Re: "cannot dereference" error from "chown -RH"

[Jim Meyering]

enh wrote:

> if i create a dangling symbolic link within a tree, "chown -RH
> top-of-tree" gets me a "cannot dereference" error.
>
> STEPS TO REPRODUCE:
>
>   cd /tmp
>   mkdir chown-test
>   cd chown-test
>   ln -s poop parp
>   cd ..
>   chown -RH :nogroup chown-test

Thanks for taking the time to report that.
However, I think you have a misunderstanding.

> ACTUAL OUTPUT:
>
>   chown: cannot dereference `chown-test/parp': No such file or directory
>   chown: changing group of `chown-test': Operation not permitted
>
> EXPECTED BEHAVIOR:
>
> i don't think chown should try to dereference the dangling symbolic link.

You're confusing the hierarchy-traversal options (-H, -L, -P, and whether
they dereference symlinks) and an independent option that determines,
once a file system object has been selected, whether chown should
operate on it or on whatever it references if it's a symlink.

Maybe you didn't notice the description of the --dereference option?

       --dereference
              affect the referent of each symbolic  link  (this  is  the
              default), rather than the symbolic link itself

       -h, --no-dereference
              affect  each  symbolic link instead of any referenced file
              (useful only on systems that can change the ownership of a
              symlink)

> looking at the source, i think affect_symlink_referent should be
> false. i think the code in chown.c's main() should be more like the
> code in chcon.c's main(), but that both should be changed to test
> (bit_flags & FTS_PHYSICAL) rather than (bit_flags == FTS_PHYSICAL),
> because -H sets bit_flags to FTS_COMFOLLOW | FTS_PHYSICAL.
>
> alternatively, i could have completely misunderstood the intended
> behavior of -RH. but it seems to me like -H should cause only symbolic
> links explicitly named on the command-line to be dereferenced.

This is described in the "info" documentation,
i.e., what you get when you run "info coreutils chown".
If that's not clear enough, specific suggestions for improvement
are most welcome.

It cross-references this section:

2.9 Traversing symlinks
=======================

The following options modify how `chown' and `chgrp' traverse a
hierarchy when the `--recursive' (`-R') option is also specified.  If
more than one of the following options is specified, only the final one
takes effect.  These options specify whether processing a symbolic link
to a directory entails operating on just the symbolic link or on all
files in the hierarchy rooted at that directory.

   These options are independent of `--dereference' and
`--no-dereference' (`-h'), which control whether to modify a symlink or
its referent.

`-H'
     If `--recursive' (`-R') is specified and a command line argument
     is a symbolic link to a directory, traverse it.

`-L'
     In a recursive traversal, traverse every symbolic link to a
     directory that is encountered.

`-P'
     Do not traverse any symbolic links.  This is the default if none
     of `-H', `-L', or `-P' is specified.