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

NAME
     gettimeofday, settimeofday -- get/set date and time

SYNOPSIS
     #include <&lt;sys/time.h>&gt;

     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() call, and set with the
     settimeofday() 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 continuously 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 since Jan. 1, 1970 */
             suseconds_t     tv_usec;        /* and microseconds */
     };

     struct timezone {
             int     tz_minuteswest; /* of Greenwich */
             int     tz_dsttime;     /* type of dst correction to apply */
     };

     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 superuser may set the time of day or time zone.  If the system
     securelevel is greater than 1 (see init(8)), the time may only be
     advanced.  This limitation is imposed to prevent a malicious superuser
     from setting arbitrary time stamps on files.  The system time can still
     be adjusted backwards using the adjtime(2) system call even when the sys-
     tem 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
     gettimeofday() and settimeofday() will succeed unless:

     [EFAULT]           An argument address referenced invalid memory.

     In addition, settimeofday() may return the following error:

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

SEE ALSO
     date(1), adjtime(2), clock_gettime(2), getitimer(2), ctime(3), time(3)

STANDARDS
     The gettimeofday() function conforms to IEEE Std 1003.1-2008
     (``POSIX.1'').

HISTORY
     As predecessors of these functions, former system calls time() and
     stime() first appeared in Version 1 AT&T UNIX, and ftime() first appeared
     in Version 7 AT&T UNIX.  The gettimeofday() and settimeofday() system
     calls first appeared in 4.1cBSD.

CAVEATS
     Setting the time with settimeofday() is dangerous; if possible use
     adjtime(2) instead.  Many daemon programming techniques utilize time-
     delta techniques using the results from gettimeofday() instead of from
     clock_gettime(2) on the CLOCK_MONOTONIC clock.  Time jumps can cause
     these programs to malfunction in unexpected ways.  If the time must be
     set, consider rebooting the machine for safety.

BSD                            December 10, 2014                           BSD