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FSYNC(2)                      System Calls Manual                     FSYNC(2)

NAME
     fsync, fsync_range -- synchronize a file's in-core state with that on
     disk

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <&lt;unistd.h>&gt;

     int
     fsync(int fd);

     int
     fsync_range(int fd, int how, off_t start, off_t length);

DESCRIPTION
     fsync() causes all modified data and attributes of fd to be moved to a
     permanent storage device.  This normally results in all in-core modified
     copies of buffers for the associated file to be written to a disk.

     fsync() should be used by programs that require a file to be in a known
     state, for example, in building a simple transaction facility.

     fsync_range() causes all modified data starting at start for length
     length of fd to be written to permanent storage.  Note that fsync_range()
     requires that the file fd must be open for writing.

     fsync_range() may flush the file data in one of two manners:

           FDATASYNC  Synchronize the file data and sufficient meta-data to
                      retrieve the data for the specified range.

           FFILESYNC  Synchronize all modified file data and meta-data for the
                      specified range.

     By default, fsync_range() does not flush disk caches, assuming that
     storage media are able to ensure completed writes are transfered to
     media.  The FDISKSYNC flag may be included in the how parameter to
     trigger flushing of all disk caches for the file.

     If the length parameter is zero, fsync_range() will synchronize all of
     the file data.

RETURN VALUES
     A 0 value is returned on success.  A -1 value indicates an error.

ERRORS
     fsync() or fsync_range() fail if:

     [EBADF]            fd is not a valid descriptor.

     [EINVAL]           fd refers to a socket, not to a file.

     [EIO]              An I/O error occurred while reading from or writing to
                        the file system.

     Additionally, fsync_range() fails if:

     [EBADF]            fd is not open for writing.

     [EINVAL]           start + length is less than start.

NOTES
     For optimal efficiency, the fsync_range() call requires that the file
     system containing the file referenced by fd support partial
     synchronization of file data.  For file systems which do not support
     partial synchronization, the entire file will be synchronized and the
     call will be the equivalent of calling fsync().

SEE ALSO
     sync(2), sync(8)

HISTORY
     The fsync() function call appeared in 4.2BSD.

     The fsync_range() function call first appeared in NetBSD 2.0 and is
     modeled after the function available in AIX.

NetBSD 6.1.5                     May 17, 2010                     NetBSD 6.1.5