This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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().

       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 .

IEEE/The Open Group                                   2017                                     FDATASYNC(3POSIX)

       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.

       The fdatasync() function shall fail if:

       EBADF  The fildes argument is not a valid file descriptor.

       EINVAL 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().

       Thefollowingsectionsareinformative.

       None.

       None.

       fdatasync — 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.

       None.

       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.

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

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

       #include <unistd.h>

       int fdatasync(int fildes);