ssh public key authentication

[Luca Ferrari]

Hi,
I'd like a user to ssh another host (both ubuntu 8.1) without being prompted 
for a password, so I copied the rsa (and also dsa) public keys to the target 
host, added these keys to the authorized_keys file but when I do ssh I'm 
prompted for a password, and I don't understand why. Here's an excerpet of the 
debug messages of the ssh client:

debug1: Next authentication method: publickey
debug1: Trying private key: /var/backups/.ssh/identity
debug3: no such identity: /var/backups/.ssh/identity
debug1: Offering public key: /var/backups/.ssh/id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: publickey,password
debug1: Offering public key: /var/backups/.ssh/id_dsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: publickey,password
debug2: we did not send a packet, disable method
debug3: authmethod_lookup password
debug3: remaining preferred: ,password
debug3: authmethod_is_enabled password


anyone has an idea of what the problem could be?

Thanks,
Luca