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a1eaacb1 | 1 | '\" t |
fea681da MK |
2 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
3 | .\" | |
5fbde956 | 4 | .\" SPDX-License-Identifier: Linux-man-pages-copyleft |
fea681da MK |
5 | .\" |
6 | .\" References consulted: | |
7 | .\" Linux libc source code | |
8 | .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) | |
9 | .\" 386BSD man pages | |
10 | .\" Modified Sun Jul 25 11:01:58 1993 by Rik Faith (faith@cs.unc.edu) | |
11 | .\" Modified 2001-11-13, aeb | |
122dff10 MK |
12 | .\" Modified 2004-12-01 mtk and Martin Schulze <joey@infodrom.org> |
13 | .\" | |
4c1c5274 | 14 | .TH tzset 3 (date) "Linux man-pages (unreleased)" |
fea681da MK |
15 | .SH NAME |
16 | tzset, tzname, timezone, daylight \- initialize time conversion information | |
e3c03811 AC |
17 | .SH LIBRARY |
18 | Standard C library | |
8fc3b2cf | 19 | .RI ( libc ", " \-lc ) |
fea681da MK |
20 | .SH SYNOPSIS |
21 | .nf | |
22 | .B #include <time.h> | |
c6d039a3 | 23 | .P |
2faa0fbd | 24 | .B void tzset(void); |
c6d039a3 | 25 | .P |
fea681da MK |
26 | .BI "extern char *" tzname [2]; |
27 | .BI "extern long " timezone ; | |
28 | .BI "extern int " daylight ; | |
29 | .fi | |
c6d039a3 | 30 | .P |
d39ad78f | 31 | .RS -4 |
cc4615cc MK |
32 | Feature Test Macro Requirements for glibc (see |
33 | .BR feature_test_macros (7)): | |
d39ad78f | 34 | .RE |
c6d039a3 | 35 | .P |
cc4615cc | 36 | .BR tzset (): |
1dd0d7b4 MK |
37 | .nf |
38 | _POSIX_C_SOURCE | |
39 | .fi | |
c6d039a3 | 40 | .P |
cc4615cc | 41 | .IR tzname : |
1dd0d7b4 MK |
42 | .nf |
43 | _POSIX_C_SOURCE | |
44 | .fi | |
c6d039a3 | 45 | .P |
d59161f9 | 46 | .IR timezone , |
cc4615cc | 47 | .IR daylight : |
db198f06 MK |
48 | .nf |
49 | _XOPEN_SOURCE | |
75c018a1 AC |
50 | || /* glibc >= 2.19: */ _DEFAULT_SOURCE |
51 | || /* glibc <= 2.19: */ _SVID_SOURCE | |
db198f06 | 52 | .fi |
fea681da | 53 | .SH DESCRIPTION |
60a90ecd MK |
54 | The |
55 | .BR tzset () | |
56 | function initializes the \fItzname\fP variable from the | |
097585ed MK |
57 | .B TZ |
58 | environment variable. | |
c13182ef | 59 | This function is automatically called by the |
5b0dc1ba | 60 | other time conversion functions that depend on the timezone. |
464ba7fc | 61 | In a System-V-like environment, it will also set the variables \fItimezone\fP |
750d65df | 62 | (seconds West of UTC) and \fIdaylight\fP (to 0 if this timezone does not |
17e9724a | 63 | have any daylight saving time rules, or to nonzero if there is a time, |
735334d4 | 64 | past, present, or future when daylight saving time applies). |
c6d039a3 | 65 | .P |
097585ed MK |
66 | If the |
67 | .B TZ | |
2c7f2006 J |
68 | variable does not appear in the environment, the system timezone is used. |
69 | The system timezone is configured by copying, or linking, a file in the | |
b30b425b MK |
70 | .BR tzfile (5) |
71 | format to | |
2c7f2006 J |
72 | .IR /etc/localtime . |
73 | A timezone database of these files may be located in the system | |
74 | timezone directory (see the \fBFILES\fP section below). | |
c6d039a3 | 75 | .P |
097585ed MK |
76 | If the |
77 | .B TZ | |
343d1314 | 78 | variable does appear in the environment, but its value is empty, |
fea681da | 79 | or its value cannot be interpreted using any of the formats specified |
343d1314 | 80 | below, then Coordinated Universal Time (UTC) is used. |
c6d039a3 | 81 | .P |
097585ed MK |
82 | The value of |
83 | .B TZ | |
411dded2 WP |
84 | can be one of two formats. |
