adjtime(SSC)                   6 January 1993                   adjtime(SSC)


 Name

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

 Syntax


    #include <sys/time.h>

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


 Description

    adjtime makes adjustments to the system time, as returned by
    gettimeofday(SSC), advancing or retarding it by the time specified by the
    timeval delta.  If delta is negative, the clock is slowed down.  If delta
    is positive, the clock is set ahead.  The structure pointed to will con-
    tain, upon return, the number of microseconds still to be corrected from
    the earlier call.

    adjtime is intended for making adjustments in small increments; there-
    fore, the time adjustment specified by delta should be less than or equal
    to 20 seconds.

    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.

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

 Return value

    A return value of zero 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

    The following error codes may be set in errno:

    [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.

 Note

    Implementations with poor control over the system clock will always
    return a zero timeval for olddelta.

    The time adjustment to be made may be incorrectly calculated if the time
    adjustment specified by delta is greater than 20 seconds.

 See also

    date(C), gettimeofday(SSC), rdate(ADMN), timed(ADMN) and timedc(ADMN).