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1 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
2 | .\" | |
3 | .\" Permission is granted to make and distribute verbatim copies of this | |
4 | .\" manual provided the copyright notice and this permission notice are | |
5 | .\" preserved on all copies. | |
6 | .\" | |
7 | .\" Permission is granted to copy and distribute modified versions of this | |
8 | .\" manual under the conditions for verbatim copying, provided that the | |
9 | .\" entire resulting derived work is distributed under the terms of a | |
10 | .\" permission notice identical to this one. | |
c13182ef | 11 | .\" |
fea681da MK |
12 | .\" Since the Linux kernel and libraries are constantly changing, this |
13 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
14 | .\" responsibility for errors or omissions, or for damages resulting from | |
15 | .\" the use of the information contained herein. The author(s) may not | |
16 | .\" have taken the same level of care in the production of this manual, | |
17 | .\" which is licensed free of charge, as they might when working | |
18 | .\" professionally. | |
c13182ef | 19 | .\" |
fea681da MK |
20 | .\" Formatted or processed versions of this manual, if unaccompanied by |
21 | .\" the source, must acknowledge the copyright and authors of this work. | |
22 | .\" | |
23 | .\" References consulted: | |
24 | .\" Linux libc source code | |
25 | .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) | |
26 | .\" 386BSD man pages | |
27 | .\" Modified Sun Jul 25 11:01:58 1993 by Rik Faith (faith@cs.unc.edu) | |
28 | .\" Modified 2001-11-13, aeb | |
122dff10 MK |
29 | .\" Modified 2004-12-01 mtk and Martin Schulze <joey@infodrom.org> |
30 | .\" | |
5a554f8e | 31 | .TH TZSET 3 2012-03-25 "" "Linux Programmer's Manual" |
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32 | .SH NAME |
33 | tzset, tzname, timezone, daylight \- initialize time conversion information | |
34 | .SH SYNOPSIS | |
35 | .nf | |
36 | .B #include <time.h> | |
37 | .sp | |
38 | .B void tzset (void); | |
39 | .sp | |
40 | .BI "extern char *" tzname [2]; | |
41 | .BI "extern long " timezone ; | |
42 | .BI "extern int " daylight ; | |
43 | .fi | |
cc4615cc MK |
44 | .sp |
45 | .in -4n | |
46 | Feature Test Macro Requirements for glibc (see | |
47 | .BR feature_test_macros (7)): | |
48 | .in | |
49 | .sp | |
50 | .BR tzset (): | |
0f200f07 | 51 | _POSIX_C_SOURCE\ >=\ 1 || _XOPEN_SOURCE || _POSIX_SOURCE |
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52 | .br |
53 | .IR tzname : | |
0f200f07 | 54 | _POSIX_C_SOURCE\ >=\ 1 || _XOPEN_SOURCE || _POSIX_SOURCE |
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55 | .br |
56 | .IR timezone : | |
57 | _SVID_SOURCE || _XOPEN_SOURCE | |
58 | .br | |
59 | .IR daylight : | |
60 | _SVID_SOURCE || _XOPEN_SOURCE | |
fea681da | 61 | .SH DESCRIPTION |
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62 | The |
63 | .BR tzset () | |
64 | function initializes the \fItzname\fP variable from the | |
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65 | .B TZ |
66 | environment variable. | |
c13182ef | 67 | This function is automatically called by the |
5b0dc1ba | 68 | other time conversion functions that depend on the timezone. |
464ba7fc | 69 | In a System-V-like environment, it will also set the variables \fItimezone\fP |
750d65df | 70 | (seconds West of UTC) and \fIdaylight\fP (to 0 if this timezone does not |
464ba7fc | 71 | have any daylight saving time rules, or to nonzero if there is a time during |
e2905dc1 | 72 | the year when daylight saving time applies). |
fea681da | 73 | .PP |
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74 | If the |
75 | .B TZ | |
76 | variable does not appear in the environment, the \fItzname\fP | |
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77 | variable is initialized with the best approximation of local wall clock |
78 | time, as specified by the | |
79 | .BR tzfile (5)-format | |
80 | file \fIlocaltime\fP | |
81 | found in the system timezone directory (see below). | |
