hard link to directories

[Heinz-Josef Claes]

Hi,

the man page of the ln command
(ln (coreutils) 5.0    March 2003   LN(1))
says:


   -d, -F, --directory
          hard link directories (super-user only)

I tried to do this:

# mkdir a
# ln -F a b
ln: creating hard link `b' to `a': Operation not permitted

I tried this in /dev/shm, on ext2 and on reiserfs3.6. It never was
possible. Is this a theoretical feature or a real one?
I tested it with SuSE8.2 (kernel 2.4.20) and SuSE9.0 (kernel 2.4.21).

I'm really interested in this feature, because I've write a backup tool
(see below) which is based on recognising the *contents* of files. Every
content is only one time in the whole backup; making the files appear at
the appropriate place is done via hard links. If I could link
directories, I would be able to improve this by making only a hard link
to a (sub-)directory if nothing has changed in it.

Best regards,

-- 
Heinz-Josef Claes                     address@hidden
project: http://sourceforge.net/projects/storebackup
      -> snapshot-like backup to another disk