fdatasync(2) -- Linux man page
NAMEfdatasync - synchronize a file's in-core data with that on disk
DESCRIPTIONfdatasync 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 VALUEOn success, zero is returned. On error, -1 is returned, and errno is set appropriately.
- fd is not a valid file descriptor open for writing.
- EROFS, EINVAL
- fd is bound to a special file which does not support synchronization.
- An error occurred during synchronization.
BUGSCurrently (Linux 2.2) fdatasync is equivalent to fsync.
AVAILABILITYOn 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 TOPOSIX1b (formerly POSIX.4)
SEE ALSOfsync(2), B.O. Gallmeister, POSIX.4, O'Reilly, pp. 220-223 and 343.