How do I allow empty passwords?

[Eric Hanchrow <offby1@blarg.net>]

I've installed a test system, on which there is absolutely no
important information.  So for my own convenience, I'd like to be able
to make my root password empty.  I realize that on a production
machine, this would not be a great idea.

The system that I installed is the latest version of potato that has
made it to whichever mirror I rsync from ... which is to say that I
can't say precisely which version I'm using, but it's as up-to-date as
I know how to make it.  (If anyone actually wants to know which
versions of various packages I've got installed, I'd naturally be
happy to provide that information).

When I installed the system, I of course was asked for a root
password.  I used `bob', since it's easy to remember and type.

I later tried to change it to be empty, like this:

        # passwd
        Enter new UNIX password:                (here I just hit the Enter key)
        Retype new UNIX password:               (again, I just hit Enter)
        No password supplied
        Enter new UNIX password:                (here I just hit the Enter key)
        Retype new UNIX password:               (again, I just hit Enter)
        No password supplied
        Enter new UNIX password:                (here I just hit the Enter key)
        Retype new UNIX password:               (again, I just hit Enter)
        No password supplied
        passwd: Authentication token manipulation error

Now, I assume that this behavior isn't due to a bug, but rather to a
policy: passwords apparently have to be some minimum length.  That's
fine, but I'd like to change the policy, and can't quite figure out
how.

Now, I see in /etc/pam.d/passwd a line like this:

    password   required   pam_unix.so nullok obscure min=4 max=8

I wonder if `min=4' means that the password must be four characters
long (although if that's the case, I wonder why I got away with using
`bob').  In any case, I haven't been able to find any documentation
for the arguments `nullok obscure min=4 max=8'.  `man pam.d' tells me
to look at the "Linux-PAM system administrators' guide", which doesn't
answer my question, and which doesn't appear to be part of any Debian
package (that's annoying -- the Man page refers me to it, but it isn't
included with Debian).

Anyway: how do I do it?  And in general, where do I find the
documentation with which I could have answered the question myself?

Thanks

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