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ADJTIME(2) NetBSD System Calls Manual ADJTIME(2)
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by Kimmo Suominen.
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adjtime -- correct the time to allow synchronization of the system clock
Standard C Library (libc, -lc)
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 incre-
menting 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 correc-
tion from an earlier call to adjtime() may not be finished when adjtime()
is called again. If olddelta is non-nil, the structure pointed to will
contain, upon return, the number of microseconds still to be corrected
from the earlier call.
This call may be used by time servers that synchronize the clocks of com-
puters 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.
If the calling user is not the super user, the adjtime() system call will
fail, and the adjtime() function in the standard C library will try to
use the clockctl(4) device if present, thus making it possible for non
privileged users to adjust the system time. If clockctl(4) is not
present or not accessible, then adjtime() returns EPERM.
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.
adjtime() will fail if:
[EFAULT] An argument points outside the process's allocated
[EPERM] The process's effective user ID is not that of the
date(1), gettimeofday(2), clockctl(4), timed(8), timedc(8)
R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX
The adjtime() function call appeared in 4.3BSD.
NetBSD 9.0 December 8, 2015 NetBSD 9.0