1.\" $OpenBSD: sync.2,v 1.12 2011/04/29 07:12:44 jmc Exp $ 2.\" $NetBSD: sync.2,v 1.4 1995/02/27 12:38:41 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. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)sync.2 8.1 (Berkeley) 6/4/93 32.\" 33.Dd $Mdocdate: April 29 2011 $ 34.Dt SYNC 2 35.Os 36.Sh NAME 37.Nm sync 38.Nd "synchronize disk block in-core status with that on disk" 39.Sh SYNOPSIS 40.Fd #include <unistd.h> 41.Ft void 42.Fn sync void 43.Sh DESCRIPTION 44The 45.Fn sync 46function forces a write of dirty (modified) buffers 47in the block buffer cache out to disk. 48The kernel keeps this information in core to reduce 49the number of disk I/O transfers required by the system. 50As information in the cache is lost after a system crash a 51.Fn sync 52call is issued frequently by the in-kernel process update 53(about every 30 seconds). 54.Pp 55The function 56.Xr fsync 2 57may be used to synchronize individual file descriptor attributes. 58.Sh SEE ALSO 59.Xr fsync 2 , 60.Xr sync 8 61.Sh HISTORY 62A 63.Fn sync 64function call appeared in 65.At v2 . 66.Sh BUGS 67.Fn sync 68may return before the buffers are completely flushed. 69