1.\" $OpenBSD: sync.2,v 1.2 1998/07/06 18:28:49 deraadt 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. 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.2 8.1 (Berkeley) 6/4/93 36.\" 37.Dd June 4, 1993 38.Dt SYNC 2 39.Os BSD 4 40.Sh NAME 41.Nm sync 42.Nd "synchronize disk block in-core status with that on disk" 43.Sh SYNOPSIS 44.Fd #include <unistd.h> 45.Ft void 46.Fn sync void 47.Sh DESCRIPTION 48The 49.Fn sync 50function forces a write of dirty (modified) buffers 51in the block buffer cache out 52to disk. The kernel keeps this information in core to reduce 53the number of disk I/O transfers required by the system. 54As information in the cache is lost after a system crash a 55.Fn sync 56call is issued 57frequently 58by the user process 59.Xr update 8 60(about every 30 seconds). 61.Pp 62The function 63.Xr fsync 2 64may be used to synchronize individual file descriptor 65attributes. 66.Sh SEE ALSO 67.Xr fsync 2 , 68.Xr sync 8 , 69.Xr update 8 70.Sh BUGS 71.Fn Sync 72may return before the buffers are completely flushed. 73.Sh HISTORY 74A 75.Fn sync 76function call appeared in 77.At v6 . 78