NAME    [Toc]    [Back]

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

LIBRARY    [Toc]    [Back]

     Standard C Library (libc, -lc)

SYNOPSIS    [Toc]    [Back]

     #include <sys/time.h>

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

DESCRIPTION    [Toc]    [Back]

     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 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 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.

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

RETURN VALUES    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

     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    [Toc]    [Back]

     The adjtime() function call appeared in 4.3BSD.

BSD                              June 4, 1993                              BSD