FSYNC(2) Linux Programmer's Manual FSYNC(2)
NAME
fsync, fdatasync - synchronize a file's complete in-core state with
that on disk
SYNOPSIS
#include<unistd.h>
intfsync(int fd);
intfdatasync(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.
RETURNVALUE
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 synchro-
nization.
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).
CONFORMINGTO
POSIX.1b (formerly POSIX.4)
SEEALSO
bdflush(2), open(2), sync(2), mount(8), update(8), sync(8)
Linux 1.3.85 2001-04-18 FSYNC(2)
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