🐳 Docker Basics Every Beginner Should Know

When I started learning Docker, I quickly realized that understanding a few core concepts and commands makes working with containers much easier. Instead of memorizing commands, I wanted to understand what Docker does and why each command is useful.

In this article, I’m sharing my beginner notes. If you’re just getting started with Docker, this guide should help you build a solid foundation.

What is Docker?

Docker is a containerization platform that allows you to package an application together with all of its dependencies. This ensures the application runs consistently across different environments—whether it’s your local machine, a testing server, or production.

One of Docker’s biggest advantages is the famous phrase:

“It works on my machine.” → With Docker, it works on every machine.

Docker Architecture

Before learning the commands, it’s helpful to understand how Docker works behind the scenes.

Docker Client

The Docker Client is the command-line interface (CLI) that we use every day.

Whenever we run commands like:

docker run
docker ps
docker pull

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the Docker Client sends those requests to the Docker Daemon.

Docker Daemon

The Docker Daemon (dockerd) runs in the background.

It is responsible for:

• Building images
• Running containers
• Managing images
• Managing networks
• Managing volumes

Think of it as the engine that powers Docker.

Docker Image

A Docker Image is a read-only template that contains everything required to run an application:

• Application code
• Runtime
• Libraries
• Dependencies
• Configuration

Images are used to create containers.

Docker Container

A Container is a running instance of a Docker image.

Containers are:

• Lightweight
• Isolated
• Portable
• Fast to start

You can create multiple containers from the same image.

Docker Registry

A Docker Registry is where Docker images are stored and shared.

The most commonly used public registry is Docker Hub, where thousands of official and community images are available.

What is Containerization?

Containerization means packaging an application together with all of its dependencies so that it runs the same way everywhere.

Instead of worrying about different operating systems or missing libraries, Docker provides a consistent environment.

Essential Docker Commands

1. Check Docker Installation

Check Docker Version

docker -v

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Displays the installed Docker version.

Show Docker Client & Daemon Version

docker version

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Shows both the Docker Client and Docker Daemon versions.

Display Docker Information

docker info

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Displays detailed information about your Docker installation.

2. Working with Images

Download an Image

docker pull hello-world:latest

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Downloads the image from Docker Hub.

Note: If the image already exists locally, Docker won’t download it again.

View Local Images

docker images

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or

docker image ls

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Lists all images stored locally.

Remove an Image

docker image rm <image_name_or_id>

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or

docker rmi <image_name_or_id>

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Deletes an image from your local machine.

3. Creating and Running Containers

Create a Container

docker create ubuntu

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Creates a container but does not start it.

Start an Existing Container

docker start <container_id>

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Starts a previously created container.

Create and Run a Container

docker run hello-world

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If the image doesn’t exist locally, Docker downloads it first and then creates and starts the container.

Run an Interactive Ubuntu Container

docker run -it ubuntu

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Downloads the Ubuntu image (if needed), starts the container, and opens an interactive terminal where you can execute Linux commands.

Run a Container in Detached Mode

docker run -d nginx

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Runs the container in the background.

4. Managing Containers

View Running Containers

docker ps

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Lists only running containers.

View All Containers

docker ps -a

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Lists both running and stopped containers.

Stop a Container

docker stop <container_id>

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Stops a running container.

Restart a Container

docker restart <container_id>

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Restarts a container.

Remove a Container

docker rm <container_id>

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Deletes a stopped container.

5. Execute Commands Inside a Running Container

Open a Bash shell inside a running container:

docker exec -it <container_id> bash

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For example, if you’re running Redis:

docker exec -it <container_id> redis-cli

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6. Viewing Logs

Display Container Logs

docker logs <container_id>

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Shows logs generated by the container.

Follow Logs in Real Time

docker logs -f <container_id>

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Streams logs as they are generated.

7. Cleaning Up Docker Resources

Remove Unused Resources

docker system prune

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This removes:

• Stopped containers
• Unused networks
• Dangling images
• Build cache

Remove All Unused Images

docker system prune -a

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Removes all unused images, stopped containers, unused networks, and build cache.

Quick Summary

Command Purpose docker -v Check Docker version docker version Show Docker Client & Daemon version docker info Display Docker information docker pull Download an image docker images List local images docker run Create and run a container docker create Create a container docker start Start an existing container docker ps List running containers docker ps -a List all containers docker exec -it Execute commands inside a running container docker logs View container logs docker image rm Remove an image docker rm Remove a container docker system prune Clean up unused Docker resources

Final Thoughts

Docker is one of the most important tools in modern software development and DevOps. While there are many advanced topics to explore—such as Dockerfiles, Docker Compose, volumes, networking, Kubernetes, and container orchestration—mastering these fundamentals will make your learning journey much smoother.

I’m currently learning Docker as part of my DevOps roadmap, and I’ll continue sharing practical notes and examples as I progress.

If you have suggestions, best practices, or beginner tips, feel free to share them in the comments.

Happy Learning!