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.Dd May 13, 2021 29.Dt ADJTIME 2 30.Os 31.Sh NAME 32.Nm adjtime 33.Nd "correct the time to allow synchronization of the system clock" 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In sys/time.h 38.Ft int 39.Fn adjtime "const struct timeval *delta" "struct timeval *olddelta" 40.Sh DESCRIPTION 41The 42.Fn adjtime 43system call 44makes small adjustments to the system time, as returned by 45.Xr gettimeofday 2 , 46advancing or retarding it 47by the time specified by the timeval 48.Fa delta . 49If 50.Fa delta 51is negative, the clock is 52slowed down by incrementing it more slowly than normal until 53the correction is complete. 54If 55.Fa delta 56is positive, a larger increment than normal 57is used. 58The skew used to perform the correction is generally a fraction of one percent. 59Thus, the time is always 60a monotonically increasing function. 61A time correction from an earlier call to 62.Fn adjtime 63may not be finished when 64.Fn adjtime 65is called again. 66If 67.Fa olddelta 68is not a null pointer, 69the structure pointed to will contain, upon return, the 70number of microseconds still to be corrected 71from the earlier call. 72.Pp 73This call may be used by time servers that synchronize the clocks 74of computers in a local area network. 75Such time servers would slow down the clocks of some machines 76and speed up the clocks of others to bring them to the average network time. 77.Pp 78The 79.Fn adjtime 80system call 81is restricted to the super-user. 82.Sh RETURN VALUES 83.Rv -std adjtime 84.Sh ERRORS 85The 86.Fn adjtime 87system call will fail if: 88.Bl -tag -width Er 89.It Bq Er EFAULT 90An argument points outside the process's allocated address space. 91.It Bq Er EPERM 92The process's effective user ID is not that of the super-user. 93.El 94.Sh SEE ALSO 95.Xr date 1 , 96.Xr gettimeofday 2 97.Rs 98.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD" 99.%A R. Gusella 100.%A S. Zatti 101.Re 102.Sh HISTORY 103The 104.Fn adjtime 105system call appeared in 106.Bx 4.3 . 107