Ubuntu SSH Key Authentication and Basic Hardening

SSH key authentication is more secure and more convenient than passwords. This guide covers importing or adding your public key, disabling password login, and optional quality-of-life tweaks for Ubuntu servers.

Add your SSH public key to Ubuntu

You have two options for getting your public key onto the server.

ssh-import-id gh:<username>

pip install ssh-import-id

mkdir -p ~/.ssh
chmod 700 ~/.ssh
echo "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAA... user@host" >> ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys

Disable password authentication

Edit the SSH config to reject password-based logins:

sudo nano /etc/ssh/sshd_config.d/50-cloud-init.conf

Set (or uncomment) the following line:

PasswordAuthentication no

Then reload and restart SSH:

sudo systemctl daemon-reload
sudo systemctl restart ssh.service

Passwordless sudo Optional

Since you’re already authenticating with SSH keys, you can skip the password prompt for sudo. Replace <username> with your actual username:

echo "<username> ALL=(ALL) NOPASSWD: ALL" | sudo EDITOR=tee visudo -f /etc/sudoers.d/<username> >/dev/null

Install QEMU Guest Agent (Proxmox VMs) Optional

If this is a Proxmox VM, install and enable the guest agent for proper shutdown signaling and IP reporting:

sudo apt update
sudo apt install qemu-guest-agent -y
sudo systemctl enable qemu-guest-agent
sudo systemctl start qemu-guest-agent

You now have a base configuration for your Ubuntu install. You can use this VM as is or read the following article to configure a template for future use.