KerbyServer

Since I keep having to refer to the BackupPC FAQ for these steps, here is a concise list of steps to configure ssh keys on the client and server BackupPC systems:

On the client:
Log in as root
Generate the ssh key (remember to NOT set a password):
ssh-keygen -t rsa
touch ~/.ssh/authorized_keys2
Edit ~/.ssh/authorized_keys2 and add the BackupPC public key.
Pre-pend the key with from="kerbsfedora.kerbyserver.net" to restrict access.

On the BackupPC server:
Log in as backuppc
Edit ~/.ssh/authorized_keys2 and add the client's root public key.
Pre-pend the key with from="clientHostName.kerbyserver.net" to restrict access.

Test the setup by running:
ssh -l root clientHostName whoami as backuppc on the server,
and:
ssh -l backuppc kerbsfedora whoami as root on the client.

If that fails, check permissions and repair with: chmod -R go-rwx ~/.ssh