👤 Adding a New EC2 User with SSH Key Access and Passwordless Sudo

This guide explains how to securely create a new user on a Linux EC2 instance, configure SSH access using a .pem key file, and enable passwordless sudo access.

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🔧 Prerequisites

• Access to an existing EC2 instance
• A .pem private key file (e.g., <user_name>.pem)
• SSH access to the instance using an admin user (e.g., ec2-user)

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🪪 Step 1: Generate the Public Key from PEM

Generate a public key from your existing private key (.pem):

ssh-keygen -y -f <user_name>.pem

It will output a long line starting with ssh-rsa AAAA.... Copy this public key for later use.

👤 Step 2: Create a New User Without a Password

sudo adduser <user_name> --disabled-password

This creates a new user named <user_name> and disables password-based login.

🔒 Step 3: Add the User to the Sudo Group

sudo usermod -aG sudo <user_name>

This allows <user_name> to run commands as sudo.

📂 Step 4: Set Up SSH Directory and Key

Switch to the new user:

sudo su - <user_name>

Create the .ssh directory and set correct permissions:

mkdir ~/.ssh
chmod 700 ~/.ssh
touch ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys

Edit the authorized_keys file:

nano ~/.ssh/authorized_keys

Paste the public key ssh-rsa generate from Step 1 into this file and save it. Exit the <user_name> session:

exit

✅ Step 5: Configure Passwordless Sudo

Edit the sudoers file using a safe method:

sudo visudo

Add the following line:

<user_name> ALL=(ALL) NOPASSWD: ALL

Save and exit (Ctrl+X, then Y, then Enter).

🔁 Step 6: Test SSH and Sudo Access

From your local machine:

ssh -i <user_name>.pem <user_name>@<your-ec2-public-ip>

Then run a sudo command:

sudo whoami

Expected output:

root

Then try a sudo command:

sudo ls /root

Expected output:

You should not be prompted for a password anymore.

🛠 Optional (Security Consideration):

If you want to restrict <user_name> to specific commands (not full sudo), you can replace the line with something like:

<user_name> ALL=(ALL) NOPASSWD:/bin/systemctl restart apache2

📚 References:

• AWS EC2 User Management
• SSH Key Management
• Sudo Configuration