcnt
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pairs of four-byte values, written in standard byte order;
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the first value of each pair gives the time
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the first value of each pair gives the nonnegative time
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(as returned by
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.BR time (2))
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at which a leap second occurs;
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the second gives the
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.I total
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number of leap seconds to be applied after the given time.
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number of leap seconds to be applied during the time period
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starting at the given time.
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The pairs of values are sorted in ascending order by time.
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.PP
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Then there are
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Each transition is for one leap second, either positive or negative;
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transitions always separated by at least 28 days minus 1 second.
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.IP *
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.I tzh_ttisstdcnt
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standard/wall indicators, each stored as a one-byte value;
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they tell whether the transition times associated with local time types
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were specified as standard time or wall clock time,
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and are used when a timezone file is used in handling POSIX-style
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timezone environment variables.
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.PP
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Finally, there are
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and are used when a time zone file is used in handling POSIX-style
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time zone environment variables.
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.IP *
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.I tzh_ttisgmtcnt
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UTC/local indicators, each stored as a one-byte value;
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UT/local indicators, each stored as a one-byte value;
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they tell whether the transition times associated with local time types
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were specified as UTC or local time,
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and are used when a timezone file is used in handling POSIX-style
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timezone environment variables.
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were specified as UT or local time,
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and are used when a time zone file is used in handling POSIX-style
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time zone environment variables.
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.PP
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The
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.BR localtime (3)
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function
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uses the first standard-time
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.I ttinfo
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structure in the file
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@ -152,84 +158,40 @@ if either
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is zero or the time argument is less than the first transition time recorded
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in the file.
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.SS Version 2 format
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For version-2-format timezone files,
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the above header and data is followed by a second header and data,
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For version-2-format time zone files,
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the above header and data are followed by a second header and data,
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identical in format except that
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eight bytes are used for each transition time or leap-second time
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(and that the version byte in the header record is
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\fB0x32\fP rather than \fB0x00\fP).
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eight bytes are used for each transition time or leap second time.
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(Leap second counts remain four bytes.)
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After the second header and data comes a newline-enclosed,
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POSIX-TZ-environment-variable-style string for use in handling instants
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after the last transition time stored in the file
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(with nothing between the newlines if there is no POSIX representation for
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such instants).
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The POSIX-style string must agree with the local time type after
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both data's last transition times; for example, given the string
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.q "WET0WEST,M3.5.0,M10.5.0/3"
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then if a last transition time is in July, the transition's local time
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type must specify a daylight-saving time abbreviated
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.q "WEST"
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that is one hour east of UT.
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.SS Version 3 format
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For version-3-format time zone files, the POSIX-TZ-style string may
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use two minor extensions to the POSIX TZ format, as described in
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.IR newtzset (3).
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First, the hours part of its transition times may be signed and range from
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\-167 through 167 instead of the POSIX-required unsigned values
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from 0 through 24. Second, DST is in effect all year if it starts
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January 1 at 00:00 and ends December 31 at 24:00 plus the difference
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between daylight saving and standard time.
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.PP
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The second section of the timezone file consists of another 44-byte header
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record, identical in structure to the one at the beginning of the file,
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except that it applies to the data that follows,
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which is also identical in structure
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to the first section of the timezone file, with the following differences:
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.IP * 3
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The transition time values, after the header, are eight-byte values.
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.IP *
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In each leap second record, the leap second value is an eight-byte value.
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The accumulated leap second count is still a four-byte value.
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.PP
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In all cases, the eight-byte time values are given in
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the "standard" byte order,
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the high-order byte first.
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.SS POSIX timezone string
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The second eight-byte time value section is followed by an optional
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third section:
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a single ASCII newline character (\(aq\\n\(aq),
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then a text string followed by a second
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newline character.
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The text string is a POSIX timezone string, whose format is described in the
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.BR tzset (3)
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manual page.
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.PP
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The POSIX timezone string defines a rule for computing transition times
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that follow the last transition time explicitly specified in the timezone
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information file.
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.SS Summary of the timezone information file format
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\&
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.RS
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.nf
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Four-byte value section
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(header version \fB0x00\fP or \fB0x32\fP)
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Header record
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Four-byte transition times
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Transition time index
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\fBttinfo\fP structures
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Timezone abbreviation array
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Leap second records
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Standard/Wall array
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UTC/Local array
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Eight-byte value section
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(only if first header version is \fB0x32\fP,
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the second header's version is also \fB0x32\fP)
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Header record
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Eight-byte transition times
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Transition time index
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\fBttinfo\fP structures
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Timezone abbreviation array
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Leap second records
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Standard/Wall array
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UTC/Local array
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Third section
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(optional, only in \fB0x32\fP version files)
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Newline character
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Timezone string
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Newline character
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.fi
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.RE
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.\"
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Future changes to the format may append more data.
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.SH SEE ALSO
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.BR ctime (3),
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.BR time (2),
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.BR localtime (3),
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.BR tzset (3),
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.BR tzselect (8),
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.I timezone/tzfile.h
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in the glibc source tree
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.BR zdump (8),
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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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.\" 1996-06-05 by Arthur David Olson.
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