Docker Setup on Ubuntu Server¶

This guide walks students through installing Docker Engine on an Ubuntu Server. It is adapted for course use from DigitalOcean's tutorial, How to Install Docker on Ubuntu, with additional classroom checkpoints and security notes.

Goal

By the end of this setup, your Ubuntu Server should be able to run Docker containers, pull images, and execute a basic test container.

1. Before You Start¶

You need:

An Ubuntu Server, preferably Ubuntu 22.04 LTS or 24.04 LTS.
A non-root user with sudo privileges.
Internet access from the server.
Terminal access through SSH, console, or a cloud provider terminal.

Check your Ubuntu version:

lsb_release -a

Expected result: the output should show Ubuntu and a release codename such as jammy for 22.04 or noble for 24.04.

Do not paste commands blindly

Read each command before running it. Docker installation changes system packages, adds an APT repository, and starts a privileged background service.

2. Update the Server¶

Start by refreshing the package list and applying available updates:

sudo apt update
sudo apt upgrade -y

Install required packages for repository access and certificate validation:

sudo apt install -y ca-certificates curl gnupg lsb-release

3. Remove Conflicting Docker Packages¶

If the server previously had Docker installed from Ubuntu's default repositories, remove conflicting packages first:

for pkg in docker.io docker-doc docker-compose docker-compose-v2 podman-docker containerd runc; do
  sudo apt remove -y "$pkg" 2>/dev/null || true
done

This does not delete Docker data under /var/lib/docker; it only removes conflicting packages.

4. Add Docker's Official GPG Key¶

Create the keyrings directory:

sudo install -m 0755 -d /etc/apt/keyrings

Download Docker's official GPG key:

curl -fsSL https://download.docker.com/linux/ubuntu/gpg   | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg

Set readable permissions:

sudo chmod a+r /etc/apt/keyrings/docker.gpg

5. Add Docker's APT Repository¶

Add Docker's stable repository for your Ubuntu version:

echo   "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu   $(. /etc/os-release && echo "$VERSION_CODENAME") stable"   | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Refresh package metadata again:

sudo apt update

Checkpoint: confirm Docker packages are coming from Docker's repository:

apt-cache policy docker-ce

Look for a candidate version from https://download.docker.com/linux/ubuntu.

6. Install Docker Engine¶

Install Docker Engine, the Docker CLI, containerd, Buildx, and Docker Compose plugin:

sudo apt install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

7. Verify Docker Service Status¶

Check whether Docker is running:

sudo systemctl status docker --no-pager

You should see:

Active: active (running)

If it is not running, start it:

sudo systemctl enable --now docker

8. Run a Test Container¶

Run Docker's official test image:

sudo docker run hello-world

Expected result: Docker downloads the hello-world image and prints a message confirming that the installation appears to be working.

9. Optional: Run Docker Without `sudo`¶

By default, Docker commands require root-level access. To allow your current user to run Docker commands without sudo, add the user to the docker group:

sudo usermod -aG docker $USER

Apply the group change by logging out and back in. For SSH users, disconnect and reconnect.

Then test:

docker run hello-world

Docker group security warning

Membership in the docker group is effectively root-equivalent on the host. Only add trusted users. On shared servers, ask the instructor before changing group membership.

10. Useful Docker Commands¶

Task	Command
Show running containers	`docker ps`
Show all containers	`docker ps -a`
List local images	`docker images`
Pull an image	`docker pull ubuntu:24.04`
Run an interactive Ubuntu container	`docker run -it ubuntu:24.04 bash`
Stop a container	`docker stop CONTAINER_ID`
Remove a stopped container	`docker rm CONTAINER_ID`
View container logs	`docker logs CONTAINER_ID`
Show Docker version	`docker version`
Show Docker system info	`docker info`
Check Docker Compose plugin	`docker compose version`

11. Classroom Checkpoint¶

Submit or record the following evidence for your lab notes:

Output of:
```
docker --version
```
Output of:
```
docker compose version
```
Screenshot or copied text showing successful output from:
```
docker run hello-world
```
One-sentence explanation of what a container is.

12. Troubleshooting¶

Problem: `Cannot connect to the Docker daemon`¶

Check whether Docker is running:

sudo systemctl status docker --no-pager

Start it if needed:

sudo systemctl enable --now docker

Problem: `permission denied while trying to connect to the Docker daemon socket`¶

Use sudo before Docker commands, or add your user to the docker group and log out/back in:

sudo usermod -aG docker $USER

Problem: Repository or GPG key error¶

Re-check these files:

ls -l /etc/apt/keyrings/docker.gpg
cat /etc/apt/sources.list.d/docker.list

Then run:

sudo apt update

Problem: Firewall behavior changes after Docker install¶

Docker modifies packet filtering rules for containers. On servers using ufw, exposed container ports may behave differently than expected. For production systems, review Docker's firewall documentation and use the DOCKER-USER chain for host-level filtering rules.

13. Clean Test Container Output¶

After testing, you can remove exited containers:

docker ps -a

Remove a specific stopped container:

docker rm CONTAINER_ID

Or remove all stopped containers:

docker container prune

Reference¶

DigitalOcean Community Tutorial: How to Install Docker on Ubuntu
Docker Docs: Install Docker Engine on Ubuntu

Next Step¶

Return to the Setup Course welcome page. For now, Docker setup is the only active setup module.