FSYNC(3C) Standard C Library Functions FSYNC(3C)

NAME

fsync - synchronize changes to a file

SYNOPSIS

#include <unistd.h>

int fsync(int fildes);

DESCRIPTION

The fsync() function moves all modified data and attributes of the file
descriptor fildes to a storage device. When fsync() returns, all in-
memory modified copies of buffers associated with fildes have been
written to the physical medium. The fsync() function is different from
sync(), which schedules disk I/O for all files but returns before the
I/O completes. The fsync() function forces all outstanding data
operations to synchronized file integrity completion (see fcntl.h(3HEAD)
definition of O_SYNC.)


The fsync() function forces all currently queued I/O operations
associated with the file indicated by the file descriptor fildes to the
synchronized I/O completion state. All I/O operations are completed as
defined for synchronized I/O file integrity completion.

RETURN VALUES

Upon successful completion, 0 is returned. Otherwise, -1 is returned and
errno is set to indicate the error. If the fsync() function fails,
outstanding I/O operations are not guaranteed to have been completed.

ERRORS

The fsync() function will fail if:

EBADF
The fildes argument is not a valid file descriptor.


EINTR
A signal was caught during execution of the fsync()
function.


EIO
An I/O error occurred while reading from or writing to the
file system.


ENOSPC
There was no free space remaining on the device containing
the file.


ETIMEDOUT
Remote connection timed out. This occurs when the file is on
an NFS file system mounted with the soft option. See
mount_nfs(8).


In the event that any of the queued I/O operations fail, fsync() returns
the error conditions defined for read(2) and write(2).

USAGE

The fsync() function should be used by applications that require that a
file be in a known state. For example, an application that contains a
simple transaction facility might use fsync() to ensure that all changes
to a file or files caused by a given transaction were recorded on a
storage medium.


The manner in which the data reach the physical medium depends on both
implementation and hardware. The fsync() function returns when notified
by the device driver that the write has taken place.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+
|Standard | See standards(7). |
+--------------------+-------------------+

SEE ALSO

read(2), sync(2), write(2), fdatasync(3C), fcntl.h(3HEAD), attributes(7),
standards(7), mount_nfs(8)

February 5, 2008 FSYNC(3C)