ADJTIME(2) System Calls Manual ADJTIME(2)
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
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 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
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.
If the calling user is not the super user, then the adjtime() function in
the standard C library will try to use the clockctl(4) device if present,
thus making possible for non privileged users to adjust the system time.
If clockctl(4) is not present or not accessible, then adjtime() reverts
to the adjtime() system call, which is restricted to the super user.
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 6.1.5 June 4, 1993 NetBSD 6.1.5