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ADJTIME(2)                  BSD System Calls Manual                 ADJTIME(2)

NAME
     adjtime -- correct the time to allow synchronization of the system clock

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

     int
     adjtime(const struct timeval *delta, struct timeval *olddelta);

DESCRIPTION
     adjtime() makes small adjustments to the system time, as returned by
     gettimeofday(2), advancing or retarding it by the time specified by the
     timeval delta.  If delta is negative, the clock is slowed down by incre-
     menting it more slowly than normal until the correction is complete.  If
     delta is positive, a larger increment than normal is used.  The skew used
     to perform the correction is generally a fraction of one percent.  Thus,
     the time is always a monotonically increasing function.  A time correc-
     tion from an earlier call to adjtime() may not be finished when adjtime()
     is called again.  If delta is null, no adjustment is done.  If olddelta
     is non-null, the structure pointed to will contain, upon return, the num-
     ber of microseconds still to be corrected from the earlier call.  Setting
     the time with settimeofday(2) will cancel any in-progress time adjust-
     ment.

     This call may be used by time servers that synchronize the clocks of com-
     puters in a local area network.  Such time servers would slow down the
     clocks of some machines and speed up the clocks of others to bring them
     to the average network time.

     Only the superuser may adjust the time using the adjtime() function.

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
     adjtime() will fail if:

     [EFAULT]           Either of the arguments point outside the process's
                        allocated address space.

     [EPERM]            The delta() argument is non-null and the process's
                        effective user ID is not that of the superuser.

SEE ALSO
     date(1), adjfreq(2), gettimeofday(2), ntpd(8)

HISTORY
     The adjtime() function call appeared in 4.3BSD.

CAVEATS
     Other operating systems restrict calling adjtime to the superuser and
     might not allow requesting the current correction without specifying a
     new value.

BSD                             April 29, 2017                             BSD