fsync(2)							      fsync(2)

NAME    [Toc]    [Back]

     fsync, fdatasync -	synchronize a file's in-memory state with that on the
     physical medium

SYNOPSIS    [Toc]    [Back]

     #include <unistd.h>

     int fsync(int fildes);
     int fdatasync(int fildes);

DESCRIPTION    [Toc]    [Back]

     fsync moves all modified data and attributes of fildes to a storage
     device.  When fsync returns, all in-memory	modified copies	of buffers
     associated	with fildes have been written to the physical medium.  fsync
     is	different from sync, which schedules disk I/O for all files but
     returns before the	I/O completes.

     fsync should be used by programs that require that	a file be in a known
     state.  For example, a program that contains a simple transaction
     facility might use	fsync to ensure	that all changes to a file or files
     caused by a given transaction were	recorded on a storage medium.

     fdatasync is the same as  fsync, except that it only moves	all the
     modified data, and	not the	attributes of fildes to	a storage device.

     fsync  and	fdatasync fail if one or more of the following are true:

     EBADF	    fildes is not a valid file descriptor open for writing.

     ENOLINK	    fildes is on a remote machine and the link on that machine
		    is no longer active.

     EINTR	    A signal was caught	during execution of the	system call.

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

     EINVAL	    fildes is not a valid descriptor Synchronized I/O.

DIAGNOSTICS    [Toc]    [Back]

     Upon successful completion, a value of 0 is returned. Otherwise, a	value
     of	-1 is returned and errno is set	to indicate the	error.

NOTES    [Toc]    [Back]

     The way the data reach the	physical medium	depends	on both	implementation
     and hardware.  fsync returns when the device driver tells it that the
     write has taken place.

SEE ALSO    [Toc]    [Back]

     sync(2)


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