fsync,  fdatasync  -  synchronize  a  file's in-core state with storage


   #include <unistd.h>

   int fsync(int fd);

   int fdatasync(int fd);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       Glibc 2.16 and later:
           No feature test macros need be defined
       Glibc up to and including 2.15:
               || /* since glibc 2.8: */ _POSIX_C_SOURCE >= 200112L
       _POSIX_C_SOURCE >= 199309L || _XOPEN_SOURCE >= 500


   fsync() transfers ("flushes")  all  modified  in-core  data  of  (i.e.,
   modified  buffer  cache  pages  for)  the  file referred to by the file
   descriptor fd to the disk device (or other permanent storage device) so
   that  all  changed  information  can be retrieved even after the system
   crashed or was rebooted.  This includes writing through or  flushing  a
   disk  cache  if present.  The call blocks until the device reports that
   the transfer has  completed.   It  also  flushes  metadata  information
   associated with the file (see stat(2)).

   Calling  fsync()  does  not  necessarily  ensure  that the entry in the
   directory containing the file has  also  reached  disk.   For  that  an
   explicit fsync() on a file descriptor for the directory is also needed.

   fdatasync() is similar to fsync(), but does not flush modified metadata
   unless that metadata is needed in order  to  allow  a  subsequent  data
   retrieval to be correctly handled.  For example, changes to st_atime or
   st_mtime  (respectively,  time  of  last  access  and  time   of   last
   modification; see stat(2)) do not require flushing because they are not
   necessary for a subsequent data read to be handled correctly.   On  the
   other  hand,  a  change  to  the  file  size  (st_size,  as made by say
   ftruncate(2)), would require a metadata flush.

   The aim of fdatasync() is to reduce disk activity for applications that
   do not require all metadata to be synchronized with the disk.


   On  success, these system calls return zero.  On error, -1 is returned,
   and errno is set appropriately.


   EBADF  fd is not a valid open file descriptor.

   EIO    An error occurred during synchronization.

          fd is bound to a special file (e.g., a pipe,  FIFO,  or  socket)
          which does not support synchronization.


   POSIX.1-2001, POSIX.1-2008, 4.3BSD.


   On    POSIX    systems    on    which    fdatasync()    is   available,
   _POSIX_SYNCHRONIZED_IO is defined in <unistd.h> to a value greater than
   0.  (See also sysconf(3).)


   On  some  UNIX  systems  (but  not  Linux),  fd must be a writable file

   In Linux 2.2 and earlier, fdatasync() is equivalent to fsync(), and  so
   has no performance advantage.

   The   fsync()   implementations   in  older  kernels  and  lesser  used
   filesystems does not know how to flush disk  caches.   In  these  cases
   disk  caches  need  to  be  disabled  using  hdparm(8)  or sdparm(8) to
   guarantee safe operation.


   sync(1), bdflush(2), open(2), pwritev(2), sync(2),  sync_file_range(2),
   fflush(3), fileno(3), hdparm(8), mount(8)


   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.