Penguin
Recent Changes
Annotated edit history of tzset(3) version 1, including all changes. View license author blame.
Rev Author # Line
1 perry 1 TZSET
2 !!!TZSET
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 FILES
7 CONFORMING TO
8 SEE ALSO
9 ----
10 !!NAME
11
12
13 tzset - initialize time conversion information
14 !!SYNOPSIS
15
16
17 __#include
18 __''tzname''__[[2]
19 __
20 !!DESCRIPTION
21
22
23 The __tzset()__ function initializes the ''tzname''
24 variable from the TZ environment variable. This function is
25 automatically called by the other time conversion functions
26 that depend on the time zone.
27
28
29 If the TZ variable does not appear in the environment, the
30 ''tzname'' variable is initialized with the best
31 approximation of local wall clock time, as specified by the
32 tzfile(5)-format file ''localtime'' found in the
33 system timezone directory (see below). (One also often sees
34 ''/etc/localtime'' used here, a symlink to the right file
35 in the system timezone directory.)
36
37
38 If the TZ variable does appear in the environment but its
39 value is NULL or its value cannot be interpreted using any
40 of the formats specified below, Coordinated Universal Time
41 (UTC) is used.
42
43
44 The value of TZ can be one of three formats. The first
45 format is used when there is no daylight saving time in the
46 local time zone:
47
48
49 ''std offset''
50
51
52 The ''std'' string specifies the name of the time zone
53 and must be three or more alphabetic characters. The
54 ''offset'' string immediately follows ''std'' and
55 specifies the time value to be added to the local time to
56 get Coordinated Universal Time (UTC). The ''offset'' is
57 positive if the local time zone is west of the Prime
58 Meridian and negative if it is east. The hour must be
59 between 0 and 24, and the minutes and seconds 0 and
60 59.
61
62
63 The second format is used when there is daylight saving
64 time:
65
66
67 ''std offset dst
68 [[offset],start[[/time],end[[/time]''
69
70
71 There are no spaces in the specification. The initial
72 ''std'' and ''offset'' specify the standard time zone,
73 as described above. The ''dst'' string and ''offset''
74 specify the name and offset for the corresponding daylight
75 savings time zone. If the offset is omitted, it defaults to
76 one hour ahead of standard time.
77
78
79 The ''start'' field specifies when daylight savings time
80 goes into effect and the ''end'' field specifies when the
81 change is made back to standard time. These fields may have
82 the following formats:
83
84
85 J''n''
86
87
88 This specifies the Julian day with ''n'' between 1 and
89 365. February 29 is never counted even in leap
90 years.
91
92
93 ''n''
94
95
96 This specifies the Julian day with ''n'' between 1 and
97 365. February 29 is counted in leap years.
98
99
100 M''m''.''w''.''d''
101
102
103 This specifies day ''d'' (0 ''d''
104 ''w'' (1 ''w'' ''m''
105 (1 ''m''
106 ''d'' occurs and week 5 is the last week in
107 which day ''d'' occurs. Day 0 is a Sunday.
108
109
110 The ''time'' fields specify when, in the local time
111 currently in effect, the change to the other time occurs. If
112 omitted, the default is 02:00:00.
113
114
115 The third format specifies that the time zone information
116 should be read from a file:
117
118
119 :[[filespec]
120
121
122 If the file specification ''filespec'' is omitted, the
123 time zone information is read from the file ''localtime''
124 in the system timezone directory, which nowadays usually is
125 ''/usr/share/zoneinfo''. This file is in tzfile(5)
126 format. If ''filespec'' is given, it specifies another
127 tzfile(5)-format file to read the time zone
128 information from. If ''filespec'' does not begin with a
129 `/', the file specification is relative to the system
130 timezone directory.
131 !!FILES
132
133
134 The system time zone directory used depends on the (g)libc
135 version. Libc4 and libc5 use ''/usr/lib/zoneinfo'', and,
136 since libc-5.4.6, when this doesn't work, will try
137 ''/usr/share/zoneinfo''. Glibc2 will use the environment
138 variable TZDIR, when that exists. Its default depends on how
139 it was installed, but normally is
140 ''/usr/share/zoneinfo''.
141
142
143 This timezone directory contains the files
144
145
146 localtime local time zone file
147 posixrules rules for POSIX-style TZ's
148 Often ''/etc/localtime'' is a symlink to the file ''localtime'' or to the correct time zone file in the system time zone directory.
149 !!CONFORMING TO
150
151
152 SVID 3, POSIX, BSD 4.3
153 !!SEE ALSO
154
155
156 date(1), gettimeofday(2), time(2),
157 ctime(3), getenv(3),
158 tzfile(5)
159 ----
This page is a man page (or other imported legacy content). We are unable to automatically determine the license status of this page.