FDATASYNC(2) Linux Programmer s Manual FDATASYNC(2)

NAME fdatasync - synchronize a files 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 sys- tem 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() immedi- ately 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 synchro- nization.

BUGS Currently (Linux 2.2) fdatasync() is equivalent to fsync().

AVAILABILITY On POSIX systems on which fdatasync() is available, _POSIX_SYNCHRO- NIZED_IO is defined in <unistd.h> to a value greater than 0. (See also sysconf(3).)

CONFORMING TO POSIX.1-2001.

SEE ALSO fsync(2) sync_file_range(2), B.O. Gallmeister, POSIX.4, OReilly, pp. 220-223 and 343.

Linux 1.3.86 1996-04-13 FDATASYNC(2)