di server1:
ssh-keygen -t rsa
scp ~/.ssh/id_rsa.pub user@server2:~/.ssh/id_rsa_server1.pub
di server2:
cd ~/.ssh
cat id_rsa_server1.pub >> authorized_keys2
rm id_rsa_server1.pub

ssh-keygen -t rsa
scp ~/.ssh/id_rsa.pub user@server2:~/.ssh/id_rsa_server1.pub
di server2:
cd ~/.ssh
cat id_rsa_server1.pub >> authorized_keys2
rm id_rsa_server1.pub

