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Setup SSH Securely, with Password-less Login

SSH (Secure Shell) is a protocol used to securely connect to a remote computer or server over a network. It allows you to execute commands, manage files, and perform administrative tasks remotely.

Setup OpenSSH​

OpenSSH is a connectivity tool for remote sign-in that uses the SSH protocol. In this post, we will see how to set it up.

Server​

If you're setting up SSH on a Debian or Ubuntu server, you'll need to install the OpenSSH server first. Most of the time, if you purchase a VPS or a dedicated server, you will have this set up and enabled by default.

  • Update package lists:

    sudo apt update

  • Install OpenSSH server:

    sudo apt install openssh-server -y

  • Enable and start the SSH service:

    sudo systemctl enable ssh
    sudo systemctl start ssh

  • Verify that SSH is running:

    sudo systemctl status ssh

  • If you cannot connect to it, adjusting the firewall settings to allow SSH connections might fix the issue, especially on Ubuntu Server instances.

    sudo ufw allow OpenSSH
    sudo ufw enable

Client​

To connect to an OpenSSH server, you need an SSH client installed on your device.

Windows​

Windows includes a built-in OpenSSH client, but you can also use third-party tools like PuTTY, Termius, or XShell.

  1. Open Command Prompt or PowerShell.
  2. Check if OpenSSH is installed: 
    ssh -V
  3. If not installed, install it via PowerShell: 
    Add-WindowsFeature -Name OpenSSH-Client
  4. If the above command doesn't work:
    • Go to Settings → Apps → Optional Features
    • Find and install OpenSSH Client

Linux & macOS​

SSH is pre-installed on most Linux distributions and macOS versions.

To verify its installation, run:

ssh -v

If SSH is missing, install it via your package manager:

  • Debian/Ubuntu: sudo apt install openssh-client
  • Arch Linux: sudo pacman -S openssh
  • macOS (if missing): brew install openssh

Basic Guide​

Connecting via SSH​

  • Open your terminal (on macOS, Linux, or Windows via PowerShell).

  • Use the following command:

    ssh username@hostname_or_ip
    • username: The user on the remote server.
    • hostname_or_ip: The remote server’s IP address or domain name.

    For example:

    ssh hirusha@192.168.1.100

  • Authenticate: you'll be prompted to enter the password.

Setup Password-less Login​

Generate Key Pair​

Open a terminal and run:

ssh-keygen -t rsa -b 4096 -C "your_email@example.com"
  • -t rsa: Uses RSA as the algorithm.
  • -b 4096: Sets a strong 4096-bit key length.
  • -C: Adds an optional comment (like your email) for identification.

Press Enter to save it in the default location.

Two files will be generated: id_rsa, the private key, which you should not share with anyone; and id_rsa.pub, the public key. This should be added to the server. Once it's set up, you can authenticate using the matching private key of this key pair.

The default file locations are:

  • Linux: ~/.ssh/id_rsa and ~/.ssh/id_rsa.pub
  • Windows: C:\Users\%USERNAME%\.ssh\id_rsa and C:\Users\%USERNAME%\.ssh\id_rsa.pub

You can also set a passphrase for extra security (optional but recommended).

Copy the Public Key​

As mentioned above, the public key should be added to the the authorized keys of server.

Linux / MacOS​

Linux and MacOS installations of OpenSSH client also comes with the ssh-copy-id tool to make things easy for you.

ssh-copy-id -i ~/.ssh/id_rsa.pub user@remote_host

This automatically adds your public key to the server.

Windows​

The ssh-copy-id tool is not natively available on Windows, so you need to do it manually:

  1. Open your public key file in Notepad:

    notepad C:\Users\%USERNAME%\.ssh\id_rsa.pub

  2. Copy the entire content.

  3. Log in to the remote server using your password:

    ssh user@remote_host

  4. On the server, append the key to ~/.ssh/authorized_keys into a new line:

    mkdir -p ~/.ssh
    echo "your-public-key-content" >> ~/.ssh/authorized_keys
    chmod 600 ~/.ssh/authorized_keys
    chmod 700 ~/.ssh

Note that if you are setting this up for another user, either log in as that user and then run the above commands, or just ensure that you place the public key inside the .ssh/authorized_keys file in that user's home folder.

Test​

Now, try logging in:

ssh user@remote_host

If everything is set up correctly, you should log in without entering a password.

(Optional) Passphrase Setup​

If you set a passphrase, you'll have to enter it every time. To avoid that, use ssh-agent:

Linux/macOS​

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_rsa

Windows​

Start-Service ssh-agent
ssh-add C:\Users\%USERNAME%\.ssh\id_rsa

To make SSH agent start automatically on reboot:

Set-Service -Name ssh-agent -StartupType Automatic

Setup Multiple Keys​

If you have multiple SSH keys (for GitHub, different servers, etc...), you can create an SSH config file:

  1. Open the SSH config file:

    Linux/macOS:

    nano ~/.ssh/config

    Windows:

    notepad C:\Users\%USERNAME%\.ssh\config

  2. Add your configuration:

    Host myserver
        HostName remote_host
        User your_user
        IdentityFile ~/.ssh/id_rsa

    For example:

    Host myserver
        HostName 192.168.1.100
        User root
        IdentityFile C:\Users\hirusha\.ssh\id_rsa

Now, you can simply type:

ssh myserver

instead of the full ssh user@remote_host.

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