sftp -i /var/id_rsa_test user@host
The authenticity of host '[host]:22 ([xx.xx.xx.xx]:22)' can't be established.
DSA key fingerprint is e1:e2:29:c4:30:9a:8c:de:3f:3d:97:cd:6d:dd:6f:e5.
Are you sure you want to continue connecting (yes/no)?

ssh-keyscan host >> ~/.ssh/known_hosts