fsync(2) -- Linux man page
NAME
fsync, fdatasync - synchronize a file's complete in-core state with that on disk
SYNOPSIS
#include <unistd.h>
int fsync(int fd);
int fdatasync(int fd);
DESCRIPTION
fsync
copies all in-core parts of a file to disk, and waits until the
device reports that all parts are on stable storage.
It also updates metadata stat information. It does not necessarily ensure
that the entry in the directory containing the file has also reached disk.
For that an explicit
fsync
on the file descriptor of the directory is also needed.
fdatasync
does the same as
fsync
but only flushes user data, not the meta data like the mtime or atime.
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.
- EROFS, EINVAL
-
fd
is bound to a special file which does not support synchronization.
- EIO
-
An error occurred during synchronization.
NOTES
In case the hard disk has write cache enabled,
the data may not really be on permanent storage when
fsync/fdatasync
return.
When an ext2 file system is mounted with the
sync
option, directory entries are also implicitly synced by
fsync.
On kernels before 2.4,
fsync
on big files can be inefficient.
An alternative might be to use the
O_SYNC
flag to
open(2).
CONFORMING TO
POSIX.1b (formerly POSIX.4)
SEE ALSO
bdflush(2),
open(2),
sync(2),
mount(8),
update(8),
sync(8)
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