The public-key authentication method requires you to copy your public SSH key to the server's authorized_keys file. The authorized_keys file is in the ~/.ssh/ directory of the user you are connecting.
Copying your public key to the file will allow you to log in to the server using the public-key authentication method, enabling passwordless SSH login. If your key pair is not protected by a passphrase, it could further be used to perform some automation tasks that include remotely executing commands via a script.
Your public key could be copied manually or using ssh-copy-id tool. There are also some SSH tricks to copy your SSH key to the server.
$ ls ~/.ssh/id* /home/user/.ssh/id_rsa /home/user/.ssh/id_rsa.pub
The public key is normally the one with the .pub extension.
$ file .ssh/id_rsa.pub .ssh/id_rsa.pub: OpenSSH RSA public key
authorized_keys file accepts public keys in OpenSSH format.
$ ssh-copy-id user@remote-host The authenticity of host 'remote-host (192.168.111.135)' can't be established. ECDSA key fingerprint is SHA256:hXGpY0ALjXvDUDF1cDs2N8WRO9SuJZ/lfq+9q99BPV0. Are you sure you want to continue connecting (yes/no)? yes /usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed /usr/bin/ssh-copy-id: INFO: 2 key(s) remain to be installed -- if you are prompted now it is to install the new keys user@remote-host's password: Number of key(s) added: 2 Now try logging into the machine, with: "ssh 'user@remote-host'" and check to make sure that only the key(s) you wanted were added.
If you want to use other public key rather that then one in the default location, use the -i option.
$ ssh-copy-id -i ~/.ssh/other_key.pub user@remote-host
$ ssh -i .ssh/id_rsa user@remote-host Welcome to Ubuntu 19.04 (GNU/Linux 5.0.0-20-generic x86_64) * Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantage System information as of Sat Jun 29 11:31:23 UTC 2019 System load: 0.16 Processes: 211 Usage of /: 25.8% of 19.56GB Users logged in: 1 Memory usage: 13% IP address for ens33: 192.168.111.135 Swap usage: 0% * MicroK8s 1.15 is out! It has already been installed on more than 14 different distros. Guess which ones? https://snapcraft.io/microk8s 0 updates can be installed immediately. 0 of these updates are security updates. Last login: Sat Jun 29 11:08:20 2019 from 192.168.111.1
$ cat ~/.ssh/id_rsa.pub | ssh user@remote-host 'cat >> ~/.ssh/authorized_keys'
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