SSH Hostbased Auth

Put this in the blog because its hard to find on the web, and if you
need to do it, it is quite critical to know it.

REPRODUCE
on cent4gardenhub
1. ssh-add -D
2. ssh -v cent5gardnenhub = asks for password. Gosh no. Not. Again.

DIAGNOSE
Q1: Is one of these false?
A. Is the result of $(hostname) the same as forward and reverse DNS
maps:
if test "$(hostname)." == "$(host $(hostname -i) | awk '{print $5}')";
then echo ok; fi
B. is $(hostname) listed in /etc/ssh/shosts.equiv on remote machine
C. is the remotehost on the ssh command line ($argv) listed in
/etc/ssh/ssh_known_hosts on the remote machine?
D. Does the public key from (C) match that listed in
ssh_host_rsa_key.pub on the local machine?
Q2: Are there any errors in /var/log/authpriv on the remote machine?