ADJTIME(2)	    UNIX Programmer's Manual	       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 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 nega-
     tive, 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 frac-
     tion of one percent.  Thus, the time is always a monotoni-
     cally increasing function.  A time correction from an ear-
     lier call to adjtime may not be finished when adjtime is
     called again.  If olddelta is non-zero, 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.

RETURN VALUE
     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
     The following error codes may be set in errno:

     [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), timed(8), timedc(8),
     TSP: The Time Synchronization Protocol for UNIX 4.3BSD, R.


Printed 11/26/99	  May 15, 1986				1


ADJTIME(2)	    UNIX Programmer's Manual	       ADJTIME(2)


     Gusella and S. Zatti

NOTES  (PDP-11)
     Adjtime(2) calls are executed immediately, not over a period
     of time, therefore, the olddelta return values for an adj-
     time(2) call will always be zero.


Printed 11/26/99	  May 15, 1986				2


 
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