password file recovery question

[doug at allensystemconsultants.com]

I've got a possibly silly question and I believe I have an answer, but
I want to see if what I think is the answer is feasible.

I've had to rebuild a mail server from scratch, upgrading from
4.6-STABLE to 4.8-STABLE in the process.  The other mail server had
crashed, with disk errors so sever it wouldn't fsck clean.  I was able
to get it together enough to pull my configuration files off the old
server.  I was even able to get the master.passwd file off of it.

When I rebuilt, I added users one at a time, so directories, etc. were
there.  But then I copied the master.passwd file from the previous
server over the new master.passwd file and most of the passwords were
scrambled.  Is it impossible to use the old master.passwd file when
picking up the pieces of the old server on the new server?  If it
isn't impossible, under what conditions can one reuse the file
contents?  

I had all the UID's and GID's identical when I entered users, so that
isn't the problem.  I'm wondering if it's the hashing of the password
that is the problem?  Different system, different key and seed,
different hash results for the same string of characters, so the
passwords are scrambled for most users.  If I could keep the keys and
the hashes identical, then the passwords wouldn't get scrambled is one
idea I've had running around.  It wouldn't be an issue, except that I
have about 1000 users and not all of them are good about getting back
to me on issues.

I did notice that if I already have passwords set before I copy the
master.passwd file over, those users seem to retain the password set
when I created them with adduser.  So my password, another user who
helps me test, and root weren't scrambled.

Thanks for any information you may be able to provide.

Doug Allen

Doug Allen
Allen System Consultants