⚙️ Docker CLI Mastery: Understanding Containers From the Terminal

📅 Day 2 of My Docker Sprint

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🚀 Quick Recap of Day 1

Yesterday I explored the history and motivation behind Docker, learned about the evolution from bare metal → VMs → containers, and ran my first docker run hello-world command.

Today, it’s time to get our hands dirty with the Docker CLI — the terminal interface that gives us full power over containers, images, volumes, and more.

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🧠 Why Learn the CLI First?

While Docker Desktop and GUI tools are available, real DevOps engineers live in the terminal. The CLI:

• Offers full control

• Works in CI/CD pipelines

• Trains you for production environments

• Makes automation possible

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🔧 Key Docker CLI Commands I Practiced Today

1. docker --version

Check if Docker is installed and running:

docker --version

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2. docker pull

Download an image from Docker Hub:

docker pull alpine

Alpine is a tiny Linux image (just ~5MB) great for testing.

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3. docker images

List all downloaded images:

docker images

🔎 Output includes image name, tag, size, and ID.

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4. docker run

Run a container from an image:

docker run alpine echo "Hello from container!"

📌 This runs Alpine and prints a message, then exits.

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5. docker ps

List running containers:

docker ps

Add -a to list all containers, even stopped ones:

docker ps -a

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6. docker stop & docker rm

Stop and remove containers:

docker stop <container_id>
docker rm <container_id>

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7. docker rmi

Remove an image:

docker rmi alpine

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8. docker exec

Run commands inside a running container:

docker exec -it <container_id> sh

Opens a shell inside the container 🔥

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💥 Key Concepts I Learned Today

• Image: A blueprint for the container (like a snapshot)

• Container: A running instance of an image

• -it flag: Interactive + pseudo-TTY (lets you type into the container)

• Ephemeral nature: Containers are stateless by default unless volumes are used

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💡 Mistakes I Made

• Forgot -it, so my shell exited immediately 😅

• Confused image ID with container ID

• Tried to stop a container that had already exited

But that’s the beauty of learning in public — you document the bugs, too!

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🔁 What’s Next (Day 3 Preview)

Tomorrow I’ll explore:

• Building my own Dockerfile

• Understanding layers and caching

• Creating a custom image from scratch

• Running a web server (Nginx or Node.js)

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🧠 Final Thoughts

Day 2 gave me confidence with the CLI. Docker is no longer a black box — I’m finally understanding how it pulls, builds, and runs everything.

This is the real DevOps playground, and I’m just getting started.
See you on Day 3. Let’s containerize everything 🚀

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🔖 Tags

#Docker #DevOps #LearnInPublic #BuildInPublic #Hashnode #CloudEngineering #Containers

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