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How to Set Up SSH Keys on Ubuntu 18.04

SSH keys let you log in to your server without typing a password. This guide shows how to make and use them.

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Tip: Ubuntu 18.04 is old software. Newer versions use the same commands.

What are SSH keys?

SSH is a safe way to control a remote computer by typing commands. An SSH key is a pair of files. One is the private key. You keep it secret on your computer, like the key to your house. The other is the public key. You place it on the server, like a lock that only your key can open. Keys are much harder to steal than passwords.

How to Set Up SSH Keys on Ubuntu 18.04

Step 1: Make the key pair on your computer

  1. Open a terminal on your own computer.
  2. Run:
ssh-keygen -t ed25519 -C "my key"

This creates a new key pair. If your system is very old and does not support this type, use ssh-keygen -t rsa -b 4096 instead.

  1. Press Enter to save in the default place.
  2. Type a passphrase when asked. A passphrase is a short password that protects the private key file. You can leave it empty, but a passphrase is safer.

Two files appear in the ~/.ssh folder: id_ed25519 (private) and id_ed25519.pub (public).

Warning: Never share the private key. Only share the file that ends in .pub.

Step 2: Copy the public key to the server

  1. Run this, with your own user name and server address from your welcome email:
ssh-copy-id username@your_server_ip

This logs in with your password once and adds your public key to the server.

  1. If ssh-copy-id is not available, copy by hand. First show the key:
cat ~/.ssh/id_ed25519.pub

This prints the public key. Copy the whole line.

  1. Log in to the server with your password.
  2. Run these commands:
mkdir -p ~/.ssh
chmod 700 ~/.ssh
nano ~/.ssh/authorized_keys

This makes the folder, protects it and opens the key list in an editor.

  1. Paste the key on a new line. Press Ctrl+O, Enter, then Ctrl+X to save.
  2. Set the file rules:
chmod 600 ~/.ssh/authorized_keys

This lets only you read and write the file.

Step 3: Test the login

ssh username@your_server_ip

You should enter without a server password. You may need the key passphrase.

Step 4: Turn off password login (optional)

Warning: Do this only after you have tested the key. Keep one session open in case of a mistake, so you cannot lock yourself out.
  1. Open the SSH settings file:
sudo nano /etc/ssh/sshd_config
  1. Set PasswordAuthentication no.
  2. Restart SSH:
sudo systemctl restart ssh

This applies the new setting. If you need help, open a support ticket.

Quick recap

  • A key pair has a private and a public part.
  • Create it with ssh-keygen.
  • Copy the public key with ssh-copy-id.
  • Test before turning off passwords.