1.\" $NetBSD: sync.2,v 1.4 1995/02/27 12:38:41 cgd 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.\" @(#)sync.2 8.1 (Berkeley) 6/4/93 35.\" 36.Dd June 4, 1993 37.Dt SYNC 2 38.Os BSD 4 39.Sh NAME 40.Nm sync 41.Nd "synchronize disk block in-core status with that on disk" 42.Sh SYNOPSIS 43.Fd #include <unistd.h> 44.Ft void 45.Fn sync void 46.Sh DESCRIPTION 47The 48.Fn sync 49function forces a write of dirty (modified) buffers 50in the block buffer cache out 51to disk. The kernel keeps this information in core to reduce 52the number of disk I/O transfers required by the system. 53As information in the cache is lost after a system crash a 54.Fn sync 55call is issued 56frequently 57by the user process 58.Xr update 8 59(about every 30 seconds). 60.Pp 61The function 62.Xr fsync 2 63may be used to synchronize individual file descriptor 64attributes. 65.Sh SEE ALSO 66.Xr fsync 2 , 67.Xr sync 8 , 68.Xr update 8 69.Sh BUGS 70.Fn Sync 71may return before the buffers are completely flushed. 72.Sh HISTORY 73A 74.Fn sync 75function call appeared in 76.At v6 . 77