bsd/man/man2/gettimeofday.2

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  34 .\"     @(#)gettimeofday.2      8.2 (Berkeley) 5/26/95
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  36 .Dd August 5, 2008
  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 .Fo gettimeofday
  47 .Fa "struct timeval *restrict tp"
  48 .Fa "void *restrict tzp"
  49 .Fc
  50 .Ft int
  51 .Fo settimeofday
  52 .Fa "const struct timeval *tp"
  53 .Fa "const struct timezone *tzp"
  54 .Fc
  55 .Sh DESCRIPTION
  56 .Pp
  57 The system's notion of the current Greenwich time and the current time
  58 zone is obtained with the
  59 .Fn gettimeofday
  60 call, and set with the
  61 .Fn settimeofday
  62 call.  The time is expressed in seconds and microseconds
  63 since midnight (0 hour), January 1, 1970.  The resolution of the system
  64 clock is hardware dependent, and the time may be updated continuously or
  65 in ``ticks.''  If
  66 .Fa tp
  67 is NULL
  68 and
  69 .Fa tzp
  70 is non-NULL,
  71 .Fn gettimeofday
  72 will populate the timezone struct in
  73 .Fa tzp .
  74 If
  75 .Fa tp
  76 is non-NULL and
  77 .Fa tzp
  78 is NULL, then only the timeval struct in
  79 .Fa tp
  80 is populated. If both
  81 .Fa tp
  82 and
  83 .Fa tzp
  84 are NULL, nothing is returned.
  85 .Pp
  86 The structures pointed to by
  87 .Fa tp
  88 and
  89 .Fa tzp
  90 are defined in
  91 .Ao Pa sys/time.h Ac
  92 as:
  93 .Pp
  94 .Bd -literal
  95
  96 struct timeval {
  97         time_t       tv_sec;   /* seconds since Jan. 1, 1970 */
  98         suseconds_t  tv_usec;  /* and microseconds */
  99 };
 100
 101 struct timezone {
 102         int     tz_minuteswest; /* of Greenwich */
 103         int     tz_dsttime;     /* type of dst correction to apply */
 104 };
 105
 106 .Ed
 107 .Pp
 108 The
 109 .Fa timeval
 110 structure specifies a time value in seconds and microseconds.
 111 The values in
 112 .Fa timeval
 113 are opaque types whose length may vary on different machines;
 114 depending on them to have any given length may lead to errors.
 115 .Pp
 116 The
 117 .Fa timezone
 118 structure indicates the local time zone
 119 (measured in minutes of time westward from Greenwich),
 120 and a flag that, if nonzero, indicates that
 121 Daylight Saving time applies locally during
 122 the appropriate part of the year.
 123 .Pp
 124 Only the super-user may set the time of day or time zone.
 125 If the system securelevel is greater than 1 (see
 126 .Xr init 8 ),
 127 the time may only be advanced.
 128 This limitation is imposed to prevent a malicious super-user
 129 from setting arbitrary time stamps on files.
 130 The system time can still be adjusted backwards using the
 131 .Xr adjtime 2
 132 system call even when the system is secure.
 133 .Sh RETURN
 134 A 0 return value indicates that the call succeeded.
 135 A -1 return value indicates an error occurred, and in this
 136 case an error code is stored into the global variable
 137 .Va errno .
 138 .Sh ERRORS
 139 The following error codes may be set in
 140 .Va errno :
 141 .Bl -tag -width [EFAULT]
 142 .It Bq Er EFAULT
 143 An argument address referenced invalid memory.
 144 .It Bq Er EPERM
 145 A user other than the super-user attempted to set the time.
 146 .El
 147 .Sh LEGACY SYNOPSIS
 148 .Fd #include <sys/time.h>
 149 .Pp
 150 .Ft int
 151 .br
 152 .Fo gettimeofday
 153 .Fa "struct timeval *tp"
 154 .Fa "struct timezone *tzp"
 155 .Fc ;
 156 .Pp
 157 The type of
 158 .Fa tzp
 159 has changed.
 160 .Sh SEE ALSO
 161 .Xr date 1 ,
 162 .Xr adjtime 2 ,
 163 .Xr ctime 3 ,
 164 .Xr compat 5 ,
 165 .Xr timed 8
 166 .Sh HISTORY
 167 The
 168 .Fn gettimeofday
 169 function call appeared in
 170 .Bx 4.2 .