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1 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
2 | .\" | |
93015253 | 3 | .\" %%%LICENSE_START(VERBATIM) |
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4 | .\" Permission is granted to make and distribute verbatim copies of this |
5 | .\" manual provided the copyright notice and this permission notice are | |
6 | .\" preserved on all copies. | |
7 | .\" | |
8 | .\" Permission is granted to copy and distribute modified versions of this | |
9 | .\" manual under the conditions for verbatim copying, provided that the | |
10 | .\" entire resulting derived work is distributed under the terms of a | |
11 | .\" permission notice identical to this one. | |
c13182ef | 12 | .\" |
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13 | .\" Since the Linux kernel and libraries are constantly changing, this |
14 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
15 | .\" responsibility for errors or omissions, or for damages resulting from | |
16 | .\" the use of the information contained herein. The author(s) may not | |
17 | .\" have taken the same level of care in the production of this manual, | |
18 | .\" which is licensed free of charge, as they might when working | |
19 | .\" professionally. | |
c13182ef | 20 | .\" |
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21 | .\" Formatted or processed versions of this manual, if unaccompanied by |
22 | .\" the source, must acknowledge the copyright and authors of this work. | |
4b72fb64 | 23 | .\" %%%LICENSE_END |
fea681da MK |
24 | .\" |
25 | .\" References consulted: | |
26 | .\" Linux libc source code | |
27 | .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) | |
28 | .\" 386BSD man pages | |
29 | .\" Modified Sun Jul 25 11:01:58 1993 by Rik Faith (faith@cs.unc.edu) | |
30 | .\" Modified 2001-11-13, aeb | |
122dff10 MK |
31 | .\" Modified 2004-12-01 mtk and Martin Schulze <joey@infodrom.org> |
32 | .\" | |
4b8c67d9 | 33 | .TH TZSET 3 2017-09-15 "" "Linux Programmer's Manual" |
fea681da MK |
34 | .SH NAME |
35 | tzset, tzname, timezone, daylight \- initialize time conversion information | |
36 | .SH SYNOPSIS | |
37 | .nf | |
38 | .B #include <time.h> | |
68e4db0a | 39 | .PP |
fea681da | 40 | .B void tzset (void); |
68e4db0a | 41 | .PP |
fea681da MK |
42 | .BI "extern char *" tzname [2]; |
43 | .BI "extern long " timezone ; | |
44 | .BI "extern int " daylight ; | |
45 | .fi | |
68e4db0a | 46 | .PP |
cc4615cc MK |
47 | .in -4n |
48 | Feature Test Macro Requirements for glibc (see | |
49 | .BR feature_test_macros (7)): | |
50 | .in | |
68e4db0a | 51 | .PP |
cc4615cc | 52 | .BR tzset (): |
cff459de | 53 | _POSIX_C_SOURCE |
cc4615cc MK |
54 | .br |
55 | .IR tzname : | |
cff459de | 56 | _POSIX_C_SOURCE |
cc4615cc | 57 | .br |
d59161f9 | 58 | .IR timezone , |
cc4615cc | 59 | .IR daylight : |
d59161f9 MK |
60 | _XOPEN_SOURCE |
61 | || /* Glibc since 2.19: */ _DEFAULT_SOURCE | |
62 | || /* Glibc versions <= 2.19: */ _SVID_SOURCE | |
fea681da | 63 | .SH DESCRIPTION |
60a90ecd MK |
64 | The |
65 | .BR tzset () | |
66 | function initializes the \fItzname\fP variable from the | |
097585ed MK |
67 | .B TZ |
68 | environment variable. | |
c13182ef | 69 | This function is automatically called by the |
5b0dc1ba | 70 | other time conversion functions that depend on the timezone. |
464ba7fc | 71 | In a System-V-like environment, it will also set the variables \fItimezone\fP |
750d65df | 72 | (seconds West of UTC) and \fIdaylight\fP (to 0 if this timezone does not |
17e9724a CD |
73 | have any daylight saving time rules, or to nonzero if there is a time, |
74 | past, present or future when daylight saving time applies). | |
fea681da | 75 | .PP |
097585ed MK |
76 | If the |
77 | .B TZ | |
2c7f2006 J |
