1.\" Copyright (c) 1980, 1991 Regents of the University of California. 2.\" 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.\" from: @(#)adjtime.2 1.7 (Berkeley) 3/10/91 33.\" $Id: adjtime.2,v 1.2 1993/08/01 07:43:24 mycroft Exp $ 34.\" 35.Dd March 10, 1991 36.Dt ADJTIME 2 37.Os BSD 4.3 38.Sh NAME 39.Nm adjtime 40.Nd "correct the time to allow synchronization of the system clock" 41.Sh SYNOPSIS 42.Fd #include <sys/time.h> 43.Ft int 44.Fn adjtime "struct timeval *delta" "struct timeval *olddelta" 45.Sh DESCRIPTION 46.Fn Adjtime 47makes small adjustments to the system time, as returned by 48.Xr gettimeofday 2 , 49advancing or retarding it 50by the time specified by the timeval 51.Fa delta . 52If 53.Fa delta 54is negative, the clock is 55slowed down by incrementing it more slowly than normal until 56the correction is complete. 57If 58.Fa delta 59is positive, a larger increment than normal 60is used. 61The skew used to perform the correction is generally a fraction of one percent. 62Thus, the time is always 63a monotonically increasing function. 64A time correction from an earlier call to 65.Fn adjtime 66may not be finished when 67.Fn adjtime 68is called again. 69If 70.Fa olddelta 71is non-nil, 72the structure pointed to will contain, upon return, the 73number of microseconds still to be corrected 74from the earlier call. 75.Pp 76This call may be used by time servers that synchronize the clocks 77of computers in a local area network. 78Such time servers would slow down the clocks of some machines 79and speed up the clocks of others to bring them to the average network time. 80.Pp 81The call 82.Fn adjtime 83is restricted to the super-user. 84.Sh RETURN VALUES 85A return value of 0 indicates that the call succeeded. 86A return value of -1 indicates that an error occurred, and in this 87case an error code is stored in the global variable 88.Va errno . 89.Sh ERRORS 90.Fn Adjtime 91will fail if: 92.Bl -tag -width Er 93.It Bq Er EFAULT 94An argument points outside the process's allocated address space. 95.It Bq Er EPERM 96The process's effective user ID is not that of the super-user. 97.El 98.Sh SEE ALSO 99.Xr date 1 , 100.Xr gettimeofday 2 , 101.Xr timed 8 , 102.Xr timedc 8 , 103.Rs 104.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD" 105.%A R. Gusella 106.%A S. Zatti 107.Re 108.Sh HISTORY 109The 110.Nm 111function call appeared in 112.Bx 4.3 . 113