🐧 Linux Commands Every DevOps Beginner Learns While Deploying to EC2

🔐 1. SSH & Remote Access

ssh -i DevOps.pem [e-mail]

Purpose: Connect securely to an EC2 instance.

• ssh → Secure Shell
• i DevOps.pem → Use this private key for authentication
• ec2-user@host → Login user + EC2 hostname

👉 This is how you manually access EC2.

---

ssh user@host "command"

Purpose: Run a command on EC2 without logging in interactively.

Used in GitHub Actions to:

• Verify connection

• Create directories

• Reload Nginx

Example:

ssh ec2-user@EC2_HOST "whoami && hostname"

ssh-keyscan -H EC2_HOST >> ~/.ssh/known_hosts

Purpose: Trust EC2’s SSH fingerprint automatically.

• Prevents the “Are you sure you want to continue connecting?” prompt

• Required for non-interactive CI/CD

We later made it safer:

ssh-keyscan -T 10 -H EC2_HOST >> ~/.ssh/known_hosts || true

📁 2. File System Navigation & Inspection

pwd -- Print current directory path.

ls -- List files and directories

Variants:

• ls -l → permissions, owner, size

• ls -a → include hidden files

cd directory - Change directory

Example:

cd DevOpsWeb

🔑 3. File & Directory Permissions (VERY IMPORTANT)

chmod - Change permissions

Examples:

chmod 755 directory
chmod 644 file

Meaning:

• 7 = read + write + execute (owner)
• 5 = read + execute (group/others)
• 4 = read only

Used to:

• Let Nginx read files

• Prevent 403 Forbidden errors

chown - Change ownership

sudo chown -R ec2-user:nginx /home/ec2-user/DevOpsWeb

• Owner → ec2-user

• Group → nginx

• -R → recursive

👉 This allowed Nginx to read your deployed files.

sudo - Run command as root (admin)

Used for:

• Installing packages

• Editing system configs

• Restarting services

🌐 4. Nginx (Web Server)

sudo yum install nginx -y - Install Nginx on Amazon Linux.

sudo systemctl start nginx - Start the Nginx service.

sudo systemctl enable nginx - Start Nginx automatically on reboot.

sudo systemctl status nginx - Check if Nginx is running and healthy.

sudo nginx -t - Test Nginx configuration for syntax errors.

👉 Always do this before reloading.

sudo systemctl reload nginx - Reload config without downtime.

🌍 5. Networking & Debugging

curl http://localhost

Test if the web server is responding **locally **on EC2.

If this works but browser doesn’t:

• Security Group issue

• Firewall issue

curl http://PUBLIC_IP - Test public access from EC2 itself.

lsof -i :80 - Check what is using port 80.

Used to confirm:

• Nginx is listening

• Apache was conflicting earlier

📦 6. Package Management

sudo yum install package -y - Install software non-interactively.

Examples:

sudo yum install httpd -y
sudo yum install docker -y

sudo yum remove httpd -y - Remove Apache to avoid port conflicts with Nginx.

🐳 7. Docker Basics (So Far)

docker run hello-world - Verify Docker installation.

docker build -t devops-website - Build Docker image from Dockerfile.

docker ps -a - List all containers (running + stopped).

docker exec -it container command - Run a command inside a running container.

Example:

docker exec -it devopsweb ls /usr/share/nginx/html

sudo usermod -aG docker ec2-user - Allow ec2-user to run Docker without sudo.

Requires logout/login to take effect.

8. Rsync (CI/CD Deployment)

rsync -avz --delete

Efficient file sync over SSH.

• -a → archive mode (permissions, timestamps)

• -v → verbose

• -z → compression

• --delete → remove files not present in source

Used to deploy:

WSL → GitHub → GitHub Actions → EC2

--exclude
Prevent syncing unwanted files:

--exclude='.git*'
--exclude='.github/'

--chmod
Force permissions on destination:

--chmod=Du=rwx,Dgo=rx,Fu=rw,Fgo=r

This solved exit code 23 and permission issues.

🧪 9. GitHub Actions / CI Commands

set -e - Exit immediately if a command fails.

set -eux

• -e → exit on error

• -u → fail on undefined variables

• -x → print commands (debugging)

Used to make pipelines fail loudly and clearly.

mkdir -p ~/.ssh - Create directory safely (no error if exists).

echo "$SECRET" > ~/.ssh/id_rsa - Write SSH key from GitHub Secrets.