adjtime(2)                                                          adjtime(2)


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

SYNOPSIS
     #include <sys/time.h>

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

DESCRIPTION
     adjtime adjusts the system's notion of the current time, as returned by
     gettimeofday(3C), advancing or retarding it by the amount of time
     specified in the struct timeval 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
     system's clock by some small percentage, 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 delta is 0, then olddelta returns the
     status of the effects of the previous adjtime call and there is no effect
     on the time correction as a result of this call.  If olddelta is not a
     NULL pointer, then the structure it points to will contain, upon return,
     the number of seconds and/or microseconds still to be corrected from the
     earlier call.  If olddelta 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 a process with the super-user privilege or a user with the
     CAP_TIME_MGT capability can 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
     The following error codes may be set in errno:

     EFAULT              delta or olddelta points outside the process's
                         allocated address space, or olddelta points to a
                         region of the process' allocated address space that
                         is not writable.


     EPERM               The calling process does not have the CAP_TIME_MGT
                         capability or super-user privilege to change the time
                         of day.

     EINVAL              The value of delta is not an acceptable value, it is
                         either too large or too small.

SEE ALSO
     date(1), gettimeofday(3C), capabilities(4)


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