85 | The first format is a string of characters that directly represent the | |
86 | timezone to be used: | |
c6d039a3 | 87 | .P |
bdd915e2 MK |
88 | .in +4n |
89 | .EX | |
a288791d | 90 | .IR "std offset" [ dst [ offset ][, start [ /time ], end [ /time ]]] |
bdd915e2 MK |
91 | .EE |
92 | .in | |
c6d039a3 | 93 | .P |
520d6ed0 | 94 | There are no spaces in the specification. |
4faf9583 | 95 | The \fIstd\fP string specifies an abbreviation for the timezone and must be |
c13182ef | 96 | three or more alphabetic characters. |
4faf9583 | 97 | When enclosed between the less-than (<) and greater-than (>) signs, the |
78ab0ddf | 98 | character set is expanded to include the plus (+) sign, the minus (\-) |
4faf9583 | 99 | sign, and digits. |
c13182ef | 100 | The \fIoffset\fP string immediately |
fea681da | 101 | follows \fIstd\fP and specifies the time value to be added to the local |
c13182ef MK |
102 | time to get Coordinated Universal Time (UTC). |
103 | The \fIoffset\fP is positive | |
5b0dc1ba | 104 | if the local timezone is west of the Prime Meridian and negative if it is |
c13182ef | 105 | east. |
036ea825 | 106 | The hour must be between 0 and 24, and the minutes and seconds 00 and 59: |
c6d039a3 | 107 | .P |
bdd915e2 MK |
108 | .in +4n |
109 | .EX | |
d064d41a | 110 | .RI [ + | \- ] hh [ :mm [ :ss ]] |
bdd915e2 MK |
111 | .EE |
112 | .in | |
c6d039a3 | 113 | .P |
c13182ef | 114 | The \fIdst\fP string and \fIoffset\fP specify the name and offset for the |
5b0dc1ba | 115 | corresponding daylight saving timezone. |
c13182ef | 116 | If the offset is omitted, |
343d1314 | 117 | it defaults to one hour ahead of standard time. |
c6d039a3 | 118 | .P |
e2905dc1 | 119 | The \fIstart\fP field specifies when daylight saving time goes into |
fea681da | 120 | effect and the \fIend\fP field specifies when the change is made back to |
c13182ef MK |
121 | standard time. |
122 | These fields may have the following formats: | |
fea681da MK |
123 | .TP |
124 | J\fIn\fP | |
c13182ef | 125 | This specifies the Julian day with \fIn\fP between 1 and 365. |
567e764a MK |
126 | Leap days are not counted. |
127 | In this format, February 29 can't be represented; | |
128 | February 28 is day 59, and March 1 is always day 60. | |
c13182ef | 129 | .TP |
fea681da | 130 | .I n |
567e764a | 131 | This specifies the zero-based Julian day with \fIn\fP between 0 and 365. |
c13182ef MK |
132 | February 29 is counted in leap years. |
133 | .TP | |
fea681da | 134 | M\fIm\fP.\fIw\fP.\fId\fP |
c13182ef MK |
135 | This specifies day \fId\fP (0 <= \fId\fP <= 6) of week \fIw\fP |
136 | (1 <= \fIw\fP <= 5) of month \fIm\fP (1 <= \fIm\fP <= 12). | |
137 | Week 1 is | |
138 | the first week in which day \fId\fP occurs and week 5 is the last week | |
139 | in which day \fId\fP occurs. | |
140 | Day 0 is a Sunday. | |
c6d039a3 | 141 | .P |
fea681da | 142 | The \fItime\fP fields specify when, in the local time currently in effect, |
c13182ef MK |
143 | the change to the other time occurs. |
144 | If omitted, the default is 02:00:00. | |
c6d039a3 | 145 | .P |
c13182ef MK |
146 | Here is an example for New Zealand, |
147 | where the standard time (NZST) is 12 hours ahead of UTC, | |
148 | and daylight saving time (NZDT), 13 hours ahead of UTC, | |
e2905dc1 MK |
149 | runs from the first Sunday in October to the third Sunday in March, |
150 | and the changeovers happen at the default time of 02:00:00: | |
c6d039a3 | 151 | .P |
bdd915e2 MK |
152 | .in +4n |
153 | .EX | |
