bsd/man/man2/gettimeofday.2

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  34 .\"     @(#)gettimeofday.2      8.2 (Berkeley) 5/26/95
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  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 .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 .Bf -symbolic
  57 Note: timezone is no longer used; this information is kept outside
  58 the kernel.
  59 .Ef
  60 .Pp
  61 The system's notion of the current Greenwich time and the current time
  62 zone is obtained with the
  63 .Fn gettimeofday
  64 call, and set with the
  65 .Fn settimeofday
  66 call.  The time is expressed in seconds and microseconds
  67 since midnight (0 hour), January 1, 1970.  The resolution of the system
  68 clock is hardware dependent, and the time may be updated continuously or
  69 in ``ticks.''  If
  70 .Fa tp
  71 or
  72 .Fa tzp
  73 is NULL, the associated time
  74 information will not be returned or set.
  75 .Pp
  76 The structures pointed to by
  77 .Fa tp
  78 and
  79 .Fa tzp
  80 are defined in
  81 .Ao Pa sys/time.h Ac
  82 as:
  83 .Pp
  84 .Bd -literal
  85 struct timeval {
  86         time_t       tv_sec;   /* seconds since Jan. 1, 1970 */
  87         suseconds_t  tv_usec;  /* and microseconds */
  88 };
  89
  90 struct timezone {
  91         int     tz_minuteswest; /* of Greenwich */
  92         int     tz_dsttime;     /* type of dst correction to apply */
  93 };
  94 .Ed
  95 .Pp
  96 The
  97 .Fa timeval
  98 structure specifies a time value in seconds and microseconds.
  99 The values in
 100 .Fa timeval
 101 are opaque types whose length may vary on different machines;
 102 depending on them to have any given length may lead to errors.
 103 .Pp
 104 The
 105 .Fa timezone
 106 structure indicates the local time zone
 107 (measured in minutes of time westward from Greenwich),
 108 and a flag that, if nonzero, indicates that
 109 Daylight Saving time applies locally during
 110 the appropriate part of the year.
 111 .Pp
 112 Only the super-user may set the time of day or time zone.
 113 If the system securelevel is greater than 1 (see
 114 .Xr init 8 ),
 115 the time may only be advanced.
 116 This limitation is imposed to prevent a malicious super-user
 117 from setting arbitrary time stamps on files.
 118 The system time can still be adjusted backwards using the
 119 .Xr adjtime 2
 120 system call even when the system is secure.
 121 .Sh RETURN
 122 A 0 return value indicates that the call succeeded.
 123 A -1 return value indicates an error occurred, and in this
 124 case an error code is stored into the global variable
 125 .Va errno .
 126 .Sh ERRORS
 127 The following error codes may be set in
 128 .Va errno :
 129 .Bl -tag -width [EFAULT]
 130 .It Bq Er EFAULT
 131 An argument address referenced invalid memory.
 132 .It Bq Er EPERM
 133 A user other than the super-user attempted to set the time.
 134 .El
 135 .Sh LEGACY SYNOPSIS
 136 .Fd #include <sys/time.h>
 137 .Pp
 138 .Ft int
 139 .br
 140 .Fo gettimeofday
 141 .Fa "struct timeval *tp"
 142 .Fa "struct timezone *tzp"
 143 .Fc ;
 144 .Pp
 145 The type of
 146 .Fa tzp
 147 has changed.
 148 .Sh SEE ALSO
 149 .Xr date 1 ,
 150 .Xr adjtime 2 ,
 151 .Xr ctime 3 ,
 152 .Xr compat 5 ,
 153 .Xr timed 8
 154 .Sh HISTORY
 155 The
 156 .Fn gettimeofday
 157 function call appeared in
 158 .Bx 4.2 .