1.\" $NetBSD: adjtime.2,v 1.15 2002/10/01 18:10:43 wiz 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. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)adjtime.2 8.1 (Berkeley) 6/4/93 35.\" 36.Dd June 4, 1993 37.Dt ADJTIME 2 38.Os 39.Sh NAME 40.Nm adjtime 41.Nd "correct the time to allow synchronization of the system clock" 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.Fd #include \*[Lt]sys/time.h\*[Gt] 46.Ft int 47.Fn adjtime "const struct timeval *delta" "struct timeval *olddelta" 48.Sh DESCRIPTION 49.Fn adjtime 50makes small adjustments to the system time, as returned by 51.Xr gettimeofday 2 , 52advancing or retarding it 53by the time specified by the timeval 54.Fa delta . 55If 56.Fa delta 57is negative, the clock is 58slowed down by incrementing it more slowly than normal until 59the correction is complete. 60If 61.Fa delta 62is positive, a larger increment than normal 63is used. 64The skew used to perform the correction is generally a fraction of one percent. 65Thus, the time is always 66a monotonically increasing function. 67A time correction from an earlier call to 68.Fn adjtime 69may not be finished when 70.Fn adjtime 71is called again. 72If 73.Fa olddelta 74is non-nil, 75the structure pointed to will contain, upon return, the 76number of microseconds still to be corrected 77from the earlier call. 78.Pp 79This call may be used by time servers that synchronize the clocks 80of computers in a local area network. 81Such time servers would slow down the clocks of some machines 82and speed up the clocks of others to bring them to the average network time. 83.Pp 84If the calling user is not the super user, then the 85.Fn adjtime 86function in the standard C library will try to use the 87.Xr clockctl 4 88device if present, thus making possible for non privileged users to 89adjust the system time. 90If 91.Xr clockctl 4 92is not present or not accessible, then 93.Fn adjust 94reverts to the 95.Fn adjust 96system call, which is restricted to the super user. 97.Sh RETURN VALUES 98A return value of 0 indicates that the call succeeded. 99A return value of -1 indicates that an error occurred, and in this 100case an error code is stored in the global variable 101.Va errno . 102.Sh ERRORS 103.Fn adjtime 104will fail if: 105.Bl -tag -width Er 106.It Bq Er EFAULT 107An argument points outside the process's allocated address space. 108.It Bq Er EPERM 109The process's effective user ID is not that of the super user. 110.El 111.Sh SEE ALSO 112.Xr date 1 , 113.Xr gettimeofday 2 , 114.Xr clockctl 4 , 115.Xr timed 8 , 116.Xr timedc 8 117.Rs 118.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD" 119.%A R. Gusella 120.%A S. Zatti 121.Re 122.Sh HISTORY 123The 124.Fn adjtime 125function call appeared in 126.Bx 4.3 . 127