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