— synchronize a file's in-core
state with that on disk
function causes all modified data and attributes of fd
to be moved to a permanent storage device. This normally results in all
in-core modified copies of buffers for the associated file to be written to
function is similar to
fsync() except that it only
guarantees modified data (and metadata necessary to read that data) is
committed to storage. Other file modifications may be left
fdatasync() should be used by programs that
require a file to be in a known state, for example, in building a simple
fdatasync() fail with
the state of the on-disk data may have been only partially written. To guard
against potential inconsistency, future calls will continue failing until
all references to the file are closed.
fdatasync() functions return the value 0 if
successful; otherwise the value -1 is returned and the global
variable errno is set to indicate the error.
fdatasync() functions fail if:
- fd is not a valid descriptor.
- fd does not refer to a file which can be synchronized.
- An I/O error occurred while reading from or writing to the file system.
fdatasync() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
fsync() system call first appeared in
4.1cBSD, and the
function has been available since OpenBSD 5.4.
fdatasync() function is currently a
fsync(), so it synchronizes more
state than necessary.