]>
Commit | Line | Data |
---|---|---|
fea681da MK |
1 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
2 | .\" | |
93015253 | 3 | .\" %%%LICENSE_START(VERBATIM) |
fea681da MK |
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 | .\" |
fea681da MK |
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14 | .\" manual page may be incorrect or out-of-date.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 | .\" |
fea681da MK |
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 | |
b30b425b MK |
80 | .BR tzfile (5) |
81 | format to | |
2c7f2006 J |
82 | .IR /etc/localtime . |
83 | A timezone database of these files may be located in the system | |
84 | timezone directory (see the \fBFILES\fP section below). | |
fea681da | 85 | .PP |
097585ed MK |
86 | If the |
87 | .B TZ | |
343d1314 | 88 | variable does appear in the environment, but its value is empty, |
fea681da | 89 | or its value cannot be interpreted using any of the formats specified |
343d1314 | 90 | below, then Coordinated Universal Time (UTC) is used. |
fea681da | 91 | .PP |
097585ed MK |
92 | The value of |
93 | .B TZ | |
411dded2 WP |
94 | can be one of two formats. |
95 | The first format is a string of characters that directly represent the | |
96 | timezone to be used: | |
bdd915e2 MK |
97 | .PP |
98 | .in +4n | |
99 | .EX | |
a288791d | 100 | .IR "std offset" [ dst [ offset ][, start [ /time ], end [ /time ]]] |
bdd915e2 MK |
101 | .EE |
102 | .in | |
103 | .PP | |
520d6ed0 | 104 | There are no spaces in the specification. |
4faf9583 | 105 | The \fIstd\fP string specifies an abbreviation for the timezone and must be |
c13182ef | 106 | three or more alphabetic characters. |
4faf9583 WP |
107 | When enclosed between the less-than (<) and greater-than (>) signs, the |
108 | characters set is expanded to include the plus (+) sign, the minus (-) | |
109 | sign, and digits. | |
c13182ef | 110 | The \fIoffset\fP string immediately |
fea681da | 111 | follows \fIstd\fP and specifies the time value to be added to the local |
c13182ef MK |
112 | time to get Coordinated Universal Time (UTC). |
113 | The \fIoffset\fP is positive | |
5b0dc1ba | 114 | if the local timezone is west of the Prime Meridian and negative if it is |
c13182ef | 115 | east. |
036ea825 | 116 | The hour must be between 0 and 24, and the minutes and seconds 00 and 59: |
bdd915e2 MK |
117 | .PP |
118 | .in +4n | |
119 | .EX | |
036ea825 | 120 | .RI [ + | - ] hh [ :mm [ :ss ]] |
bdd915e2 MK |
121 | .EE |
122 | .in | |
fea681da | 123 | .PP |
c13182ef | 124 | The \fIdst\fP string and \fIoffset\fP specify the name and offset for the |
5b0dc1ba | 125 | corresponding daylight saving timezone. |
c13182ef | 126 | If the offset is omitted, |
343d1314 | 127 | it defaults to one hour ahead of standard time. |
fea681da | 128 | .PP |
e2905dc1 | 129 | The \fIstart\fP field specifies when daylight saving time goes into |
fea681da | 130 | effect and the \fIend\fP field specifies when the change is made back to |
c13182ef MK |
131 | standard time. |
132 | These fields may have the following formats: | |
fea681da MK |
133 | .TP |
134 | J\fIn\fP | |
c13182ef | 135 | This specifies the Julian day with \fIn\fP between 1 and 365. |
567e764a MK |
136 | Leap days are not counted. |
137 | In this format, February 29 can't be represented; | |
138 | February 28 is day 59, and March 1 is always day 60. | |
c13182ef | 139 | .TP |
fea681da | 140 | .I n |
567e764a | 141 | This specifies the zero-based Julian day with \fIn\fP between 0 and 365. |
c13182ef MK |
142 | February 29 is counted in leap years. |
143 | .TP | |
fea681da | 144 | M\fIm\fP.\fIw\fP.\fId\fP |
c13182ef MK |
145 | This specifies day \fId\fP (0 <= \fId\fP <= 6) of week \fIw\fP |
146 | (1 <= \fIw\fP <= 5) of month \fIm\fP (1 <= \fIm\fP <= 12). | |
147 | Week 1 is | |
148 | the first week in which day \fId\fP occurs and week 5 is the last week | |
149 | in which day \fId\fP occurs. | |
150 | Day 0 is a Sunday. | |
fea681da MK |
151 | .PP |
