Installing and using Docker

Docker bundles a program together with its whole runtime environment so it runs the same way on any server. This guide is based on an Ubuntu server.

1. Install

Use Docker's official install script.

curl -fsSL https://get.docker.com | sudo sh

To avoid adding sudo every time, add your account to the docker group and reconnect.

sudo usermod -aG docker $USER

Check that it installed correctly.

docker run --rm hello-world

If you see "Hello from Docker!", it worked.

2. Try running a container

Let's start a web server (Nginx).

docker run -d --name web -p 80:80 --restart unless-stopped nginx

-d Run in the background
-p 80:80 Connect the server's port 80 to the container's port 80
--restart unless-stopped Start again automatically even after the server reboots

Go to http://server-ip in your browser and you'll see the Nginx page.

3. Common commands

docker ps                 # List running containers
docker logs -f web        # View logs (Ctrl + C to exit)
docker restart web        # Restart
docker stop web           # Stop
docker rm web             # Remove (after stopping)
docker images             # List downloaded images
docker system df          # Disk space used by Docker

4. Several at once with Docker Compose

You can manage several containers together with a single configuration file. Create a compose.yaml file.

services:
  web:
    image: nginx
    ports:
      - "80:80"
    restart: unless-stopped

docker compose up -d      # Start
docker compose down       # Stop and remove
docker compose logs -f    # View logs

⚠️ Firewall warning

Ports opened with Docker (-p) are opened to the outside, ignoring your ufw firewall settings. For containers that should only be used inside the server, like a DB, bind them only to 127.0.0.1 as shown below.

docker run -d --name db -p 127.0.0.1:3306:3306 -e MARIADB_ROOT_PASSWORD=long-password mariadb

For firewall settings, see Opening firewall ports.

My disk is full

Unused images and containers take up a lot of disk space as they pile up.

docker system prune

This cleans up containers that aren't running and images you don't use. Check that it's okay to delete them, then type y.