freebsd man page for fsync

FSYNC(2)						      BSD System Calls Manual							  FSYNC(2)

NAME
     fsync -- synchronise changes to a file

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     int
     fsync(int fd);

DESCRIPTION
     The fsync() system call 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.

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

RETURN VALUES
     The fsync() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate
     the error.

ERRORS
     The fsync() fails if:

     [EBADF]		The fd argument is not a valid descriptor.

     [EINVAL]		The fd argument 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), syncer(4), sync(8)

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

BSD
								   June 4, 1993 							       BSD