1.\" Copyright (c) 1980, 1991 Regents of the University of California. 2.\" 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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)adjtime.2 1.7 (Berkeley) 3/10/91 33.\" 34.Dd March 10, 1991 35.Dt ADJTIME 2 36.Os BSD 4.3 37.Sh NAME 38.Nm adjtime 39.Nd "correct the time to allow synchronization of the system clock" 40.Sh SYNOPSIS 41.Fd #include <sys/time.h> 42.Ft int 43.Fn adjtime "struct timeval *delta" "struct timeval *olddelta" 44.Sh DESCRIPTION 45.Fn Adjtime 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 non-nil, 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 call 81.Fn adjtime 82is restricted to the super-user. 83.Sh RETURN VALUES 84A return value of 0 indicates that the call succeeded. 85A return value of -1 indicates that an error occurred, and in this 86case an error code is stored in the global variable 87.Va errno . 88.Sh ERRORS 89.Fn Adjtime 90will 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.Nm 110function call appeared in 111.Bx 4.3 . 112