| ADJTIME(2) | System Calls Manual | ADJTIME(2) | 
adjtime —
#include <sys/time.h>
int
  
  adjtime(const
    struct timeval *delta,
    struct timeval
    *olddelta);
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 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. 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. If
  olddelta is non-nil, 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.
If the calling user is not the super user, the
    adjtime() system call will fail, and the
    adjtime() function in the standard C library will
    try to use the clockctl(4)
    device if present, thus making it possible for non privileged users to
    adjust the system time. If
    clockctl(4) is not present
    or not accessible, then adjtime() returns
    EPERM.
adjtime() will fail if:
R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX 4.3BSD.
adjtime() function call appeared in
  4.3BSD.
| December 8, 2015 | NetBSD 9.4 |