82 | (One also often sees | |
83 | .I /etc/localtime | |
84 | used here, a symlink to the right file in the system timezone directory.) | |
85 | .PP | |
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86 | If the |
87 | .B TZ | |
88 | variable does appear in the environment but its value is empty | |
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89 | or its value cannot be interpreted using any of the formats specified |
90 | below, Coordinated Universal Time (UTC) is used. | |
91 | .PP | |
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92 | The value of |
93 | .B TZ | |
94 | can be one of three formats. | |
c13182ef | 95 | The first format is used |
5b0dc1ba | 96 | when there is no daylight saving time in the local timezone: |
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97 | .sp |
98 | .RS | |
99 | .I std offset | |
100 | .RE | |
101 | .sp | |
5b0dc1ba | 102 | The \fIstd\fP string specifies the name of the timezone and must be |
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103 | three or more alphabetic characters. |
104 | The \fIoffset\fP string immediately | |
fea681da | 105 | follows \fIstd\fP and specifies the time value to be added to the local |
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106 | time to get Coordinated Universal Time (UTC). |
107 | The \fIoffset\fP is positive | |
5b0dc1ba | 108 | if the local timezone is west of the Prime Meridian and negative if it is |
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109 | east. |
110 | The hour must be between 0 and 24, and the minutes and seconds | |
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111 | 0 and 59. |
112 | .PP | |
113 | The second format is used when there is daylight saving time: | |
114 | .sp | |
115 | .RS | |
116 | .I std offset dst [offset],start[/time],end[/time] | |
117 | .RE | |
118 | .sp | |
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119 | There are no spaces in the specification. |
120 | The initial \fIstd\fP and | |
5b0dc1ba | 121 | \fIoffset\fP specify the standard timezone, as described above. |
c13182ef | 122 | The \fIdst\fP string and \fIoffset\fP specify the name and offset for the |
5b0dc1ba | 123 | corresponding daylight saving timezone. |
c13182ef | 124 | If the offset is omitted, |
e2905dc1 | 125 | it default to one hour ahead of standard time. |
fea681da | 126 | .PP |
e2905dc1 | 127 | The \fIstart\fP field specifies when daylight saving time goes into |
fea681da | 128 | effect and the \fIend\fP field specifies when the change is made back to |
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129 | standard time. |
130 | These fields may have the following formats: | |
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131 | .TP |
132 | J\fIn\fP | |
c13182ef | 133 | This specifies the Julian day with \fIn\fP between 1 and 365. |
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134 | Leap days are not counted. |
135 | In this format, February 29 can't be represented; | |
136 | February 28 is day 59, and March 1 is always day 60. | |
c13182ef | 137 | .TP |
fea681da | 138 | .I n |
567e764a | 139 | This specifies the zero-based Julian day with \fIn\fP between 0 and 365. |
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140 | February 29 is counted in leap years. |
141 | .TP | |
fea681da | 142 | M\fIm\fP.\fIw\fP.\fId\fP |
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143 | This specifies day \fId\fP (0 <= \fId\fP <= 6) of week \fIw\fP |
144 | (1 <= \fIw\fP <= 5) of month \fIm\fP (1 <= \fIm\fP <= 12). | |
145 | Week 1 is | |
146 | the first week in which day \fId\fP occurs and week 5 is the last week | |
147 | in which day \fId\fP occurs. | |
148 | Day 0 is a Sunday. | |
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149 | .PP |
150 | The \fItime\fP fields specify when, in the local time currently in effect, | |
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151 | the change to the other time occurs. |
152 | If omitted, the default is 02:00:00. | |
e2905dc1 | 153 | |
