settimeofday man page on FreeBSD

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GETTIMEOFDAY(2)		    BSD System Calls Manual	       GETTIMEOFDAY(2)

NAME
     gettimeofday, settimeofday — get/set date and time

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/time.h>

     int
     gettimeofday(struct timeval *tp, struct timezone *tzp);

     int
     settimeofday(const struct timeval *tp, const struct timezone *tzp);

DESCRIPTION
     Note: timezone is no longer used; this information is kept outside the
     kernel.

     The system's notion of the current Greenwich time and the current time
     zone is obtained with the gettimeofday() system call, and set with the
     settimeofday() system call.  The time is expressed in seconds and
     microseconds since midnight (0 hour), January 1, 1970.  The resolution of
     the system clock is hardware dependent, and the time may be updated con‐
     tinuously or in “ticks”.  If tp or tzp is NULL, the associated time
     information will not be returned or set.

     The structures pointed to by tp and tzp are defined in <sys/time.h> as:

     struct timeval {
	     time_t	     tv_sec;	     /* seconds */
	     suseconds_t     tv_usec;	     /* and microseconds */
     };

     struct timezone {
	     int     tz_minuteswest; /* minutes west of Greenwich */
	     int     tz_dsttime;     /* type of dst correction */
     };

     The timezone structure indicates the local time zone (measured in minutes
     of time westward from Greenwich), and a flag that, if nonzero, indicates
     that Daylight Saving time applies locally during the appropriate part of
     the year.

     Only the super-user may set the time of day or time zone.	If the system
     is running at securelevel >= 2 (see init(8)), the time may only be
     advanced or retarded by a maximum of one second.  This limitation is
     imposed to prevent a malicious super-user from setting arbitrary time
     stamps on files.  The system time can be adjusted backwards without
     restriction using the adjtime(2) system call even when the system is
     secure.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     The following error codes may be set in errno:

     [EFAULT]		An argument address referenced invalid memory.

     [EPERM]		A user other than the super-user attempted to set the
			time.

SEE ALSO
     date(1), adjtime(2), clock_gettime(2), ctime(3), timeradd(3), clocks(7),
     timed(8)

HISTORY
     The gettimeofday() system call appeared in 4.2BSD.

BSD				 May 26, 1995				   BSD
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