ADJTIME(2)                FreeBSD System Calls Manual               ADJTIME(2)

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

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/time.h>

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

DESCRIPTION
     The adjtime() system call 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 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 correction from an earlier call to adjtime()
     may not be finished when adjtime() is called again.  If olddelta is not a
     null pointer, 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 adjtime() system call is restricted to the super-user.

RETURN VALUES
     The adjtime() function returns the value 0 if successful; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     The adjtime() system call 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() system call appeared in 4.3BSD.

FreeBSD 13.1-RELEASE-p6          June 4, 1993          FreeBSD 13.1-RELEASE-p6