1.\" $NetBSD: adjtime.2,v 1.21 2015/12/07 23:20:57 pgoyette Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)adjtime.2 8.1 (Berkeley) 6/4/93 31.\" 32.Dd December 8, 2015 33.Dt ADJTIME 2 34.Os 35.Sh NAME 36.Nm adjtime 37.Nd "correct the time to allow synchronization of the system clock" 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In sys/time.h 42.Ft int 43.Fn adjtime "const 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 80If the calling user is not the super user, the 81.Fn adjtime 82system call will fail, and the 83.Fn adjtime 84function in the standard C library will try to use the 85.Xr clockctl 4 86device if present, thus making it possible for non privileged users to 87adjust the system time. 88If 89.Xr clockctl 4 90is not present or not accessible, then 91.Fn adjtime 92returns 93.Er EPERM . 94.Sh RETURN VALUES 95A return value of 0 indicates that the call succeeded. 96A return value of \-1 indicates that an error occurred, and in this 97case an error code is stored in the global variable 98.Va errno . 99.Sh ERRORS 100.Fn adjtime 101will fail if: 102.Bl -tag -width Er 103.It Bq Er EFAULT 104An argument points outside the process's allocated address space. 105.It Bq Er EPERM 106The process's effective user ID is not that of the super user. 107.El 108.Sh SEE ALSO 109.Xr date 1 , 110.Xr gettimeofday 2 , 111.Xr clockctl 4 , 112.Xr timed 8 , 113.Xr timedc 8 114.Rs 115.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD" 116.%A R. Gusella 117.%A S. Zatti 118.Re 119.Sh HISTORY 120The 121.Fn adjtime 122function call appeared in 123.Bx 4.3 . 124