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NAME
fdatasync - synchronize a file’s in-core data with that on disk
SYNOPSIS
#include <unistd.h>
int fdatasync(int fd);
DESCRIPTION
fdatasync() flushes all data buffers of a file to disk (before the
system call returns). It resembles fsync() but is not required to
update the metadata such as 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()
immediately in order to ensure that the written data is physically
stored on the harddisk. Unfortunately, fsync() 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.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.
ERRORS
EBADF fd is not a valid file descriptor open for writing.
EIO An error occurred during synchronization.
EROFS, EINVAL
fd is bound to a special file which does not support
synchronization.
BUGS
Currently (Linux 2.2) fdatasync() is equivalent to fsync().
AVAILABILITY
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).)
CONFORMING TO
POSIX1b (formerly POSIX.4)
SEE ALSO
fsync(2)
B.O. Gallmeister, POSIX.4, O’Reilly, pp. 220-223 and 343.