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. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)adjtime.2 8.1 (Berkeley) 6/4/93 29.\" $FreeBSD$ 30.\" 31.Dd June 4, 1993 32.Dt ADJTIME 2 33.Os 34.Sh NAME 35.Nm adjtime 36.Nd "correct the time to allow synchronization of the system clock" 37.Sh LIBRARY 38.Lb libc 39.Sh SYNOPSIS 40.In sys/time.h 41.Ft int 42.Fn adjtime "const struct timeval *delta" "struct timeval *olddelta" 43.Sh DESCRIPTION 44The 45.Fn adjtime 46system call 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 not a null pointer, 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 82.Fn adjtime 83system call 84is restricted to the super-user. 85.Sh RETURN VALUES 86.Rv -std adjtime 87.Sh ERRORS 88The 89.Fn adjtime 90system call will 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 110system call appeared in 111.Bx 4.3 . 112