Login to Ubuntu Remote Server - Passwordless via SSH Only

To make SSH passwordless and allow only key-based authentication (no password authentication), you'll need to perform the following steps:

1. Generate an SSH Key Pair (if not already done):

If you haven't already generated an SSH key pair, you can do so with the following command on your local machine:

   ssh-keygen -t rsa -b 4096

This will create an SSH key pair in your ~/.ssh directory, typically named id_rsa (private key) and id_rsa.pub (public key).

1. Copy the Public Key to the Remote Server:

Use the ssh-copy-id command to copy your public key to the remote server. Replace username with your username on the remote server and remote_server_ip with the server's IP address or hostname:

   ssh-copy-id -i ~/.ssh/id_rsa.pub username@remote_server_ip

You'll be prompted to enter your remote server password for this step.

1. Disable Password Authentication on the Remote Server:

To ensure that only key-based authentication is allowed, you should disable password authentication on the remote server. Edit the SSH server configuration file on the remote server with a text editor. You can use nano, vim, or any text editor you prefer:

   sudo nano /etc/ssh/sshd_config

Find the following line:

   #PasswordAuthentication yes

Uncomment it (remove the #) and change it to:

   PasswordAuthentication no

Save and exit the text editor.

1. Restart the SSH Service:

To apply the changes, restart the SSH service on the remote server:

   sudo systemctl restart ssh

1. Test SSH Login:

Try to SSH into the remote server from your local machine. It should now only allow key-based authentication and not prompt for a password:

   ssh username@remote_server_ip

You should be able to log in without a password.

By following these steps, you've configured SSH to allow only key-based authentication and disabled password authentication on the remote server, making SSH passwordless for your login sessions.