Docker for Beginners: A Complete Guide to Installation and Essential Commands

Introduction

Docker has become one of the most widely used tools in modern DevOps workflows, and for good reason. It lets developers package an application together with everything it needs code, runtime, libraries, and system tools into a single lightweight unit called a container. That container runs the same way on your laptop, a test server, or in production, which eliminates the classic “it works on my machine” problem.

If you’re just getting started with Docker, this guide walks you through installing it on Ubuntu and covers the essential commands you’ll use every day, from pulling your first image to managing containers, volumes, and network ports.

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What Is Docker?

Docker is a platform for building, shipping, and running applications inside isolated environments called containers. Unlike a full virtual machine, a container shares the host system’s kernel, which makes it much faster to start and far more efficient with system resources.

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Installing Docker on Ubuntu

Setting up Docker on an Ubuntu machine involves a few straightforward steps. The commands below work the same way across most Linux distributions, though installation steps can vary slightly depending on your base OS.

Step 1: Install Required Dependencies

sudo apt-get install -y --no-install-recommends \
apt-transport-https \
ca-certificates \
curl \
software-properties-common

Step 2: Add the Docker GPG Key

curl -fsSL https://apt.dockerproject.org/gpg | sudo apt-key add -

Step 3: Add the Docker Repository

add-apt-repository \
"deb https://apt.dockerproject.org/repo/ \
ubuntu-$(lsb_release -cs) \
main"

Step 4: Update Package Lists

apt-get update

Step 5: Install the Docker Engine

apt-get -y install docker-engine

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Docker’s Basic Directory Structure

Once installed, Docker stores its data in a predictable set of directories:

Path	Purpose
/var/lib/docker	Base directory for all Docker data
/var/lib/docker/container	Stores container information
/var/lib/docker/container/<container-longname>/hostconfig.json	Full host configuration details for a container
/var/lib/docker/volumes/<volumeID>/_data	Persistent data created inside a container’s volume

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Essential Docker Commands

Running Your First Container

Test your installation by pulling and running the classic hello-world image:

docker run hello-world

To pull an Ubuntu image and drop into an interactive terminal:

docker run -it ubuntu bash

Working with Images

View all images available locally:

docker images

Tag an image before pushing it to a registry:

docker tag 73fd91f23a84 pheonixsolutions/docker-whale:latest

(73fd91f23a84 is the image ID.)

Pushing and Pulling Images from Docker Hub

Create a free account at hub.docker.com, then log in from the terminal:

docker login

Push a tagged image to your Docker Hub repository:

docker push pheonixsolutions/docker-whale

Pull and run an image from a repository:

docker run pheonixsolutions/docker-whale

Managing Containers

Start an interactive container session:

docker run -ti ubuntu:14.04 /bin/bash

Press Ctrl + P + Q to detach from the container without stopping it.

List currently running containers:

docker ps

Reattach to a running container using its ID:

docker attach c26fe223abeb

List all containers, including stopped ones:

docker ps -a

Start a stopped container:

docker start 196b121e371b

Stop a running container:

docker stop 196b121e371b

Run a named, detached container:

docker run -d -ti --name=pheonixcontainer ubuntu:14.04 /bin/bash

Here, -d detaches the container so it runs in the background, and --name assigns it a readable name.

Working with Volumes

Mount a volume inside the container at /data:

docker run -ti -v /data --name=pheonixvolume ubuntu:14.04

Mount a specific host directory into the container:

docker run -ti -v /home/pheonixsolutions:/data --name=pheonixvolume ubuntu:14.04

The -v flag defines the container’s mount point.

Mapping Ports

Expose a container port (e.g., for MySQL):

docker run -d -p 3306 -ti --name=mysql1 mysql /bin/bash

Forward a specific host port to the container:

docker run -d -p 80:80 -ti --name=mysql2 mysql /bin/bash

The 80:80 mapping forwards requests on host port 80 to the container’s port 80.

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Conclusion

Docker simplifies how applications are built, packaged, and deployed by wrapping everything an app needs into a portable container. Once you’re comfortable with the basics installing Docker, pulling and tagging images, managing containers, and mapping volumes and ports you have the foundation needed to explore more advanced DevOps workflows like Docker Compose and container orchestration with Kubernetes.

Start small: run the hello-world image, spin up an Ubuntu container, and get hands-on with the commands above. The best way to learn Docker is by using it.

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