78 | variable does not appear in the environment, the system timezone is used. |
79 | The system timezone is configured by copying, or linking, a file in the | |
80 | .BR tzfile "(5) format to" | |
81 | .IR /etc/localtime . | |
82 | A timezone database of these files may be located in the system | |
83 | timezone directory (see the \fBFILES\fP section below). | |
fea681da | 84 | .PP |
097585ed MK |
85 | If the |
86 | .B TZ | |
343d1314 | 87 | variable does appear in the environment, but its value is empty, |
fea681da | 88 | or its value cannot be interpreted using any of the formats specified |
343d1314 | 89 | below, then Coordinated Universal Time (UTC) is used. |
fea681da | 90 | .PP |
097585ed MK |
91 | The value of |
92 | .B TZ | |
411dded2 WP |
93 | can be one of two formats. |
94 | The first format is a string of characters that directly represent the | |
95 | timezone to be used: | |
bdd915e2 MK |
96 | .PP |
97 | .in +4n | |
98 | .EX | |
a288791d | 99 | .IR "std offset" [ dst [ offset ][, start [ /time ], end [ /time ]]] |
bdd915e2 MK |
100 | .EE |
101 | .in | |
102 | .PP | |
520d6ed0 | 103 | There are no spaces in the specification. |
4faf9583 | 104 | The \fIstd\fP string specifies an abbreviation for the timezone and must be |
c13182ef | 105 | three or more alphabetic characters. |
4faf9583 WP |
106 | When enclosed between the less-than (<) and greater-than (>) signs, the |
107 | characters set is expanded to include the plus (+) sign, the minus (-) | |
108 | sign, and digits. | |
c13182ef | 109 | The \fIoffset\fP string immediately |
fea681da | 110 | follows \fIstd\fP and specifies the time value to be added to the local |
c13182ef MK |
111 | time to get Coordinated Universal Time (UTC). |
112 | The \fIoffset\fP is positive | |
5b0dc1ba | 113 | if the local timezone is west of the Prime Meridian and negative if it is |
c13182ef | 114 | east. |
036ea825 | 115 | The hour must be between 0 and 24, and the minutes and seconds 00 and 59: |
bdd915e2 MK |
116 | .PP |
117 | .in +4n | |
118 | .EX | |
036ea825 | 119 | .RI [ + | - ] hh [ :mm [ :ss ]] |
bdd915e2 MK |
120 | .EE |
121 | .in | |
fea681da | 122 | .PP |
c13182ef | 123 | The \fIdst\fP string and \fIoffset\fP specify the name and offset for the |
5b0dc1ba | 124 | corresponding daylight saving timezone. |
c13182ef | 125 | If the offset is omitted, |
343d1314 | 126 | it defaults to one hour ahead of standard time. |
fea681da | 127 | .PP |
e2905dc1 | 128 | The \fIstart\fP field specifies when daylight saving time goes into |
fea681da | 129 | effect and the \fIend\fP field specifies when the change is made back to |
c13182ef MK |
130 | standard time. |
131 | These fields may have the following formats: | |
fea681da MK |
132 | .TP |
133 | J\fIn\fP | |
c13182ef | 134 | This specifies the Julian day with \fIn\fP between 1 and 365. |
567e764a MK |
135 | Leap days are not counted. |
136 | In this format, February 29 can't be represented; | |
137 | February 28 is day 59, and March 1 is always day 60. | |
c13182ef | 138 | .TP |
fea681da | 139 | .I n |
567e764a | 140 | This specifies the zero-based Julian day with \fIn\fP between 0 and 365. |
c13182ef MK |
141 | February 29 is counted in leap years. |
142 | .TP | |
fea681da | 143 | M\fIm\fP.\fIw\fP.\fId\fP |
c13182ef MK |
144 | This specifies day \fId\fP (0 <= \fId\fP <= 6) of week \fIw\fP |
145 | (1 <= \fIw\fP <= 5) of month \fIm\fP (1 <= \fIm\fP <= 12). | |
146 | Week 1 is | |
147 | the first week in which day \fId\fP occurs and week 5 is the last week | |
148 | in which day \fId\fP occurs. | |
149 | Day 0 is a Sunday. | |
fea681da MK |
150 | .PP |
151 | The \fItime\fP fields specify when, in the local time currently in effect, | |
c13182ef MK |
152 | the change to the other time occurs. |
153 | If omitted, the default is 02:00:00. | |
