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- 01Getting Started
- 02What Is Docker?
- 03Checking the Version with docker --version
- 04Images vs. Containers
- 05Fetching an Image with docker pull
- 06Listing Images with docker images
- 07Starting a Container with docker run
- 08Running in the Background with docker run -d
- 09Listing Running Containers with docker ps
- 10Listing Every Container with docker ps -a
- 11Naming a Container with docker run --name
- 12Stopping a Container with docker stop
- 13Restarting a Stopped Container with docker start
- 14Restarting with docker restart
- 15Deleting a Container with docker rm
- 16Deleting an Image with docker rmi
- 17Publishing a Port with docker run -p
- 18Passing Environment Variables with docker run -e
- 19Mounting a Volume with docker run -v
- 20Running Commands Inside a Container with docker exec
- 21Reading Logs with docker logs
- 22Inspecting Details with docker inspect
- 23Viewing Processes with docker top
- 24Monitoring Resources with docker stats
- 25Copying Files with docker cp
- 26What Is a Dockerfile?
- 27Choosing a Base Image with FROM
- 28Setting the Working Directory with WORKDIR
- 29Adding Files with COPY
- 30Executing Commands with RUN
- 31Setting the Startup Command with CMD
- 32Declaring Ports with EXPOSE
- 33Building an Image with docker build
- 34Tagging an Image with docker tag
- 35Sharing an Image with docker push
- 36What Is .dockerignore?
- 37What Is a Multi-Stage Build?
- 38Creating a Volume with docker volume create
- 39Listing Volumes with docker volume ls
- 40Creating a Network with docker network create
- 41Listing Networks with docker network ls
- 42What Is Docker Compose?
- 43Starting Everything with docker compose up
- 44Stopping Everything with docker compose down
- 45Cleaning Up with docker system prune
Setting the Startup Command with CMD
When you want to define what the container does when it starts, use CMD. It sets the default command executed at container start.
The syntax is CMD ["executable", "arg"]. Only the last CMD in a Dockerfile takes effect.
Writing CMD ["node", "app.js"] means the container runs your Node application on start, unless the caller overrides it.
A common stumble is writing several CMD instructions and wondering why only one runs. To run multiple things, use a startup script.
In real work, CMD defines the one main process of the container — and when that process exits, the container stops.
🧑💻 You can type this command into the Docker pseudo terminal to try it yourself (this page itself has no interactive terminal).