rm -W

[GlowingApple]

Hi, does anyone know how the -W flag works for rm? The man page specifies:

Attempt to undelete the named files.  Currently, this option can only be used to recover files covered by whiteouts.

I'm not quite sure what they mean by whiteout since rm only unlinks the file (unless the -P flag is used and then it's written out three times, so I doubt any simple software method could recover the file). I don't know of any way to have rm perform a whiteout, and I don't know of any command line tools that do.

When I create a file, rm it, and then try to rm -W it I get a "No such file or directory" error. If I attempt it on an already existant file, I get a "File exists" error.

Is this an option that's available in other systems but not in Mac or am I misunderstanding it's purpose/use?

[hayne]

I believe that the "-W" flag only applies when a filesystem has been mounted as a layer over another one using a "union" mount. (This is highly unusual and I don't think you'll see it in normal OS X use.)
Here's an article on union mounts: http://www.usenix.org/publications/l...ers/mckusick.a
It explains the "whiteout" operation.