mirror of https://github.com/mkerrisk/man-pages
103 lines
3.2 KiB
Groff
103 lines
3.2 KiB
Groff
.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (C) 1996 Andries Brouwer (aeb@cwi.nl)
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.\" Copyright (C) 1996 Markus Kuhn.
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.\"
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.\" [This version merged from two independently written pages - aeb]
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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.\" manual page may be incorrect or out-of-date.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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.\" 1996-04-12 Andries Brouwer <aeb@cwi.nl>
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.\" 1996-04-13 Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
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.\"
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.TH FDATASYNC 2 1996-04-13 "Linux" "Linux Programmer's Manual"
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.SH NAME
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fdatasync \- synchronize a file's in-core data 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 fdatasync(int " fd );
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.SH DESCRIPTION
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.BR fdatasync ()
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flushes all data buffers of a file to disk (before the system
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call returns).
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It resembles
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.BR fsync (2)
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but is not required to update metadata such as the file last access time.
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Applications that access databases or log files often write a tiny
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data fragment (e.g., one line in a log file) and then call
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.BR fsync (2)
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immediately in order to ensure that the written data is physically
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stored on the harddisk.
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Unfortunately,
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.BR fsync (2)
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will always initiate two write operations: one for the newly written
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data and another one in order to update the modification time stored
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in the inode.
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If the modification time is not a part of the transaction
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concept
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.BR fdatasync ()
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can be used to avoid unnecessary inode disk write operations.
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.SH "RETURN VALUE"
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On success, zero is returned.
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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 "CONFORMING TO"
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POSIX.1-2001.
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.SH AVAILABILITY
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On POSIX systems on which
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.BR fdatasync ()
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is available,
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.B _POSIX_SYNCHRONIZED_IO
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is defined in
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.I <unistd.h>
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to a value greater than 0.
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(See also
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.BR sysconf (3).)
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.\" POSIX.1-2001: It shall be defined to -1 or 0 or 200112L.
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.\" -1: unavailable, 0: ask using sysconf().
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.\" glibc defines them to 1.
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.SH NOTES
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In Linux 2.2 and earlier,
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.BR fdatasync ()
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is equivalent to
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.BR fsync (2),
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and so has no performance advantage.
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.SH "SEE ALSO"
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.BR fsync (2),
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.BR sync_file_range (2)
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.br
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B.O. Gallmeister, POSIX.4, O'Reilly, pp. 220-223 and 343.
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