1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)adjtime.2 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD: src/lib/libc/sys/adjtime.2,v 1.6.2.4 2001/12/14 18:34:00 ru Exp $ 34.\" 35.Dd June 4, 1993 36.Dt ADJTIME 2 37.Os 38.Sh NAME 39.Nm adjtime 40.Nd "correct the time to allow synchronization of the system clock" 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In sys/time.h 45.Ft int 46.Fn adjtime "const struct timeval *delta" "struct timeval *olddelta" 47.Sh DESCRIPTION 48.Fn Adjtime 49makes small adjustments to the system time, as returned by 50.Xr gettimeofday 2 , 51advancing or retarding it 52by the time specified by the timeval 53.Fa delta . 54If 55.Fa delta 56is negative, the clock is 57slowed down by incrementing it more slowly than normal until 58the correction is complete. 59If 60.Fa delta 61is positive, a larger increment than normal 62is used. 63The skew used to perform the correction is generally a fraction of one percent. 64Thus, the time is always 65a monotonically increasing function. 66A time correction from an earlier call to 67.Fn adjtime 68may not be finished when 69.Fn adjtime 70is called again. 71If 72.Fa olddelta 73is non-nil, 74the structure pointed to will contain, upon return, the 75number of microseconds still to be corrected 76from the earlier call. 77.Pp 78This call may be used by time servers that synchronize the clocks 79of computers in a local area network. 80Such time servers would slow down the clocks of some machines 81and speed up the clocks of others to bring them to the average network time. 82.Pp 83The call 84.Fn adjtime 85is restricted to the super-user. 86.Sh RETURN VALUES 87.Rv -std adjtime 88.Sh ERRORS 89.Fn Adjtime 90will fail if: 91.Bl -tag -width Er 92.It Bq Er EFAULT 93An argument points outside the process's allocated address space. 94.It Bq Er EPERM 95The process's effective user ID is not that of the super-user. 96.El 97.Sh SEE ALSO 98.Xr date 1 , 99.Xr gettimeofday 2 , 100.Xr timed 8 , 101.Xr timedc 8 102.Rs 103.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD" 104.%A R. Gusella 105.%A S. Zatti 106.Re 107.Sh HISTORY 108The 109.Fn adjtime 110function call appeared in 111.Bx 4.3 . 112