— correct the time to allow
synchronization of the system clock
struct timeval *delta
struct timeval *olddelta
() makes small adjustments to the system time, as
returned by gettimeofday(2)
advancing or retarding it by the time specified by the timeval
. 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
() may not be finished when
() is called again. If delta
null, no adjustment is done. If olddelta
the structure pointed to will contain, upon return, the number of microseconds
still to be corrected from the earlier call. Setting the time with
will cancel 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
Only the superuser may adjust the time using the adjtime
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.
() will fail if:
- Either of the arguments point outside the process's
allocated address space.
- The delta() argument is non-null and the
process's effective user ID is not that of the superuser.
() function call appeared in
Other operating systems restrict calling adjtime
superuser and might not allow requesting the current correction without
specifying a new value.