|ADJTIME(2)||System Calls Manual||ADJTIME(2)|
adjtime — correct
the time to allow synchronization of the system clock
struct timeval *delta,
adjtime() makes small adjustments to the
system time, as returned by
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
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.
adjtime() will fail if:
R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX 4.3BSD.
adjtime() function call appeared in
|June 4, 1993||NetBSD-7.0.1|