.\"	$OpenBSD: fsync.2,v 1.5 1999/06/29 14:09:55 aaron 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.
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.\"     @(#)fsync.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt FSYNC 2
.Os
.Sh NAME
.Nm fsync
.Nd "synchronize a file's in-core state with that on disk"
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn fsync "int fd"
.Sh DESCRIPTION
.Fn fsync
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
.Fn fsync
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
A 0 value is returned on success.  A \-1 value indicates
an error.
.Sh ERRORS
The
.Fn fsync
fails if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fd
is not a valid descriptor.
.It Bq Er EINVAL
.Fa fd
refers to a socket, not to a file.
.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 ,
.Xr update 8
.Sh HISTORY
The
.Fn fsync
function call appeared in
.Bx 4.2 .