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154 | Here is an example for New Zealand, |
155 | where the standard time (NZST) is 12 hours ahead of UTC, | |
156 | and daylight saving time (NZDT), 13 hours ahead of UTC, | |
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157 | runs from the first Sunday in October to the third Sunday in March, |
158 | and the changeovers happen at the default time of 02:00:00: | |
159 | .nf | |
160 | ||
4b9999d6 | 161 | TZ="NZST-12:00:00NZDT-13:00:00,M10.1.0,M3.3.0" |
e2905dc1 | 162 | .fi |
fea681da | 163 | .PP |
5b0dc1ba | 164 | The third format specifies that the timezone information should be read |
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165 | from a file: |
166 | .sp | |
167 | .RS | |
168 | :[filespec] | |
169 | .RE | |
170 | .sp | |
5b0dc1ba | 171 | If the file specification \fIfilespec\fP is omitted, the timezone |
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172 | information is read from the file |
173 | .I localtime | |
174 | in the system timezone directory, which nowadays usually is | |
175 | .IR /usr/share/zoneinfo . | |
176 | This file is in | |
177 | .BR tzfile (5) | |
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178 | format. |
179 | If \fIfilespec\fP is given, it specifies another | |
fea681da | 180 | .BR tzfile (5)-format |
5b0dc1ba | 181 | file to read the timezone information from. |
f81fb444 | 182 | If \fIfilespec\fP does not begin with a \(aq/\(aq, the file specification is |
fea681da | 183 | relative to the system timezone directory. |
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184 | .PP |
185 | Here's an example, once more for New Zealand: | |
186 | .nf | |
187 | ||
188 | TZ=":Pacific/Auckland" | |
189 | .fi | |
fea681da | 190 | .SH FILES |
5b0dc1ba | 191 | The system timezone directory used depends on the (g)libc version. |
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192 | Libc4 and libc5 use |
193 | .IR /usr/lib/zoneinfo , | |
194 | and, since libc-5.4.6, | |
195 | when this doesn't work, will try | |
196 | .IR /usr/share/zoneinfo . | |
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197 | Glibc2 will use the environment variable |
198 | .BR TZDIR , | |
199 | when that exists. | |
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200 | Its default depends on how it was installed, but normally is |
201 | .IR /usr/share/zoneinfo . | |
202 | .LP | |
203 | This timezone directory contains the files | |
204 | .nf | |
5b0dc1ba | 205 | localtime local timezone file |
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206 | posixrules rules for POSIX-style TZ's |
207 | .fi | |
208 | .LP | |
209 | Often | |
210 | .I /etc/localtime | |
211 | is a symlink to the file | |
212 | .I localtime | |
5b0dc1ba | 213 | or to the correct timezone file in the system timezone directory. |
fea681da | 214 | .SH "CONFORMING TO" |
44a2c328 | 215 | SVr4, POSIX.1-2001, 4.3BSD. |
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216 | .SH NOTES |
217 | Note that the variable \fIdaylight\fP does not indicate that daylight | |
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218 | saving time applies right now. |
219 | It used to give the number of some | |
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220 | algorithm (see the variable \fItz_dsttime\fP in |
221 | .BR gettimeofday (2)). | |
222 | It has been obsolete for many years but is required by SUSv2. | |
223 | .LP | |
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224 | 4.3BSD had a function |
225 | .BI "char *timezone(" zone ", " dst ) | |
226 | that returned the | |
5b0dc1ba | 227 | name of the timezone corresponding to its first argument (minutes |
750d65df | 228 | West of UTC). |
c13182ef | 229 | If the second argument was 0, the standard name was used, |
e2905dc1 | 230 | otherwise the daylight saving time version. |
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231 | .SH "SEE ALSO" |
232 | .BR date (1), | |
233 | .BR gettimeofday (2), | |
234 | .BR time (2), | |
235 | .BR ctime (3), | |
236 | .BR getenv (3), | |
237 | .BR tzfile (5) |