adjtime —
correct the time to allow synchronization of the
system clock
#include
<sys/time.h>
int
adjtime(
const
struct timeval *delta,
struct timeval
*olddelta);
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
delta is null, no adjustment is done. If
olddelta is non-null, the structure pointed
to will contain, upon return, the number of microseconds still to be corrected
from the earlier call. Setting the time with
settimeofday(2) 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
network time.
Only the superuser may adjust the time using the
adjtime() function.
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:
-
-
- [
EFAULT]
- Either of the arguments point outside the process's allocated address
space.
-
-
- [
EPERM]
- The
delta() argument is non-null and
the process's effective user ID is not that of the superuser.
date(1),
adjfreq(2),
gettimeofday(2),
ntpd(8)
The
adjtime() function call appeared in
4.3BSD.
Other operating systems restrict calling
adjtime to the superuser and might not
allow requesting the current correction without specifying a new value.
![[OpenBSD]](/openbsd.gif){kind=small}