1.\" $OpenBSD: sync.8,v 1.9 1999/08/17 14:04:02 aaron Exp $ 2.\" $NetBSD: sync.8,v 1.6 1995/03/21 09:11:35 cgd 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.\" @(#)sync.8 8.1 (Berkeley) 5/31/93 36.\" 37.Dd May 31, 1993 38.Dt SYNC 8 39.Os 40.Sh NAME 41.Nm sync 42.Nd force completion of pending disk writes (flush cache) 43.Sh SYNOPSIS 44.Nm sync 45.Sh DESCRIPTION 46The 47.Nm 48utility can be called to ensure that all disk writes have been completed before 49the processor is halted in a way not suitably done by 50.Xr reboot 8 51or 52.Xr halt 8 . 53Generally, it is preferable to use 54.Xr reboot 8 55or 56.Xr halt 8 57to shut down the system, 58as they may perform additional actions 59such as resynchronizing the hardware clock 60and flushing internal caches before performing a final 61.Nm sync . 62.Pp 63.Nm 64utilizes the 65.Xr sync 2 66function call. 67.Sh SEE ALSO 68.Xr fsync 2 , 69.Xr sync 2 , 70.Xr halt 8 , 71.Xr reboot 8 , 72.Xr update 8 73.Sh HISTORY 74A 75.Nm 76command appeared in 77.At v6 . 78