Path: utzoo!attcan!uunet!mcsun!hp4nl!phigate!ehviea!leo
From: leo@ehviea.ine.philips.nl (Leo de Wit)
Newsgroups: comp.unix.wizards
Subject: Re: Hard links to directories: why not?
Keywords: ln, directories, security...
Message-ID: <835@ehviea.ine.philips.nl>
Date: 19 Jul 90 12:45:24 GMT
References: <5222@milton.u.washington.edu> <6940@eos.UUCP>
Reply-To: leo@ehviea.UUCP (Leo de Wit)
Organization: Philips I&E Eindhoven
Lines: 31

In article <6940@eos.UUCP> jbm@eos.UUCP (Jeffrey Mulligan) writes:
|wiml@milton.u.washington.edu (William Lewis) writes:
|
|>   In the man entry for ln(1) (and for link(2)),  it says that
|>hard links may not be made to directories, unless the linker is
|>the super-user (in order to make '.' and '..', I suppose). My 
|>question is: why not?
|
|What should be the output of the last command of this sequence?
|
|mkdir dir1
|mkdir dir2
|mkdir dir1/a_directory

a_directory contains entries '.' and '..' that point to itself
and its parent, dir1, respectively.

|ln dir1/a_directroy dir2/directory_link
|cd dir2/directory_link
|cd ..
|pwd

If you shell is csh, it could perhaps tell you "dir2". That's because
csh has 'pwd' builtin and keeps track of the current directory itself
in $cwd; it is also confused by symbolic links *). But a proper pwd
(try /bin/pwd) should always give you "dir1" (as absolute path, of
course), since that is where '..' points at.

    Leo.

*) This behaviour of C shell is corrected in more recent versions.