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
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
Displays the installed Docker version.
Show Docker Client & Daemon Version
docker version
Shows both the Docker Client and Docker Daemon versions.
Display Docker Information
docker info
Displays detailed information about your Docker installation.
2. Working with Images
Download an Image
docker pull hello-world:latest
Downloads the image from Docker Hub.
Note: If the image already exists locally, Docker won't download it again.
View Local Images
docker images
or
docker image ls
Lists all images stored locally.
Remove an Image
docker image rm <image_name_or_id>
or
docker rmi <image_name_or_id>
Deletes an image from your local machine.
3. Creating and Running Containers
Create a Container
docker create ubuntu
Creates a container but does not start it.
Start an Existing Container
docker start <container_id>
Starts a previously created container.
Create and Run a Container
docker run hello-world
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
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
Runs the container in the background.
4. Managing Containers
View Running Containers
docker ps
Lists only running containers.
View All Containers
docker ps -a
Lists both running and stopped containers.
Stop a Container
docker stop <container_id>
Stops a running container.
Restart a Container
docker restart <container_id>
Restarts a container.
Remove a Container
docker rm <container_id>
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
For example, if you're running Redis:
docker exec -it <container_id> redis-cli
6. Viewing Logs
Display Container Logs
docker logs <container_id>
Shows logs generated by the container.
Follow Logs in Real Time
docker logs -f <container_id>
Streams logs as they are generated.
7. Cleaning Up Docker Resources
Remove Unused Resources
docker system prune
This removes:
- Stopped containers
- Unused networks
- Dangling images
- Build cache
Remove All Unused Images
docker system prune -a
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!
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