Core Concepts

docker --version
docker run hello-world
docker --help
docker <command> --help

Working with Images

docker image ls                    # list local images
docker pull ubuntu                 # pull latest Ubuntu image
docker pull ubuntu:22.04           # pull a specific tag
docker image rm ubuntu             # remove a local image
docker image prune                 # remove unused dangling images
docker build -t myapp:1.0 .        # build image from Dockerfile in current dir
docker tag myapp:1.0 myapp:latest  # tag an image
docker push myrepo/myapp:1.0       # push to a registry

Running Containers

# Interactive terminal
docker run -it ubuntu bash

# Detached web server with port mapping and name
docker run -d -p 80:80 --name webserver nginx

# Auto-remove on exit, port mapped, CPU-limited
docker run -d -p 3000:3000 --cpus 2 --name react --rm alpine-npm /bin/ash

# Bind-mount current directory into container
docker run -it -v $(pwd):/workspace ubuntu bash

Managing Containers

docker container ls               # list running containers
docker container ls --all         # list all (including stopped)
docker container stop webserver   # stop gracefully
docker container start webserver  # start a stopped container
docker container restart webserver
docker container rm webserver     # remove a stopped container
docker container rm -f webserver  # force-remove a running container

docker attach webserver           # attach to container stdout
docker exec -it webserver bash    # open a new shell in running container
# Ctrl-P then Ctrl-Q to detach without stopping

docker logs webserver             # show container logs
docker logs -f webserver          # follow logs in real time
docker inspect webserver          # full JSON metadata

Volumes

Volumes persist data beyond the container lifecycle. Prefer named volumes over bind mounts for database data.

docker volume create mydata
docker volume ls
docker volume inspect mydata
docker volume rm mydata

# Mount a named volume
docker run -d -v mydata:/var/lib/mysql mysql

# Bind mount current directory
docker run -it -v $(pwd):/app -w /app python:3.12 bash

Dockerfile Basics

A Dockerfile defines how to build an image. A minimal Python app example:

FROM python:3.12-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
EXPOSE 5000
CMD ["python", "app.py"]

Docker Compose

Compose runs multi-container applications defined in a docker-compose.yml:

services:
  web:
    build: .
    ports: ["5000:5000"]
    depends_on: [db]
  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: secret
    volumes: [pgdata:/var/lib/postgresql/data]
volumes:
  pgdata:

docker compose up -d      # start all services in background
docker compose down       # stop and remove containers
docker compose logs -f    # follow logs for all services
docker compose ps         # list service status
docker compose build      # rebuild images

Cleanup

docker container prune    # remove all stopped containers
docker image prune        # remove dangling images
docker image prune -a     # remove ALL unused images
docker volume prune       # remove unused volumes
docker system prune       # containers + networks + dangling images
docker system prune -a    # full clean (use with caution)
docker system df          # show disk usage by Docker objects

Run docker system df first to see how much space Docker is consuming before pruning.