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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 <sys/time.h>

     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 incrementing it more slowly than normal until the correction is complete.  If delta is posi-tive, positive,
     tive, 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 correction
     tion from an earlier call to adjtime() may not be finished when adjtime() is called again.  If olddelta
     is non-nil, the structure pointed to will contain, upon return, the number of microseconds still to be
     corrected from the earlier call.

     This call may be used by time servers that synchronize the clocks of computers 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.

     The call adjtime() is restricted to the super-user.

RETURN VALUES
     A return value of 0 indicates that the call succeeded.  A return value of -1 indicates that an error
     occurred, and in this case an error code is stored in the global variable errno.

ERRORS
     Adjtime() will fail if:

     [EFAULT]           An argument points outside the process's allocated address space.

     [EPERM]            The process's effective user ID is not that of the super-user.

SEE ALSO
     date(1), gettimeofday(2), timed(8), timedc(8)

     R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX 4.3BSD.

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

4.3 Berkeley Distribution        June 4, 1993        4.3 Berkeley Distribution