adjtime man page on DigitalUNIX

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adjtime(2)							    adjtime(2)

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

       #include <sys/time.h>

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

       Points  to  the	amount of time to be altered.  Points to the number of
       nanoseconds still to be corrected from an earlier call.

       The adjtime() function makes small adjustments to the system  time  (as
       returned by the gettimer() function), advancing or decreasing it by the
       time specified by the delta parameter  of  the  timeval	structure.  If
       delta  is  negative,  the  clock is slowed down by incrementing it more
       slowly than normal until the correction is complete. If delta is	 posi‐
       tive,  a	 larger	 increment than normal is used until the correction is

       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. In this case, the delta remaining  from
       the  original call is replaced by the delta of the current call. If the
       old_delta parameter  is	nonzero,  then	when  the  adjtime()  function
       returns,	 the structure pointed to will contain the time remaining 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 adjtime() function is restricted
       to users with the superuser privilege.

       In BSD, system time is defined in units of  seconds  and	 microseconds,
       while in POSIX real time extensions, the units are seconds and nanosec‐
       onds.  However, the adjtime()  function	is  not	 specified  by	POSIX.
       Therefore, the existing BSD interface is preserved.

       On  successful  completion, the adjtime() function returns 0 (zero). If
       the adjtime() function fails, it returns -1 and sets errno to  indicate
       the error.

       If the adjtime() function fails, errno may be set to one of the follow‐
       ing  values:  An	 argument  address  referenced	invalid	 memory.   The
       process's effective user ID does not have appropriate system privilege.

       Functions: gettimeofday(2), gettimer(3)


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