When you use ssh to connect to a remote host for the first time you will be confronted with a message like:
The authenticity of host 'rosz (192.168.1.2)' can't be established. RSA key fingerprint is 99:1f:eb:c2:8f:cb7:33:23:1f:4c:e5:51:20:e9:85:5a. Are you sure you want to continue connecting (yes/no)?
SSH does not know this host. Type yes to add the fingerprint of this host to /.ssh/known_hosts. Next time you connect to this remote host you should not get this message.