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Say I have two computers connected to the same Wifi network. Let's call them computer-A & computer-B.

I am using computer-A, I can ping computer-B without issues.

Now, on computer-A, I have generated a new SSH key pair (but not the default id_rsa pair which this computer already have). Let's call the keys : newkey and newkey.pub.

I would like to use ssh-copy-id command to copy the newkey.pub to computer-B.

I get confused at this point, in order to do above thing, does computer-B need to have a previously generated public key of keypair from computer-A in order to establish a SSH connection for the ssh-copy-id to work?

Asking in another way, if computer-B doesn't have any public key at all from computer-A, would ssh-copy-id still work?

I checked this ssh-copy-id doc, I wonder in their example ssh-copy-id -i ~/.ssh/mykey user@host, is that ~/.ssh/mykey a public key or private key?

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ssh-copy-id uses ssh for connecting. So if there is a key available already, it will use that (in case of multiple identity files). If there is no key, it will ask for a password.

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  • Could you please be more specific? When you say "if there is a key available already", which key? (the public or private one)? available in where? (computer-A or computer-B) in my case?
    – user842225
    Feb 9 at 13:35
  • I mainly want to understand if computer-B doesn't have any key, would ssh-copy-id still work on computer-A to move key to computer-B
    – user842225
    Feb 9 at 13:36
  • ssh-copy-id will behave exactly as if ssh would if you issued the ssh computer-B command on computer-A. If ssh asks for a password, so will ssh-copy-id. If it isn't, ssh-copy-id won't either.
    – Lacek
    Feb 9 at 14:26
  • This is exactly what confused me, if it is like that, why I see people use ssh-copy-id for copy public key to another machine in order to establish SSH connection, if using ssh-copy-id is same as using ssh it would mean the public key should already in place of the remote machine before using ssh-copy-id. Your answer still makes it like a "chicken-egg which one first" confusion to me... I wish I could get an answer explain the point of using ssh-copy-id to move public key to another machine for establish SSH connection... I hope you understand the confusion I am having now.
    – user842225
    Feb 9 at 14:53
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    Yes, you use password or whatever else is configured once. If key-based auth enabled and ssh-copy-id succeeds, you may start using key-based authentication.
    – Nikita Kipriyanov
    Feb 9 at 15:13

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