.\"	$OpenBSD: sync.2,v 1.9 2003/06/02 20:18:39 millert Exp $
.\"	$NetBSD: sync.2,v 1.4 1995/02/27 12:38:41 cgd Exp $
.\"
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.\"     @(#)sync.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt SYNC 2
.Os
.Sh NAME
.Nm sync
.Nd "synchronize disk block in-core status with that on disk"
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft void
.Fn sync void
.Sh DESCRIPTION
The
.Fn sync
function forces a write of dirty (modified) buffers
in the block buffer cache out to disk.
The kernel keeps this information in core to reduce
the number of disk I/O transfers required by the system.
As information in the cache is lost after a system crash a
.Fn sync
call is issued frequently by the user process
.Xr update 8
(about every 30 seconds).
.Pp
The function
.Xr fsync 2
may be used to synchronize individual file descriptor attributes.
.Sh SEE ALSO
.Xr fsync 2 ,
.Xr sync 8 ,
.Xr update 8
.Sh HISTORY
A
.Fn sync
function call appeared in
.At v2 .
.Sh BUGS
.Fn sync
may return before the buffers are completely flushed.