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ADJTIME(2)                    System Calls Manual                   ADJTIME(2)



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

SYNOPSIS
       #include <&lt;sys/time.h>&gt;

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

DESCRIPTION
       adjtime()  adjusts the system's notion of the current time, as returned
       by gettimeofday(2), advancing or retarding it by  the  amount  of  time
       specified in the struct timeval (defined in <&lt;sys/time.h>&gt;) pointed to by
       delta.

       The adjustment is effected by speeding up (if that amount  of  time  is
       positive) or slowing down (if that amount of time is negative) the sys-
       tem's clock by some small percentage, generally a fraction of one  per-
       cent.  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,
       then the structure it points to will contain, upon return,  the  number
       of  microseconds  still to be corrected from the earlier call.  If old-
       delta is a NULL pointer, the  corresponding  information  will  not  be
       returned.

       This  call  may  be used in 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.

       Only the super-user may adjust the time of day.

       The adjustment value will be silently rounded to the resolution of  the
       system clock.

RETURN
       A  0 return value indicates that the call succeeded.  A -1 return value
       indicates an error occurred, and in this case an error code  is  stored
       into the global variable errno.

ERRORS
       EFAULT         delta or olddelta points outside the process's allocated
                      address space.

                      olddelta points to a region of  the  process'  allocated
                      address space that is not writable.

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

SEE ALSO
       date(1V), gettimeofday(2)



                                21 January 1990                     ADJTIME(2)