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, then the
adjtime() function in the standard C library will try to use the
clockctl(4) device if present, thus making possible for non privileged users to adjust the system time. If
clockctl(4) is not present or not accessible, then
adjtime() reverts to the
adjtime() system call, which is restricted to the super user.