bsd man page for fsync

FSYNC(2)							System Calls Manual							  FSYNC(2)

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

SYNOPSIS
       fsync(fd)
       int fd;

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 modi-
       fied 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.

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

ERRORS
       The fsync fails 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.

SEE ALSO
       sync(2), sync(8), update(8)

4.2 Berkeley Distribution					   May 22, 1986 							  FSYNC(2)