adjtime(2) - NetBSD Manual Pages

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ADJTIME(2)                NetBSD 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

     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 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 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.

     If the calling user is not the super user, the adjtime() system call will
     fail, and the adjtime() function in the standard C library will try to
     use the clockctl(4) device if present, thus making it possible for non
     privileged users to adjust the system time.  If clockctl(4) is not
     present or not accessible, then adjtime() returns EPERM.


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), clockctl(4), 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.

NetBSD 10.1                    December 8, 2015                    NetBSD 10.1