fdatasync — synchronize a file's in-core data with that on disk
#include <unistd.h>
int
fdatasync( |
int | fd) ; |
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fdatasync
() flushes all data
buffers of a file to disk (before the system call returns).
It resembles fsync(2) but is not
required to update metadata such as the file last access
time.
Applications that access databases or log files often
write a tiny data fragment (e.g., one line in a log file) and
then call fsync(2) immediately in
order to ensure that the written data is physically stored on
the harddisk. Unfortunately, fsync(2) will always
initiate two write operations: one for the newly written data
and another one in order to update the modification time
stored in the inode. If the modification time is not a part
of the transaction concept fdatasync
() can be used to avoid
unnecessary inode disk write operations.
On success, zero is returned. On error, −1 is
returned, and errno
is set
appropriately.
fd
is not a
valid file descriptor open for writing.
An error occurred during synchronization.
fd
is bound
to a special file which does not support
synchronization.
On POSIX systems on which fdatasync
() is available, _POSIX_SYNCHRONIZED_IO
is defined in
<
unistd.h
>
to a value greater than 0. (See also sysconf(3).)
In Linux 2.2 and earlier, fdatasync
() is equivalent to fsync(2), and so has no
performance advantage.
B.O. Gallmeister, POSIX.4, O'Reilly, pp. 220-223 and 343.
Copyright (C) 1996 Andries Brouwer (aeb@cwi.nl) Copyright (C) 1996 Markus Kuhn. [This version merged from two independently written pages - aeb] Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. 1996-04-12 Andries Brouwer <aeb@cwi.nl> 1996-04-13 Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de> |