|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
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
NULL, no adjustment
is done. If olddelta is
NULL, the number of microseconds still to be
corrected from the earlier call is stored into
*olddelta. Setting the time with
settimeofday(2) cancels any
in-progress time adjustment.
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.
Only the superuser may adjust the time using the
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
adjtime() will fail if:
NULLand specifies a microsecond value less than zero or greater than or equal to one million.
NULLand represents an adjustment greater than
INT64_MAXmicroseconds or less than
NULLand the process's effective user ID is not that of the superuser.
adjtime() function call appeared in
Other operating systems restrict calling
adjtime() to the superuser and might not allow
requesting the current correction without specifying a new value.
|March 26, 2019||OpenBSD-current|