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.

fdatasync — synchronize the data of a file (REALTIME)

#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.

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.


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().



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

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

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

2017 IEEE/The Open Group