Command to send public key to remote host

You might be looking for this command:

cat ~/.ssh/id_rsa.pub | ssh user@hostname 'cat >> .ssh/authorized_keys'

It appends your public key to the servers authorized keys.

Source

If your server is already set up to not accept password-based login, you might get a Permission denied (publickey) error.

This is another method to send the key, using netcat, so you don't have to authenticate. It will only work over a local network, but you can use port forwarding to do this over the internet.

On the server:

$ nc -l 55555 >> ~/.ssh/authorized_keys

On the client (replace HOSTNAME with the hostname or IP of the server):

$ nc HOSTNAME 55555 < ~/.ssh/id_rsa.pub

You can replace 55555 with an open port of your choice.

source: chat over lan from linux to linux?

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Appendix for total newbies: I don't think anyone's mentioned this yet, but if you get ERROR: failed to open ID file '/home/username/.pub': No such file, you need to generate a key first. The Ubuntu help pages have a great guide on Generating RSA Keys.

You are looking for ssh-copy-id. All this command does is create .ssh and .ssh/authorized_keys and set their permissions appropriately if they don't exist. Then it appends your public key to the end of .ssh/authorized_keys.