d064d41a | 154 | TZ="NZST\-12:00:00NZDT\-13:00:00,M10.1.0,M3.3.0" |
bdd915e2 MK |
155 | .EE |
156 | .in | |
c6d039a3 | 157 | .P |
411dded2 | 158 | The second format specifies that the timezone information should be read |
fea681da | 159 | from a file: |
c6d039a3 | 160 | .P |
bdd915e2 MK |
161 | .in +4n |
162 | .EX | |
fea681da | 163 | :[filespec] |
bdd915e2 MK |
164 | .EE |
165 | .in | |
c6d039a3 | 166 | .P |
4e00a0b8 J |
167 | If the file specification \fIfilespec\fP is omitted, or its value cannot |
168 | be interpreted, then Coordinated Universal Time (UTC) is used. | |
c13182ef | 169 | If \fIfilespec\fP is given, it specifies another |
fea681da | 170 | .BR tzfile (5)-format |
5b0dc1ba | 171 | file to read the timezone information from. |
b957f81f | 172 | If \fIfilespec\fP does not begin with a \[aq]/\[aq], the file specification is |
f2671085 MK |
173 | relative to the system timezone directory. |
174 | If the colon is omitted each | |
411dded2 | 175 | of the above \fBTZ\fP formats will be tried. |
c6d039a3 | 176 | .P |
e2905dc1 | 177 | Here's an example, once more for New Zealand: |
c6d039a3 | 178 | .P |
bdd915e2 MK |
179 | .in +4n |
180 | .EX | |
181 | TZ=":Pacific/Auckland" | |
182 | .EE | |
183 | .in | |
c1e90e15 WP |
184 | .SH ENVIRONMENT |
185 | .TP | |
186 | .B TZ | |
187 | If this variable is set its value takes precedence over the system | |
188 | configured timezone. | |
189 | .TP | |
190 | .B TZDIR | |
191 | If this variable is set its value takes precedence over the system | |
192 | configured timezone database directory path. | |
fea681da | 193 | .SH FILES |
c1e90e15 | 194 | .TP |
feb9265d | 195 | .I /etc/localtime |
c1e90e15 WP |
196 | The system timezone file. |
197 | .TP | |
feb9265d | 198 | .I /usr/share/zoneinfo/ |
c1e90e15 WP |
199 | The system timezone database directory. |
200 | .TP | |
feb9265d | 201 | .I /usr/share/zoneinfo/posixrules |
1cec674c WP |
202 | When a TZ string includes a dst timezone without anything following it, |
203 | then this file is used for the start/end rules. | |
204 | It is in the | |
b30b425b MK |
205 | .BR tzfile (5) |
206 | format. | |
1cec674c WP |
207 | By default, the zoneinfo Makefile hard links it to the |
208 | .IR America/New_York " tzfile." | |
c6d039a3 | 209 | .P |
c1e90e15 WP |
210 | Above are the current standard file locations, but they are |
211 | configurable when glibc is compiled. | |
1a14cdb6 PH |
212 | .SH ATTRIBUTES |
213 | For an explanation of the terms used in this section, see | |
214 | .BR attributes (7). | |
215 | .TS | |
216 | allbox; | |
c466875e | 217 | lbx lb lb |
1a14cdb6 PH |
218 | l l l. |
219 | Interface Attribute Value | |
220 | T{ | |
9e54434e BR |
221 | .na |
222 | .nh | |
1a14cdb6 PH |
223 | .BR tzset () |
224 | T} Thread safety MT-Safe env locale | |
225 | .TE | |
3113c7f3 | 226 | .SH STANDARDS |
4131356c AC |
227 | POSIX.1-2008. |
228 | .SH HISTORY | |
229 | POSIX.1-2001, SVr4, 4.3BSD. | |
c6d039a3 | 230 | .P |
122dff10 MK |
231 | 4.3BSD had a function |
232 | .BI "char *timezone(" zone ", " dst ) | |
233 | that returned the | |
5b0dc1ba | 234 | name of the timezone corresponding to its first argument (minutes |
750d65df | 235 | West of UTC). |
c13182ef | 236 | If the second argument was 0, the standard name was used, |
e2905dc1 | 237 | otherwise the daylight saving time version. |
47297adb | 238 | .SH SEE ALSO |
fea681da MK |
239 | .BR date (1), |
240 | .BR gettimeofday (2), | |
241 | .BR time (2), | |
242 | .BR ctime (3), | |
243 | .BR getenv (3), | |
244 | .BR tzfile (5) |