1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
|
.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" Modified by Michael Haardt (michael@moria.de)
.\" Modified 1993-07-23 by Rik Faith (faith@cs.unc.edu)
.\" Modified 1994-08-21 by Michael Chastain (mec@shell.portal.com):
.\" Fixed necessary '#include' lines.
.\" Modified 1995-04-15 by Michael Chastain (mec@shell.portal.com):
.\" Added reference to adjtimex.
.\" Removed some nonsense lines pointed out by Urs Thuermann,
.\" (urs@isnogud.escape.de), aeb, 950722.
.\" Modified 1997-01-14 by Austin Donnelly (and1000@debian.org):
.\" Added return values section, and bit on EFAULT
.\" Added clarification on timezone, aeb, 971210.
.\" Removed "#include <unistd.h>", aeb, 010316.
.\" Modified, 2004-05-27 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" Added notes on capability requirement.
.\"
.TH GETTIMEOFDAY 2 2012-04-26 "Linux" "Linux Programmer's Manual"
.SH NAME
gettimeofday, settimeofday \- get / set time
.SH SYNOPSIS
.nf
.B #include <sys/time.h>
.BI "int gettimeofday(struct timeval *" tv ", struct timezone *" tz );
.BI "int settimeofday(const struct timeval *" tv \
", const struct timezone *" tz );
.fi
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR settimeofday ():
_BSD_SOURCE
.SH DESCRIPTION
The functions
.BR gettimeofday ()
and
.BR settimeofday ()
can get and set the time as well as a timezone.
The
.I tv
argument is a
.I struct timeval
(as specified in
.IR <sys/time.h> ):
.sp
.in +4n
.nf
struct timeval {
time_t tv_sec; /* seconds */
suseconds_t tv_usec; /* microseconds */
};
.fi
.in
.sp
and gives the number of seconds and microseconds since the Epoch (see
.BR time (2)).
The
.I tz
argument is a
.IR "struct timezone" :
.sp
.in +4n
.nf
struct timezone {
int tz_minuteswest; /* minutes west of Greenwich */
int tz_dsttime; /* type of DST correction */
};
.fi
.in
.PP
If either
.I tv
or
.I tz
is NULL, the corresponding structure is not set or returned.
.\" FIXME The compilation warning looks to be going away in 2.17
.\" see glibc commit 4b7634a5e03b0da6f8875de9d3f74c1cf6f2a6e8
(However, compilation warnings will result if
.I tv
is NULL.)
.\" The following is covered under EPERM below:
.\" .PP
.\" Only the superuser may use
.\" .BR settimeofday ().
.PP
The use of the
.I timezone
structure is obsolete; the
.I tz
argument should normally be specified as NULL.
(See NOTES below.)
Under Linux, there are some peculiar "warp clock" semantics associated
with the
.BR settimeofday ()
system call if on the very first call (after booting)
that has a non-NULL
.I tz
argument, the
.I tv
argument is NULL and the
.I tz_minuteswest
field is nonzero.
(The
.I tz_dsttime
field should be zero for this case.)
In such a case it is assumed that the CMOS clock
is on local time, and that it has to be incremented by this amount
to get UTC system time.
No doubt it is a bad idea to use this feature.
.SH RETURN VALUE
.BR gettimeofday ()
and
.BR settimeofday ()
return 0 for success, or \-1 for failure (in which case
.I errno
is set appropriately).
.SH ERRORS
.TP
.B EFAULT
One of
.I tv
or
.I tz
pointed outside the accessible address space.
.TP
.B EINVAL
Timezone (or something else) is invalid.
.TP
.B EPERM
The calling process has insufficient privilege to call
.BR settimeofday ();
under Linux the
.B CAP_SYS_TIME
capability is required.
.SH CONFORMING TO
SVr4, 4.3BSD.
POSIX.1-2001 describes
.BR gettimeofday ()
but not
.BR settimeofday ().
POSIX.1-2008 marks
.BR gettimeofday ()
as obsolete, recommending the use of
.BR clock_gettime (2)
instead.
.SH NOTES
The time returned by
.BR gettimeofday ()
.I is
affected by discontinuous jumps in the system time
(e.g., if the system administrator manually changes the system time).
If you need a monotonically increasing clock, see
.BR clock_gettime (2).
Macros for operating on
.I timeval
structures are described in
.BR timeradd (3).
Traditionally, the fields of
.I struct timeval
were of type
.IR long .
The
.I tz_dsttime
field has never been used under Linux.
.\" it has not
.\" been and will not be supported by libc or glibc.
.\" Each and every occurrence of this field in the kernel source
.\" (other than the declaration) is a bug.
Thus, the following
is purely of historic interest.
On old systems, the field
.I tz_dsttime
contains a symbolic constant (values are given below)
that indicates in which part of the year Daylight Saving Time
is in force.
(Note: this value is constant throughout the year:
it does not indicate that DST is in force, it just selects an
algorithm.)
The daylight saving time algorithms defined are as follows:
.in +4n
.nf
\fBDST_NONE\fP /* not on DST */
.br
\fBDST_USA\fP /* USA style DST */
.br
\fBDST_AUST\fP /* Australian style DST */
.br
\fBDST_WET\fP /* Western European DST */
.br
\fBDST_MET\fP /* Middle European DST */
.br
\fBDST_EET\fP /* Eastern European DST */
.br
\fBDST_CAN\fP /* Canada */
.br
\fBDST_GB\fP /* Great Britain and Eire */
.br
\fBDST_RUM\fP /* Romania */
.br
\fBDST_TUR\fP /* Turkey */
.br
\fBDST_AUSTALT\fP /* Australian style with shift in 1986 */
.fi
.in
.PP
Of course it turned out that the period in which
Daylight Saving Time is in force cannot be given
by a simple algorithm, one per country; indeed,
this period is determined by unpredictable political
decisions.
So this method of representing timezones
has been abandoned.
.SH SEE ALSO
.BR date (1),
.BR adjtimex (2),
.BR clock_gettime (2),
.BR time (2),
.BR ctime (3),
.BR ftime (3),
.BR timeradd (3),
.BR capabilities (7),
.BR time (7)
|
