NAME
adjtime
—
correct the time to allow
synchronization of the system clock
SYNOPSIS
#include
<sys/time.h>
int
adjtime
(const
struct timeval *delta,
struct timeval
*olddelta);
DESCRIPTION
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 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
adjtime
()
function.
RETURN VALUES
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.
ERRORS
adjtime
() will fail if:
- [
EFAULT
] - Either of the arguments point outside the process's allocated address space.
- [
EINVAL
] - The delta argument is
non-
NULL
and specifies a microsecond value less than zero or greater than or equal to one million. - [
EINVAL
] - The delta argument is
non-
NULL
and represents an adjustment greater thanINT64_MAX
microseconds or less thanINT64_MIN
microseconds. - [
EPERM
] - The delta argument is
non-
NULL
and the process's effective user ID is not that of the superuser.
SEE ALSO
HISTORY
The adjtime
() function call appeared in
4.3BSD.
CAVEATS
Other operating systems restrict calling
adjtime
() to the superuser and might not allow
requesting the current correction without specifying a new value.