docker

Additional Notes

docker manages lightweight, portable containers that package applications with their dependencies. It provides commands for building images, running containers, managing storage, configuring networking, and orchestrating multi-container workflows. Docker uses a client-server architecture where the docker CLI communicates with the dockerd daemon.

Containers are created from images stored in registries such as Docker Hub. Images are built using Dockerfile instructions in a layered format, allowing efficient reuse and distribution. Docker is widely used for development environments, CI/CD pipelines, microservices, and production deployment.

Syntax

docker [command] [options] [arguments]

Parameters

• command: A subcommand such as run, build, pull, ps, stop, rm, exec, or logs.

Common Global Options

• -D, --debug: Enable debug mode.
• -H, --host: Daemon socket to connect to (e.g., unix:///var/run/docker.sock or tcp://...).
• -v, --version: Print version information.

Common Commands

• docker run [options] IMAGE [command]: Create and start a container from an image.
• docker ps [options]: List running containers. Use -a to show all containers.
• docker images: List available images.
• docker pull IMAGE: Download an image from a registry.
• docker build -t NAME .: Build an image from a Dockerfile in the current directory.
• docker stop CONTAINER: Gracefully stop a running container.
• docker rm CONTAINER: Remove a stopped container.
• docker rmi IMAGE: Remove an image.
• docker exec -it CONTAINER command: Run a command in a running container.
• docker logs CONTAINER: Fetch the logs of a container.
• docker compose up: Start services defined in compose.yaml.

Container Run Options

• -d, --detach: Run the container in the background.
• -it: Run interactively with a terminal (combine -i and -t).
• -p HOST:CONTAINER: Publish a container port to the host.
• -v HOST:CONTAINER: Mount a volume or host directory.
• --name NAME: Assign a name to the container.
• --restart POLICY: Set the restart policy (no, always, on-failure, unless-stopped).
• -e KEY=VALUE: Set environment variables.
• --rm: Automatically remove the container when it exits.
• --network NETWORK: Connect the container to a network.

Examples

docker run -it ubuntu bash

Start an interactive Ubuntu container with a bash shell.

docker run -d -p 80:80 --name web nginx

Start Nginx as a background container, mapping host port 80 to container port 80.

docker build -t myapp .

Build an image named myapp from a Dockerfile in the current directory.

docker ps -a

List all containers, including stopped ones.

docker exec -it myapp sh

Open a shell inside a running container named myapp.

docker logs -f myapp

Follow the log output of a container in real time.

docker compose up -d

Start all services defined in compose.yaml in the background.

Practical Notes

• Running docker requires the daemon (dockerd) to be running. Use systemctl start docker or enable it with systemctl enable docker.
• To run docker without sudo, add your user to the docker group, then log out and back in.
• Images are versioned by tags. docker pull ubuntu:22.04 pulls a specific release.
• Use docker system prune to clean up unused containers, images, and networks.
• Data in a container is lost when the container is removed unless stored in a volume.
• For orchestration across multiple hosts, use Docker Swarm or Kubernetes.
• Docker Compose files (compose.yaml or docker-compose.yml) define multi-container applications.