There’s a good tool for copying ssh keys to remote host under your account: ssh-copy-id. This lets you copy your public key under your account on the remote server.

But what about other accounts? Let’s say you want to log in as root (with key-only auth method, of course)? How to copy key to root user’s .ssh/authorised_keys? One way to do it is to log as your ordinary user, make yourself root with sudo su -, open authorized_keys with editor, paste, save etc… Tedious? Yes.

That’s why there’s a good oneliner:

cat ~/.ssh/id_rsa.pub | ssh your_user@remote.server.com “sudo tee -a /root/.ssh/authorized_keys”