FSYNC(3C) Standard C Library Functions FSYNC(3C)
fsync - synchronize changes to a file
#include <unistd.h>
int fsync(int fildes);
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.
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.
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).
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.
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). |
+--------------------+-------------------+
read(2), sync(2), write(2), fdatasync(3C), fcntl.h(3HEAD),
attributes(7), standards(7), mount_nfs(8)
February 5, 2008 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)