1.\" $OpenBSD: adjtime.2,v 1.10 2000/10/18 05:12:08 aaron Exp $ 2.\" $NetBSD: adjtime.2,v 1.5 1995/10/12 15:40:44 jtc Exp $ 3.\" 4.\" Copyright (c) 1980, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)adjtime.2 8.1 (Berkeley) 6/4/93 36.\" 37.Dd June 4, 1993 38.Dt ADJTIME 2 39.Os 40.Sh NAME 41.Nm adjtime 42.Nd "correct the time to allow synchronization of the system clock" 43.Sh SYNOPSIS 44.Fd #include <sys/time.h> 45.Ft int 46.Fn adjtime "const struct timeval *delta" "struct timeval *olddelta" 47.Sh DESCRIPTION 48.Fn adjtime 49makes small adjustments to the system time, as returned by 50.Xr gettimeofday 2 , 51advancing or retarding it by the time specified by the timeval 52.Fa delta . 53If 54.Fa delta 55is negative, the clock is slowed down by incrementing it more slowly 56than normal until the correction is complete. 57If 58.Fa delta 59is positive, a larger increment than normal is used. 60The skew used to perform the correction is generally a fraction of one percent. 61Thus, the time is always a 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, the structure pointed to will contain, upon return, the 70number of microseconds still to be corrected from the earlier call. 71.Pp 72This call may be used by time servers that synchronize the clocks 73of computers in a local area network. 74Such time servers would slow down the clocks of some machines 75and speed up the clocks of others to bring them to the average network time. 76.Pp 77The call 78.Fn adjtime 79is restricted to the superuser. 80.Sh RETURN VALUES 81A return value of 0 indicates that the call succeeded. 82A return value of \-1 indicates that an error occurred, and in this 83case an error code is stored in the global variable 84.Va errno . 85.Sh ERRORS 86.Fn adjtime 87will fail if: 88.Bl -tag -width Er 89.It Bq Er EFAULT 90Either of the arguments point outside the process's allocated address space. 91.It Bq Er EPERM 92The process's effective user ID is not that of the superuser. 93.El 94.Sh SEE ALSO 95.Xr date 1 , 96.Xr gettimeofday 2 , 97.Xr timed 8 , 98.Xr timedc 8 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 107function call appeared in 108.Bx 4.3 . 109