152 | The \fItime\fP fields specify when, in the local time currently in effect, | |
c13182ef MK |
153 | the change to the other time occurs. |
154 | If omitted, the default is 02:00:00. | |
847e0d88 | 155 | .PP |
c13182ef MK |
156 | Here is an example for New Zealand, |
157 | where the standard time (NZST) is 12 hours ahead of UTC, | |
158 | and daylight saving time (NZDT), 13 hours ahead of UTC, | |
e2905dc1 MK |
159 | runs from the first Sunday in October to the third Sunday in March, |
160 | and the changeovers happen at the default time of 02:00:00: | |
bdd915e2 MK |
161 | .in +4n |
162 | .EX | |
163 | TZ="NZST-12:00:00NZDT-13:00:00,M10.1.0,M3.3.0" | |
164 | .EE | |
165 | .in | |
fea681da | 166 | .PP |
411dded2 | 167 | The second format specifies that the timezone information should be read |
fea681da | 168 | from a file: |
bdd915e2 MK |
169 | .PP |
170 | .in +4n | |
171 | .EX | |
fea681da | 172 | :[filespec] |
bdd915e2 MK |
173 | .EE |
174 | .in | |
175 | .PP | |
4e00a0b8 J |
176 | If the file specification \fIfilespec\fP is omitted, or its value cannot |
177 | be interpreted, then Coordinated Universal Time (UTC) is used. | |
c13182ef | 178 | If \fIfilespec\fP is given, it specifies another |
fea681da | 179 | .BR tzfile (5)-format |
5b0dc1ba | 180 | file to read the timezone information from. |
f81fb444 | 181 | If \fIfilespec\fP does not begin with a \(aq/\(aq, the file specification is |
f2671085 MK |
182 | relative to the system timezone directory. |
183 | If the colon is omitted each | |
411dded2 | 184 | of the above \fBTZ\fP formats will be tried. |
e2905dc1 MK |
185 | .PP |
186 | Here's an example, once more for New Zealand: | |
bdd915e2 MK |
187 | .PP |
188 | .in +4n | |
189 | .EX | |
190 | TZ=":Pacific/Auckland" | |
191 | .EE | |
192 | .in | |
c1e90e15 WP |
193 | .SH ENVIRONMENT |
194 | .TP | |
195 | .B TZ | |
196 | If this variable is set its value takes precedence over the system | |
197 | configured timezone. | |
198 | .TP | |
199 | .B TZDIR | |
200 | If this variable is set its value takes precedence over the system | |
201 | configured timezone database directory path. | |
fea681da | 202 | .SH FILES |
c1e90e15 | 203 | .TP |
feb9265d | 204 | .I /etc/localtime |
c1e90e15 WP |
205 | The system timezone file. |
206 | .TP | |
feb9265d | 207 | .I /usr/share/zoneinfo/ |
c1e90e15 WP |
208 | The system timezone database directory. |
209 | .TP | |
feb9265d | 210 | .I /usr/share/zoneinfo/posixrules |
1cec674c WP |
211 | When a TZ string includes a dst timezone without anything following it, |
212 | then this file is used for the start/end rules. | |
213 | It is in the | |
b30b425b MK |
214 | .BR tzfile (5) |
215 | format. | |
1cec674c WP |
216 | By default, the zoneinfo Makefile hard links it to the |
217 | .IR America/New_York " tzfile." | |
c1e90e15 WP |
218 | .PP |
219 | Above are the current standard file locations, but they are | |
220 | configurable when glibc is compiled. | |
1a14cdb6 PH |
221 | .SH ATTRIBUTES |
222 | For an explanation of the terms used in this section, see | |
223 | .BR attributes (7). | |
224 | .TS | |
225 | allbox; | |
226 | lb lb lb | |
227 | l l l. | |
228 | Interface Attribute Value | |
229 | T{ | |
230 | .BR tzset () | |
231 | T} Thread safety MT-Safe env locale | |
232 | .TE | |
47297adb | 233 | .SH CONFORMING TO |
595652e0 | 234 | POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. |
fea681da | 235 | .SH NOTES |
dd3568a1 | 236 | .PP |
122dff10 MK |
237 | 4.3BSD had a function |
238 | .BI "char *timezone(" zone ", " dst ) | |
239 | that returned the | |
5b0dc1ba | 240 | name of the timezone corresponding to its first argument (minutes |
750d65df | 241 | West of UTC). |
c13182ef | 242 | If the second argument was 0, the standard name was used, |
e2905dc1 | 243 | otherwise the daylight saving time version. |
47297adb | 244 | .SH SEE ALSO |
fea681da MK |
245 | .BR date (1), |
246 | .BR gettimeofday (2), | |
247 | .BR time (2), | |
248 | .BR ctime (3), | |
249 | .BR getenv (3), | |
250 | .BR tzfile (5) |