ADJTIME(2)                           BSD                            ADJTIME(2)



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

SYNOPSIS
     #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(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.  If delta
     is NULL, the skew is zero, and the clock is not affected.

     A time correction from an earlier call to adjtime may not be finished
     when adjtime is called again.  If olddelta is nonzero, then 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(2) is restricted to the super-user.

ERRORS
     The following error codes may be set in errno:

     [EINVAL]   The absolute value of delta exceeds ADJTIME_MAX_DELTA (defined
                in <sys/time.h>).

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

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

DIAGNOSTICS
     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.

SEE ALSO
     date(1), gettimeofday(2)
     TSP: The Time Synchronization Protocol for UNIX 4.3BSD, R. Gusella and S.
     Zatti

NOTES
     adjtime affects the value Domain/OS uses to seed the algorithm by which
     it computes UIDs (unique identifiers).  The UID generator is seeded when
     the system is booted.  Using adjtime to set the time backwards,
     therefore, incurs the risk that objects created during the interval of
     time starting after the workstation is shut down and lasting for as long
     as the time was set backwards will be assigned the same UIDs as existing
     objects.  The only way to eliminate this risk entirely is not to create
     any objects during this time:  when shutting down, wait for as much time
     as the time was set backwards before rebooting.