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 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.
RETURN VALUES
A return value of 0 indicates that the call succeeded. A return value of -1 indicates that an error occurred, and in this case an error code is stored in the global variable errno.
ERRORS
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.
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.