4.3BSD/usr/man/man2/adjtime.2

.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)adjtime.2	1.3 (Berkeley) 5/15/86
.\"
.TH ADJTIME 2 "May 15, 1986"
.UC 6
.SH NAME
adjtime \- correct the time to allow synchronization of the system clock
.SH SYNOPSIS
.nf
.ft B
#include <sys/time.h>
.PP
.ft B
adjtime(delta, olddelta)
struct timeval *delta; 
struct timeval *olddelta;
.fi
.SH DESCRIPTION
.I Adjtime
makes small adjustments to the system time, as returned by
.IR gettimeofday (2),
advancing or retarding it
by the time specified by the timeval
\fIdelta\fP.
If \fIdelta\fP is negative, the clock is
slowed down by incrementing it more slowly than normal until
the correction is complete.
If \fIdelta\fP 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 \fIadjtime\fP
may not be finished when \fIadjtime\fP is called again.
If \fIolddelta\fP is non-zero,
then the structure pointed to will contain, upon return, the
number of microseconds still to be corrected
from the earlier call.
.PP
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.
.PP
The call 
.IR adjtime (2)
is restricted to the super-user.
.SH "RETURN VALUE
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 \fIerrno\fP.
.SH "ERRORS
The following error codes may be set in \fIerrno\fP:
.TP 15
[EFAULT]
An argument points outside the process's allocated address space.
.TP 15
[EPERM]
The process's effective user ID is not that of the super-user.
.SH "SEE ALSO"
date(1), gettimeofday(2), timed(8), timedc(8),
.br
\fITSP: The Time Synchronization Protocol for UNIX 4.3BSD\fP, 
R. Gusella and S. Zatti