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ADJTIME(2) FreeBSD System Calls Manual ADJTIME(2)
NAME
adjtime - correct the time to allow synchronization of the system clock
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/time.h>
int
adjtime(const struct timeval *delta, struct timeval *olddelta);
DESCRIPTION
The adjtime() system call 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 not a
null pointer, 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.
The adjtime() system call is restricted to the super-user.
RETURN VALUES
The adjtime() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
The adjtime() system call will fail if:
[EFAULT] An argument points outside the process's allocated
address space.
[EPERM] The process's effective user ID is not that of the
super-user.
SEE ALSO
date(1), gettimeofday(2)
R. Gusella and S. Zatti, TSP: The Time Synchronization Protocol for UNIX
4.3BSD.
HISTORY
The adjtime() system call appeared in 4.3BSD.
FreeBSD 14.0-RELEASE-p11 May 13, 2021 FreeBSD 14.0-RELEASE-p11