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	1	.\" $NetBSD: adjtime.2,v 1.5 1995/10/12 15:40:44 jtc Exp $
	2	.\"
	3	.\" Copyright (c) 1980, 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)adjtime.2 8.1 (Berkeley) 6/4/93
	35	.\"
	36	.Dd June 4, 1993
	37	.Dt ADJTIME 2
	38	.Os BSD 4.3
	39	.Sh NAME
	40	.Nm adjtime
	41	.Nd "correct the time to allow synchronization of the system clock"
	42	.Sh SYNOPSIS
	43	.Fd #include <sys/time.h>
	44	.Ft int
	45	.Fn adjtime "const struct timeval delta" "struct timeval olddelta"
	46	.Sh DESCRIPTION
	47	.Fn Adjtime
	48	makes small adjustments to the system time, as returned by
	49	.Xr gettimeofday 2 ,
	50	advancing or retarding it
	51	by the time specified by the timeval
	52	.Fa delta .
	53	If
	54	.Fa delta
	55	is negative, the clock is
	56	slowed down by incrementing it more slowly than normal until
	57	the correction is complete.
	58	If
	59	.Fa delta
	60	is positive, a larger increment than normal
	61	is used.
	62	The skew used to perform the correction is generally a fraction of one percent.
	63	Thus, the time is always
	64	a monotonically increasing function.
	65	A time correction from an earlier call to
	66	.Fn adjtime
	67	may not be finished when
	68	.Fn adjtime
	69	is called again.
	70	If
	71	.Fa olddelta
	72	is non-nil,
	73	the structure pointed to will contain, upon return, the
	74	number of microseconds still to be corrected
	75	from the earlier call.
	76	.Pp
	77	This call may be used by time servers that synchronize the clocks
	78	of computers in a local area network.
	79	Such time servers would slow down the clocks of some machines
	80	and speed up the clocks of others to bring them to the average network time.
	81	.Pp
	82	The call
	83	.Fn adjtime
	84	is restricted to the super-user.
	85	.Sh RETURN VALUES
	86	A return value of 0 indicates that the call succeeded.
	87	A return value of -1 indicates that an error occurred, and in this
	88	case an error code is stored in the global variable
	89	.Va errno .
	90	.Sh ERRORS
	91	.Fn Adjtime
	92	will fail if:
	93	.Bl -tag -width Er
	94	.It Bq Er EFAULT
	95	An argument points outside the process's allocated address space.
	96	.It Bq Er EPERM
	97	The process's effective user ID is not that of the super-user.
	98	.El
	99	.Sh SEE ALSO
	100	.Xr date 1 ,
	101	.Xr gettimeofday 2 ,
	102	.Xr timed 8 ,
	103	.Xr timedc 8
	104	.Rs
	105	.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
	106	.%A R. Gusella
	107	.%A S. Zatti
	108	.Re
	109	.Sh HISTORY
	110	The
	111	.Fn adjtime
	112	function call appeared in
	113	.Bx 4.3 .