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.\" $OpenBSD: fsync.2,v 1.13 2013/08/14 06:32:28 jmc Exp $
.\" $NetBSD: fsync.2,v 1.4 1995/02/27 12:32:38 cgd Exp $
.\"
.\" Copyright (c) 1983, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)fsync.2 8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: August 14 2013 $
.Dt FSYNC 2
.Os
.Sh NAME
.Nm fsync ,
.Nm fdatasync
.Nd synchronize a file's in-core state with that on disk
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn fsync "int fd"
.Ft int
.Fn fdatasync "int fd"
.Sh DESCRIPTION
The
.Fn fsync
function causes all modified data and attributes of
.Fa fd
to be moved to a permanent storage device.
This normally results in all in-core modified copies
of buffers for the associated file to be written to a disk.
.Pp
The
.Fn fdatasync
function is similar to
.Fn fsync
except that it only guarantees modified data
.Pq and metadata necessary to read that data
is committed to storage.
Other file modifications may be left unsynchronized.
.Pp
.Fn fsync
and
.Fn fdatasync
should be used by programs that require a file to be in a known state,
for example, in building a simple transaction facility.
.Sh RETURN VALUES
.Rv -std fsync fdatasync
.Sh ERRORS
The
.Fn fsync
and
.Fn fdatasync
functions fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fd
is not a valid descriptor.
.It Bq Er EINVAL
.Fa fd
does not refer to a file which can be synchronized.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr sync 2 ,
.Xr sync 8
.Sh STANDARDS
The
.Fn fsync
and
.Fn fdatasync
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn fsync
system call first appeared in
.Bx 4.1c ,
and the
.Fn fdatasync
function has been available since
.Ox 5.4 .
.Sh BUGS
The
.Fn fdatasync
function is currently a wrapper around
.Fn fsync ,
so it synchronizes more state than necessary.
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