bsd/man/man2/gettimeofday.2

   1 .\"     $OpenBSD: gettimeofday.2,v 1.5 1997/03/16 01:18:49 flipk Exp $
   2 .\"
   3 .\" Copyright (c) 1980, 1991, 1993
   4 .\"     The Regents of the University of California.  All rights reserved.
   5 .\"
   6 .\" Redistribution and use in source and binary forms, with or without
   7 .\" modification, are permitted provided that the following conditions
   8 .\" are met:
   9 .\" 1. Redistributions of source code must retain the above copyright
  10 .\"    notice, this list of conditions and the following disclaimer.
  11 .\" 2. Redistributions in binary form must reproduce the above copyright
  12 .\"    notice, this list of conditions and the following disclaimer in the
  13 .\"    documentation and/or other materials provided with the distribution.
  14 .\" 3. All advertising materials mentioning features or use of this software
  15 .\"    must display the following acknowledgement:
  16 .\"     This product includes software developed by the University of
  17 .\"     California, Berkeley and its contributors.
  18 .\" 4. Neither the name of the University nor the names of its contributors
  19 .\"    may be used to endorse or promote products derived from this software
  20 .\"    without specific prior written permission.
  21 .\"
  22 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32 .\" SUCH DAMAGE.
  33 .\"
  34 .\"     @(#)gettimeofday.2      8.2 (Berkeley) 5/26/95
  35 .\"
  36 .Dd May 26, 1995
  37 .Dt GETTIMEOFDAY 2
  38 .Os BSD 4
  39 .Sh NAME
  40 .Nm gettimeofday ,
  41 .Nm settimeofday
  42 .Nd get/set date and time
  43 .Sh SYNOPSIS
  44 .Fd #include <sys/time.h>
  45 .Ft int
  46 .Fn gettimeofday "struct timeval *tp" "struct timezone *tzp"
  47 .Ft int
  48 .Fn settimeofday "const struct timeval *tp" "const struct timezone *tzp"
  49 .Sh DESCRIPTION
  50 .Bf -symbolic
  51 Note: timezone is no longer used; this information is kept outside
  52 the kernel.
  53 .Ef
  54 .Pp
  55 The system's notion of the current Greenwich time and the current time
  56 zone is obtained with the
  57 .Fn gettimeofday
  58 call, and set with the
  59 .Fn settimeofday
  60 call.  The time is expressed in seconds and microseconds
  61 since midnight (0 hour), January 1, 1970.  The resolution of the system
  62 clock is hardware dependent, and the time may be updated continuously or
  63 in ``ticks.''  If
  64 .Fa tp
  65 or
  66 .Fa tzp
  67 is NULL, the associated time
  68 information will not be returned or set.
  69 .Pp
  70 The structures pointed to by
  71 .Fa tp
  72 and
  73 .Fa tzp
  74 are defined in
  75 .Ao Pa sys/time.h Ac
  76 as:
  77 .Pp
  78 .Bd -literal
  79 struct timeval {
  80         long    tv_sec;         /* seconds since Jan. 1, 1970 */
  81         long    tv_usec;        /* and microseconds */
  82 };
  83
  84 struct timezone {
  85         int     tz_minuteswest; /* of Greenwich */
  86         int     tz_dsttime;     /* type of dst correction to apply */
  87 };
  88 .Ed
  89 .Pp
  90 The
  91 .Fa timezone
  92 structure indicates the local time zone
  93 (measured in minutes of time westward from Greenwich),
  94 and a flag that, if nonzero, indicates that
  95 Daylight Saving time applies locally during
  96 the appropriate part of the year.
  97 .Pp
  98 Only the super-user may set the time of day or time zone.
  99 If the system securelevel is greater than 1 (see
 100 .Xr init 8 ),
 101 the time may only be advanced.
 102 This limitation is imposed to prevent a malicious super-user
 103 from setting arbitrary time stamps on files.
 104 The system time can still be adjusted backwards using the
 105 .Xr adjtime 2
 106 system call even when the system is secure.
 107 .Sh RETURN
 108 A 0 return value indicates that the call succeeded.
 109 A -1 return value indicates an error occurred, and in this
 110 case an error code is stored into the global variable
 111 .Va errno .
 112 .Sh ERRORS
 113 The following error codes may be set in
 114 .Va errno :
 115 .Bl -tag -width [EFAULT]
 116 .It Bq Er EFAULT
 117 An argument address referenced invalid memory.
 118 .It Bq Er EPERM
 119 A user other than the super-user attempted to set the time.
 120 .El
 121 .Sh SEE ALSO
 122 .Xr date 1 ,
 123 .Xr adjtime 2 ,
 124 .Xr ctime 3 ,
 125 .Xr timed 8
 126 .Sh HISTORY
 127 The
 128 .Fn gettimeofday
 129 function call appeared in
 130 .Bx 4.2 .