2 .\" This file is in the public domain, so clarified as of
3 .\" 1996-06-05 by Arthur David Olson <arthur_david_olson@nih.gov>.
4 .TH TZFILE 5 2012-05-04 "" "Linux Programmer's Manual"
6 tzfile \- timezone information
8 This page describes the structure of the timezone files used by
10 These files are typically found under one of the directories
13 .IR /usr/share/zoneinfo .
15 Timezone information files
16 begin with the magic characters "TZif" to identify them as
17 timezone information files,
18 followed by a character identifying the version of the file's format
19 (as of 2005, either an ASCII NUL (\(aq\\0\(aq) or a \(aq2\(aq)
20 followed by fifteen bytes containing zeros reserved for future use,
21 followed by six four-byte values of type
23 written in a "standard" byte order
24 (the high-order byte of the value is written first).
29 The number of UTC/local indicators stored in the file.
32 The number of standard/wall indicators stored in the file.
35 The number of leap seconds for which data is stored in the file.
38 The number of "transition times" for which data is stored
42 The number of "local time types" for which data is stored
43 in the file (must not be zero).
46 The number of characters of "timezone abbreviation strings"
49 The above header is followed by
51 four-byte values of type
53 sorted in ascending order.
54 These values are written in "standard" byte order.
55 Each is used as a transition time (as returned by
57 at which the rules for computing local time change.
60 one-byte values of type
62 each one tells which of the different types of "local time" types
63 described in the file is associated with the same-indexed transition time.
64 These values serve as indices into an array of
68 entries) that appear next in the file;
69 these structures are defined as follows:
76 unsigned int tt_abbrind;
81 Each structure is written as a four-byte value for
85 in a standard byte order, followed by a one-byte value for
87 and a one-byte value for
91 gives the number of seconds to be added to UTC,
99 serves as an index into the array of timezone abbreviation characters
102 structure(s) in the file.
106 pairs of four-byte values, written in standard byte order;
107 the first value of each pair gives the time
110 at which a leap second occurs;
113 number of leap seconds to be applied after the given time.
114 The pairs of values are sorted in ascending order by time.
118 standard/wall indicators, each stored as a one-byte value;
119 they tell whether the transition times associated with local time types
120 were specified as standard time or wall clock time,
121 and are used when a timezone file is used in handling POSIX-style
122 timezone environment variables.
126 UTC/local indicators, each stored as a one-byte value;
127 they tell whether the transition times associated with local time types
128 were specified as UTC or local time,
129 and are used when a timezone file is used in handling POSIX-style
130 timezone environment variables.
133 uses the first standard-time
135 structure in the file
138 structure in the absence of a standard-time structure)
141 is zero or the time argument is less than the first transition time recorded
144 For version-2-format timezone files,
145 the above header and data is followed by a second header and data,
146 identical in format except that
147 eight bytes are used for each transition time or leap-second time.
148 After the second header and data comes a newline-enclosed,
149 POSIX-TZ-environment-variable-style string for use in handling instants
150 after the last transition time stored in the file
151 (with nothing between the newlines if there is no POSIX representation for
159 in the glibc source code.