NAME
fsync, fdatasync
— synchronize a file's in-core
state with that on disk
SYNOPSIS
#include
<unistd.h>
int
fsync(int
fd);
int
fdatasync(int
fd);
DESCRIPTION
The
fsync()
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
a disk.
The
fdatasync()
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
unsynchronized.
fsync()
and fdatasync() should be used by programs that
require a file to be in a known state, for example, in building a simple
transaction facility.
If
fsync() or
fdatasync() fail with EIO,
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.
RETURN VALUES
The fsync() and
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.
ERRORS
The fsync() and
fdatasync() functions fail if:
- [
EBADF] - fd is not a valid descriptor.
- [
EINVAL] - fd does not refer to a file which can be synchronized.
- [
EIO] - An I/O error occurred while reading from or writing to the file system.
SEE ALSO
STANDARDS
The fsync() and
fdatasync() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
HISTORY
The fsync() system call first appeared in
4.1cBSD, and the fdatasync()
function has been available since OpenBSD 5.4.
BUGS
The fdatasync() function is currently a
wrapper around fsync(), so it synchronizes more
state than necessary.