When you
ssh <machine>, that machine is added to
.ssh/known_hosts in whatever your home directory is when you connect. This happens on every machine when it first connects with
ssh to another machine. If you want to connect without a password to a given machine, you need to, in every user home directory that will be connecting to every machine, generate a public and private key with
ssh-keygen. For example, if you're using rsa, you would generate the public-private keys with
ssh-keygen -b 1024 -t rsa
and you'll have two files in
.ssh: id_rsa and
id_rsa.pub. You copy the
id_rsa.pub file to the
authorized_keys file on all the other machines that will connect to this one as this user; that is, you'll have one entry for every machine on your network in
known_hosts and one entry for every machine on your network in
authorized_keys (you don't put the
id_rsa.pub file into the
authorized_keys on "this" machine, only those files from "other" machines).
You said above that you copied the
id_rsa file to another box? If you actually did that, you need to redo as above (copy
id_rsa.pub not
id_rsa).
Hope this helps.