1.\" Copyright (c) 1980, 1991 Regents of the University of California. 2.\" 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. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)sync.2 6.3 (Berkeley) 3/10/91 33.\" 34.Dd March 10, 1991 35.Dt SYNC 2 36.Os BSD 4 37.Sh NAME 38.Nm sync 39.Nd "synchronize disk block in-core status with that on disk" 40.Sh SYNOPSIS 41.Fd #include <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. The kernel keeps this information in core to reduce 50the number of disk I/O transfers required by the system. 51As information in the cache is lost after a system crash a 52.Fn sync 53call is issued 54frequently 55by the user process 56.Xr update 8 57(about every 30 seconds). 58.Pp 59The function 60.Xr fsync 2 61may be used to synchronize individual file descriptor 62attributes. 63.Sh SEE ALSO 64.Xr fsync 2 , 65.Xr sync 8 , 66.Xr update 8 67.Sh BUGS 68.Fn Sync 69may return before the buffers are completely flushed. 70.Sh HISTORY 71A 72.Nm 73function call appeared in Version 6 AT&T UNIX. 74