.\" Copyright (c) 1983, 1993
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.\"     @(#)fsync.2	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/sys/fsync.2,v 1.6.2.8 2001/12/14 18:34:00 ru Exp $
.\" $DragonFly: src/lib/libc/sys/fsync.2,v 1.2 2003/06/17 04:26:47 dillon Exp $
.\"
.Dd June 4, 1993
.Dt FSYNC 2
.Os
.Sh NAME
.Nm fsync
.Nd "synchronise changes to a file"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In 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
.Rv -std fsync
.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 syncer 4 ,
.Xr sync 8
.Sh HISTORY
The
.Fn fsync
function call appeared in
.Bx 4.2 .