Home Assistant, Docker, and using SSH

A common problem that comes up with people using one of the Supervisor based install methods, or Docker, is that when they try to use ssh it fails, yet when testing it works.

What. The. Heck?

Well, you’ve hit two problems because of Docker - all your testing was done in a different container.

1. You need to accept the remote host’s key. The default is to prompt the human, and you don’t see that.
2. You need to provide the location private key, since it’s not where SSH is looking for it.

Solving this is simple enough.

Copy the key(s)

First thing to do is to copy the private key into your config folder. I’d recommend that you put it in a sub-folder, and exclude that from any git push. For example, create /config/ssh and copy your private key (typically id_ed25519 or id_rsa) there.

Oh, and that private key, it needs to have no passphrase since you won’t be able to enter it.

If you created a fresh key, don’t forget to add the public key to the authorized_keys file on server you’re connecting to. One way of doing that is to use the ssh-copy-id command, eg:

ssh-copy-id -i ~/.ssh/id_ed25519.pub [email protected]

Tell SSH to accept new host keys

This is easy, there’s an option to tell the SSH client to accept new keys. This is safer than the old option to just blindly accept all keys. To do this you add StrictHostKeyChecking=accept-new to your SSH options.

All together now

What does this mean? It means where you currently have ssh you’d instead have:

ssh -i /config/ssh/id_ed25519 -o StrictHostKeyChecking=accept-new

For example your full command may be:

ssh -i /config/ssh/id_ed25519 -o StrictHostKeyChecking=accept-new [email protected] /usr/sbin/meltdown

Now it’ll use that key, and accept new keys without prompting. It won’t accept keys that change, which is a good security feature.