fdatasync - Man Page

synchronize the data of a file (REALTIME)


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <unistd.h>

int fdatasync(int fildes);


The fdatasync() function shall force all currently queued I/O operations associated with the file indicated by file descriptor fildes to the synchronized I/O completion state.

The functionality shall be equivalent to fsync() with the symbol _POSIX_SYNCHRONIZED_IO defined, with the exception that all I/O operations shall be completed as defined for synchronized I/O data integrity completion.

Return Value

If successful, the fdatasync() function shall return the value 0; otherwise, the function shall return the value -1 and set errno to indicate the error. If the fdatasync() function fails, outstanding I/O operations are not guaranteed to have been completed.


The fdatasync() function shall fail if:


The fildes argument is not a valid file descriptor.


This implementation does not support synchronized I/O for this file.

In the event that any of the queued I/O operations fail, fdatasync() shall return the error conditions defined for read() and write().

The following sections are informative.



Application Usage

Note that even if the file descriptor is not open for writing, if there are any pending write requests on the underlying file, then that I/O will be completed prior to the return of fdatasync().



Future Directions


See Also

aio_fsync(), fcntl(), fsync(), open(), read(), write()

The Base Definitions volume of POSIX.1-2017, <unistd.h>

Referenced By

aio_fsync(3p), unistd.h(0p).

2017 IEEE/The Open Group POSIX Programmer's Manual