2004-11-03 13:51:07 +00:00
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Modified 21 Aug 1994 by Michael Chastain <mec@shell.portal.com>:
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.\" Removed note about old libc (pre-4.5.26) translating to 'sync'.
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.\" Modified 15 Apr 1995 by Michael Chastain <mec@shell.portal.com>:
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.\" Added `see also' section.
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.\" Modified 13 Apr 1996 by Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
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.\" Added remarks about fdatasync.
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.\" Modified 31 Jan 1997 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 18 Apr 2001 by Andi Kleen
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.\" Fix description to describe what it really does; add a few caveats.
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.\"
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.TH FSYNC 2 2001-04-18 "Linux 1.3.85" "Linux Programmer's Manual"
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.SH NAME
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fsync, fdatasync \- synchronize a file's complete in-core state with that on disk
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.SH SYNOPSIS
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.B #include <unistd.h>
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.sp
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.BI "int fsync(int " fd );
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.sp
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.BI "int fdatasync(int " fd );
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.SH DESCRIPTION
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.B fsync
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copies all in-core parts of a file to disk, and waits until the
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device reports that all parts are on stable storage.
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It also updates metadata stat information. It does not necessarily ensure
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that the entry in the directory containing the file has also reached disk.
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For that an explicit
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.B fsync
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on the file descriptor of the directory is also needed.
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.B fdatasync
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does the same as
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.B fsync
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2005-07-19 07:15:17 +00:00
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but only flushes user data, not the meta data like the st_atime or
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st_mtime
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(respectively, time of last access and
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time of last modification; see
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.BR stat (2)) .
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2004-11-03 13:51:07 +00:00
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.SH "RETURN VALUE"
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On success, zero is returned. On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EBADF
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.I fd
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is not a valid file descriptor open for writing.
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.TP
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.B EIO
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An error occurred during synchronization.
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.TP
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.BR EROFS ", " EINVAL
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.I fd
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is bound to a special file which does not support synchronization.
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.SH NOTES
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In case the hard disk has write cache enabled,
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the data may not really be on permanent storage when
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.BR fsync / fdatasync
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return.
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.\" See
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.\" .BR hdparm (8)
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.\" for how to disable that cache for IDE disks.
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.LP
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When an ext2 file system is mounted with the
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.I sync
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option, directory entries are also implicitly synced by
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.BR fsync .
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.LP
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On kernels before 2.4,
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.B fsync
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on big files can be inefficient.
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An alternative might be to use the
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.I O_SYNC
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flag to
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.BR open (2).
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.SH "CONFORMING TO"
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POSIX.1b (formerly POSIX.4)
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.SH "SEE ALSO"
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.BR bdflush (2),
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.BR open (2),
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2005-07-19 07:15:17 +00:00
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.BR sync (2),
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2004-11-03 13:51:07 +00:00
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.BR mount (8),
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.BR sync (8),
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.BR update (8)
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