Module 2 Lesson 3: Core Docker CLI Commands

Docker is primarily a command-line tool. While the GUIs are nice, a professional engineer needs to be fast in the terminal. This lesson covers the "Essential 8" commands.

1. Image Commands (The Recipes)

docker pull <image>

Downloads an image from Docker Hub.

• Try it: docker pull nginx

docker image ls (or docker images)

Lists all images currently stored on your computer.

• Look for: Repository, Tag (version), and Size.

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2. Container Commands (The Instances)

docker run <image>

Creates AND starts a container. If the image isn't local, it pulls it first.

• Common Flags:
  • -d: Detached mode (runs in the background).
  • -it: Interactive terminal (allows you to type inside the container).
  • --name: Give your container a friendly name.
• Try it: docker run --name my-web -d nginx

docker ps

Lists all running containers.

• Tip: Use docker ps -a to see ALL containers, including stopped ones.

docker stop <container-id/name>

Gracefully shuts down a container.

• Try it: docker stop my-web

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3. Management & Cleanup

docker rm <container-id/name>

Deletes a stopped container.

• Tip: Use -f to force remove a running one (not recommended!).

docker rmi <image-id>

Deletes an image from your computer. (You can't delete an image if a container is currently using it).

docker exec -it <container-name> bash

"Jumps inside" an already running container.

• Try it: docker run -d --name helper alpine sleep 1000 -> docker exec -it helper sh.

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4. The Summary Table

Command	Action	When to use it?
pull	Download	You need a new tool/OS
run	Create + Start	You want to launch an app
ps	List	"Is my app running?"
stop	Shutdown	You want to save resources
rm	Delete	Cleanup old containers
images	List	"How much space is used?"
exec	Access	Debugging inside a container

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Exercise: The Command Sequence

Perform the following actions in your terminal:

1. Pull the image alpine (a tiny Linux distribution).
2. List your images to confirm it's there.
3. Run a container from alpine with the name my-test and have it run the command echo "hello docker".
4. Run docker ps. Why is the container not in the list? (Hint: what happens when a command finishes?)
5. Run docker ps -a. Is it there now? What is its "Status"?
6. Cleanup: Remove the my-test container and the alpine image.

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Summary

These 8 commands will cover 90% of your daily work with single containers. Mastering them makes the more advanced automation tools (like Compose) much easier to understand.

Next Lesson: We dive deeper into the storage layer: Understanding images and containers.