1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. 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. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)sync.2 8.1 (Berkeley) 6/4/93 29.\" $FreeBSD: src/lib/libc/sys/sync.2,v 1.6.2.6 2001/12/14 18:34:01 ru Exp $ 30.\" $DragonFly: src/lib/libc/sys/sync.2,v 1.3 2006/02/17 19:35:06 swildner Exp $ 31.\" 32.Dd June 4, 1993 33.Dt SYNC 2 34.Os 35.Sh NAME 36.Nm sync 37.Nd "schedule filesystem updates" 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In unistd.h 42.Ft void 43.Fn sync void 44.Sh DESCRIPTION 45The 46.Fn sync 47function forces a write of dirty (modified) buffers 48in the block buffer cache out 49to disk. 50The kernel keeps this information in core to reduce 51the number of disk I/O transfers required by the system. 52As information in the cache is lost after a system crash a 53.Fn sync 54call is issued 55frequently 56by the user process 57.Xr syncer 4 58(about every 30 seconds). 59.Pp 60The function 61.Xr fsync 2 62may be used to synchronize individual file descriptor 63attributes. 64.Sh SEE ALSO 65.Xr fsync 2 , 66.Xr syncer 4 , 67.Xr sync 8 68.Sh HISTORY 69A 70.Fn sync 71function call appeared in 72.At v6 . 73.Sh BUGS 74.Fn Sync 75may return before the buffers are completely flushed. 76