rsync-ssh problem

[Paul Trevethan]

I am having a real nightmare getting automated login with ssh to work;
hoping someone can guide me. I am running Ubuntu 6.10.

I have a main machine (called greywolf) which has a partition for
my /home on it. I am doing backups to an extrnal usb drive attached to
a Linksys NSLU2 (called slug) running UnSlung firmware. All hosts,
networking, shares, firewall & such stuff is working fine. Currently I
use this command on greywolf to push-backup some key files to the
external drive:

rsync -avz --delete --numeric-ids /home/paul/somefiles -e ssh
paul at slug:/backup/edgy

I get asked for paul´s password on slug and away it goes. Works like a
charm creating ´somefiles´ on slug. I want to automate this process
through cron so, I worked out I have to get ssh working automatically
and without password. I gathered a few howtos etc from around the web
and settled on the commands below to set it up:

on greywolf - $ssh-keygen -t dsa ; put the file in /home/paul/.ssh,
answered passphrase with <enter> only.

then I copied the .pub key to slug, appending it to user paul´s
authorized_keys file. I used the command:

$cat ~/.ssh/id_dsa.pub | ssh paul at slug ¨cat- >> ~/.ssh/authorized_keys¨

Now, interestingly, I did this in reverse as well. i.e. I opened a
session on slug with Putty and generated the keys and sent them to my
home on greywolf. I mention this because here is my problem and dilema?!

If I start on slug (in a Putty ssh session) I can type $ssh
paul at greywolf and it works just fine, no passwords, just a command
prompt on greywolf. Just what I expect.

However, it does not work the other way, which is what I want for the
backups to be automated. If I type ssh paul at slug from command prompt on
greywolf, it insists on still asking for paul´s password on slug before
making the connection. I am quite perplexed as to why it works in one
direction and not the other.

I was wondering whether I should try rsa keys instead, but this way
works from slug to greywolf?

I have even done a diff on the ssh_config and sshd_config files from
each location and I cannot see an obvious problem to cause this. I
would appreciate advice on further tests I might conduct to debug this
or a solution even?!

Paul.