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: src/lib/libc/sys/adjtime.2,v 1.6.2.4 2001/12/14 18:34:00 ru Exp $ 30.\" 31.Dd June 17, 2019 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 44.Fn Adjtime 45makes small adjustments to the system time, as returned by 46.Xr gettimeofday 2 , 47advancing or retarding it 48by the time specified by the timeval 49.Fa delta . 50If 51.Fa delta 52is negative, the clock is 53slowed down by incrementing it more slowly than normal until 54the correction is complete. 55If 56.Fa delta 57is positive, a larger increment than normal 58is used. 59The skew used to perform the correction is generally a fraction of one percent. 60Thus, the time is always 61a monotonically increasing function. 62A time correction from an earlier call to 63.Fn adjtime 64may not be finished when 65.Fn adjtime 66is called again. 67If 68.Fa olddelta 69is non-NULL, 70the structure pointed to will contain, upon return, the 71number of microseconds still to be corrected 72from the earlier call. 73.Pp 74This call may be used by time servers that synchronize the clocks 75of computers in a local area network. 76Such time servers would slow down the clocks of some machines 77and speed up the clocks of others to bring them to the average network time. 78.Pp 79The call 80.Fn adjtime 81is restricted to the super-user. 82.Sh RETURN VALUES 83.Rv -std adjtime 84.Sh ERRORS 85.Fn Adjtime 86will fail if: 87.Bl -tag -width Er 88.It Bq Er EFAULT 89An argument points outside the process's allocated address space. 90.It Bq Er EPERM 91The process's effective user ID is not that of the super-user. 92.El 93.Sh SEE ALSO 94.Xr date 1 , 95.Xr gettimeofday 2 96.Sh HISTORY 97The 98.Fn adjtime 99function call appeared in 100.Bx 4.3 . 101