How to setup passwordless SSH authentication

To set up passwordless SSH login from your Windows machine (rd211) to your Ubuntu server (rahul), follow these steps:

Step 1: Generate an SSH Key on Windows

On your Windows laptop, open PowerShell or Command Prompt and run:

ssh-keygen -t rsa -b 4096

• When prompted for a file location, press Enter to save it in the default location:
  C:\Users\rd211\.ssh\id_rsa
• If prompted for a passphrase, you can leave it empty.

Step 2: Copy the Public Key to the Ubuntu Server

Now, transfer your public key to the Ubuntu server.

Method 1: Using ssh-copy-id (Recommended)

If your Ubuntu server allows SSH password login, run from PowerShell:

ssh-copy-id rahul@<server-ip>

It will ask for Rahul’s password once, then set up key-based login.

Method 2: Manually Copying the Key

If ssh-copy-id is not available, do the following:

1. Open PowerShell and display the public key:

   Get-Content $HOME\.ssh\id_rsa.pub
   

2. Copy the output.

3. Log in to your Ubuntu server manually:

   ssh rahul@<server-ip>
   

4. On the Ubuntu server, create the .ssh directory and authorized keys file:

   mkdir -p ~/.ssh && chmod 700 ~/.ssh
   echo "<PASTE_YOUR_PUBLIC_KEY_HERE>" >> ~/.ssh/authorized_keys
   chmod 600 ~/.ssh/authorized_keys
   

5. Exit from the Ubuntu server:

   exit
   

Step 3: Verify SSH Key Login

Now, try logging in without a password:

ssh rahul@<server-ip>

If everything is set up correctly, you should be logged in without being prompted for a password.

Step 4: Disable Password Authentication (Optional, for Security)

To force SSH key-based authentication only, do the following on the Ubuntu server:

1. Open the SSH configuration file:

   sudo nano /etc/ssh/sshd_config
   

2. Find and update these lines:

   PasswordAuthentication no
   PubkeyAuthentication yes
   

3. Restart SSH service:

   sudo systemctl restart ssh
   

Now, only SSH keys will work for authentication.