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.\" 30.Dd May 13, 2021 31.Dt ADJTIME 2 32.Os 33.Sh NAME 34.Nm adjtime 35.Nd "correct the time to allow synchronization of the system clock" 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In sys/time.h 40.Ft int 41.Fn adjtime "const struct timeval *delta" "struct timeval *olddelta" 42.Sh DESCRIPTION 43The 44.Fn adjtime 45system call 46makes small adjustments to the system time, as returned by 47.Xr gettimeofday 2 , 48advancing or retarding it 49by the time specified by the timeval 50.Fa delta . 51If 52.Fa delta 53is negative, the clock is 54slowed down by incrementing it more slowly than normal until 55the correction is complete. 56If 57.Fa delta 58is positive, a larger increment than normal 59is used. 60The skew used to perform the correction is generally a fraction of one percent. 61Thus, the time is always 62a monotonically increasing function. 63A time correction from an earlier call to 64.Fn adjtime 65may not be finished when 66.Fn adjtime 67is called again. 68If 69.Fa olddelta 70is not a null pointer, 71the structure pointed to will contain, upon return, the 72number of microseconds still to be corrected 73from the earlier call. 74.Pp 75This call may be used by time servers that synchronize the clocks 76of computers in a local area network. 77Such time servers would slow down the clocks of some machines 78and speed up the clocks of others to bring them to the average network time. 79.Pp 80The 81.Fn adjtime 82system call 83is restricted to the super-user. 84.Sh RETURN VALUES 85.Rv -std adjtime 86.Sh ERRORS 87The 88.Fn adjtime 89system call will fail if: 90.Bl -tag -width Er 91.It Bq Er EFAULT 92An argument points outside the process's allocated address space. 93.It Bq Er EPERM 94The process's effective user ID is not that of the super-user. 95.El 96.Sh SEE ALSO 97.Xr date 1 , 98.Xr gettimeofday 2 99.Rs 100.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD" 101.%A R. Gusella 102.%A S. Zatti 103.Re 104.Sh HISTORY 105The 106.Fn adjtime 107system call appeared in 108.Bx 4.3 . 109