Fetching SSH hostkeys without interaction

Applies at least to openssh.

To get the hostkeys for a server, and write them to known_hosts-file (to avoid that yes/no query when the key isn't known), you can do:

ssh-keyscan -t rsa foo foo.example.com 1.2.3.4 >> ~/.ssh/known_host

This example queries the hostkeys for the very same machine, but under 3 different "names" (hostname, FQDN, IP) and redirects the output to the known_hosts-file.

Notes:

• if done blindly, the known_host-file may grow very large. It might be wise to check for key existance first
• if multiple keys for the same host exist in known_hosts, the first one is taken (which might be an old or wrong one)