adjtime - correct the time to allow synchronization of the
int adjtime(struct timeval *delta, struct timeval *old-
The adjtime() function adjusts the system's notion of the
current time as returned by gettimeofday(3C), advancing or
retarding it by the amount of time specified in the struct
timeval pointed to by delta.
The adjustment is effected by speeding up (if that amount of
time is positive) or slowing down (if that amount of time is
negative) the system's clock by some small percentage, gen-
erally a fraction of one percent. The time is always a mono-
tonically increasing function. A time correction from an
earlier call to adjtime() may not be finished when adjtime()
is called again.
If delta is 0, then olddelta returns the status of the
effects of the previous adjtime() call with no effect on the
time correction as a result of this call. If olddelta is not
a null pointer, then the structure it points to will con-
tain, upon successful return, the number of seconds and/or
microseconds still to be corrected from the earlier call. If
olddelta is a null pointer, the corresponding information
will not be returned.
This call may be used in 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 super-user may adjust the time of day.
The adjustment value will be silently rounded to the resolu-
tion of the system clock.
Upon successful completion, adjtime() returns 0. Otherwise,
it returns -1 and sets errno to indicate the error.
The adjtime() function will fail if:
The delta or olddelta argument points outside the
process's allocated address space, or olddelta points
to a region of the process's allocated address space
that is not writable.
The tv_usec member of delta is not within valid range
(-1000000 to 1000000).
EPERM The effective user of the calling process is not
Additionally, the adjtime() function will fail for 32-bit
The size of the tv_sec member of the timeval structure
pointed to by olddelta is too small to contain the
correct number of seconds.
Man(1) output converted with