847e0d88 | 154 | .PP |
c13182ef MK |
155 | Here is an example for New Zealand, |
156 | where the standard time (NZST) is 12 hours ahead of UTC, | |
157 | and daylight saving time (NZDT), 13 hours ahead of UTC, | |
e2905dc1 MK |
158 | runs from the first Sunday in October to the third Sunday in March, |
159 | and the changeovers happen at the default time of 02:00:00: | |
bdd915e2 MK |
160 | .in +4n |
161 | .EX | |
162 | TZ="NZST-12:00:00NZDT-13:00:00,M10.1.0,M3.3.0" | |
163 | .EE | |
164 | .in | |
fea681da | 165 | .PP |
411dded2 | 166 | The second format specifies that the timezone information should be read |
fea681da | 167 | from a file: |
bdd915e2 MK |
168 | .PP |
169 | .in +4n | |
170 | .EX | |
fea681da | 171 | :[filespec] |
bdd915e2 MK |
172 | .EE |
173 | .in | |
174 | .PP | |
4e00a0b8 J |
175 | If the file specification \fIfilespec\fP is omitted, or its value cannot |
176 | be interpreted, then Coordinated Universal Time (UTC) is used. | |
c13182ef | 177 | If \fIfilespec\fP is given, it specifies another |
fea681da | 178 | .BR tzfile (5)-format |
5b0dc1ba | 179 | file to read the timezone information from. |
f81fb444 | 180 | If \fIfilespec\fP does not begin with a \(aq/\(aq, the file specification is |
f2671085 MK |
181 | relative to the system timezone directory. |
182 | If the colon is omitted each | |
411dded2 | 183 | of the above \fBTZ\fP formats will be tried. |
e2905dc1 MK |
184 | .PP |
185 | Here's an example, once more for New Zealand: | |
bdd915e2 MK |
186 | .PP |
187 | .in +4n | |
188 | .EX | |
189 | TZ=":Pacific/Auckland" | |
190 | .EE | |
191 | .in | |
c1e90e15 WP |
192 | .SH ENVIRONMENT |
193 | .TP | |
194 | .B TZ | |
195 | If this variable is set its value takes precedence over the system | |
196 | configured timezone. | |
197 | .TP | |
198 | .B TZDIR | |
199 | If this variable is set its value takes precedence over the system | |
200 | configured timezone database directory path. | |
fea681da | 201 | .SH FILES |
c1e90e15 | 202 | .TP |
feb9265d | 203 | .I /etc/localtime |
c1e90e15 WP |
204 | The system timezone file. |
205 | .TP | |
feb9265d | 206 | .I /usr/share/zoneinfo/ |
c1e90e15 WP |
207 | The system timezone database directory. |
208 | .TP | |
feb9265d | 209 | .I /usr/share/zoneinfo/posixrules |
1cec674c WP |
210 | When a TZ string includes a dst timezone without anything following it, |
211 | then this file is used for the start/end rules. | |
212 | It is in the | |
213 | .BR tzfile "(5) format." | |
214 | By default, the zoneinfo Makefile hard links it to the | |
215 | .IR America/New_York " tzfile." | |
c1e90e15 WP |
216 | .PP |
217 | Above are the current standard file locations, but they are | |
218 | configurable when glibc is compiled. | |
1a14cdb6 PH |
219 | .SH ATTRIBUTES |
220 | For an explanation of the terms used in this section, see | |
221 | .BR attributes (7). | |
222 | .TS | |
223 | allbox; | |
224 | lb lb lb | |
225 | l l l. | |
226 | Interface Attribute Value | |
227 | T{ | |
228 | .BR tzset () | |
229 | T} Thread safety MT-Safe env locale | |
230 | .TE | |
47297adb | 231 | .SH CONFORMING TO |
595652e0 | 232 | POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. |
fea681da | 233 | .SH NOTES |
dd3568a1 | 234 | .PP |
122dff10 MK |
235 | 4.3BSD had a function |
236 | .BI "char *timezone(" zone ", " dst ) | |
237 | that returned the | |
5b0dc1ba | 238 | name of the timezone corresponding to its first argument (minutes |
750d65df | 239 | West of UTC). |
c13182ef | 240 | If the second argument was 0, the standard name was used, |
e2905dc1 | 241 | otherwise the daylight saving time version. |
47297adb | 242 | .SH SEE ALSO |
fea681da MK |
243 | .BR date (1), |
244 | .BR gettimeofday (2), | |
245 | .BR time (2), | |
246 | .BR ctime (3), | |
247 | .BR getenv (3), | |
248 | .BR tzfile (5) |