Adding ssh keys to a new server without having previously set up users on that server
- How can I use ssh-copy-id to copy my public key to the server if I haven't setup a user yet?
You'd need the password for the user, and for SSH to accept passwords (not always the case). I wouldn't expect this to be the way forward in this sort of situation, where the VPS provider has a copy of your public key.
- What is the default root password on the server? How Would I find this out? I've tried ubuntu, root, the basics.
There's nothing guaranteed; it will be defined by the VPS provider, and should be in their documentation.
- What does adding a public key via GUI on the server host's website normally do with regards to server users? Does it add the key to the known_hosts file?
Close; it would add it to the .ssh/authorized_keys file in some users' home directory. As you've identified, knowing which user is opaque
- What is the technical significance of the final comment line in my public ssh key, currently [email protected]?
Nothing technical, it's just a label for human use.