Docker Commands

This section covers essential Docker commands for managing images, containers, and volumes.

Important Note: Unless you’ve configured Docker to run as a non-root user (highly recommended - see the “Getting Started” section), you’ll need to use sudo before each docker command.

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General Commands

• docker --help

  • Description: Displays a list of all available Docker commands and their descriptions. Use this to get help on any Docker command.

  • Example Usage:

    docker --help
    docker <command> --help  # Get help on a specific command (e.g., docker run --help)
    

• docker info

  • Description: Displays system-wide information about the Docker installation, including the number of containers and images, kernel version, and storage driver.

  • Example Usage:

    docker info
    

• docker version

  • Description: Displays the Docker version information for both the client and server.
  • Example Usage:

    docker version
    

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Image Management

• docker pull

  • Description: Downloads a Docker image from a registry (e.g., Docker Hub).

  • Example Usage:

    docker pull ubuntu:22.04     # Pull the Ubuntu 22.04 image
    docker pull nginx:latest      # Pull the latest version of the Nginx image
    docker pull myregistry/myimage:mytag  # Pull an image from a private registry
    

• docker images

  • Description: Lists the Docker images available on your local system.

  • Example Usage:

    docker images
    docker images -a             # Show all images (including intermediate layers)
    docker images --digests     # show image digests
    docker images --filter "dangling=true"   # show danling images
    

• docker rmi

  • Description: Removes (deletes) one or more Docker images. You cannot remove an image that is being used by a container.

  • Example Usage:

    docker rmi ubuntu:22.04       # Remove the Ubuntu 22.04 image (by tag)
    docker rmi <image_id>        # Remove an image by its ID
    docker rmi $(docker images -q) # Remove ALL images (BE CAREFUL!) - uses command substitution
    docker image prune          # remove dangling images
    docker image prune -a       # Remove all unused images
    

• docker build

  • Description: Builds a Docker image from a Dockerfile.
  • Example Usage:

     docker build -t my-image:latest .  # build an image and give it a name.
    

    Explanation:

    • -t tag the image with a human-readable name.
    • . build the image from the current directory.

• docker tag

  • Description: creates a tag TARGET_IMAGE that refers to SOURCE_IMAGE
  • Example Usage:

    docker tag my-image:latest my-repo/my-image:v1.0 # tag an image.
  

• docker push

  • Description: pushes the image to a registry.
  • Example Usage:

      docker push my-repo/my-image:v1.0
    

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Container Management

• docker run

  • Description: Creates and starts a new container from a Docker image. This is one of the most important Docker commands.

  • Example Usage:

    docker run -it --name my_container ubuntu:22.04  # Run an interactive Ubuntu container
    docker run -d --name my_nginx -p 8080:80 nginx:latest  # Run an Nginx container in detached mode, mapping port 8080 on the host to port 80 in the container
    docker run -it --rm ubuntu:22.04 bash            # Run a container and automatically remove it when it exits
    docker run -v $(pwd):/app -w /app my_image python my_script.py  # Run a container with a volume mount and working directory
    docker run --env MY_VAR=my_value my_image      # Set an environment variable inside the container
    

  Key Options:

  • -i (--interactive): Keep STDIN open even if not attached (allows you to interact with the container).
  • -t (--tty): Allocate a pseudo-TTY (connects your terminal to the container’s terminal). Use -it together for interactive sessions.
  • -d (--detach): Run the container in detached mode (in the background).
  • --name: Assign a name to the container.
  • -p HOST_PORT:CONTAINER_PORT: Publish a container’s port to the host.
  • --rm: Automatically remove the container when it exits.
  • -v HOST_PATH:CONTAINER_PATH: Mount a volume (bind mount). This allows you to share files between the host and the container.
  • -w WORKDIR: Set the working directory inside the container.
  • --env VAR=VALUE: Set environment variables inside the container.

• docker ps

  • Description: Lists running containers.

  • Example Usage:

    docker ps         # List running containers
    docker ps -a      # List all containers (running and stopped)
    docker ps -q      # List only container IDs
    

• docker stop

  • Description: Gracefully stops a running container.

  • Example Usage:

    docker stop my_container  # Stop the container named 'my_container'
    docker stop $(docker ps -q)  # Stop all running containers
    

• docker start

  • Description: Starts a stopped container.
  • Example Usage:

    docker start my_container
    

• docker rm

  • Description: Removes (deletes) one or more stopped containers.

  • Example Usage:

    docker rm my_container      # Remove the container named 'my_container'
    docker rm $(docker ps -a -q) # Remove ALL containers (BE CAREFUL!)
    docker container prune      # remove all stopped containers
    

• docker exec

  • Description: Runs a command inside a running container. Very useful for debugging and interacting with a running container.

  • Example Usage:

    docker exec -it my_container bash  # Open an interactive shell inside 'my_container'
    docker exec my_container ls -l /app # List the contents of the /app directory inside the container
    

• docker logs

  • Description: displays the logs of a container.
  • Example Usage:

      docker logs my_container # displays the logs
      docker logs -f my_container # real time logs
    

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Volume Management

• docker volume ls

  • Description: list all volumes.

  • Example Usage:

       docker volume ls
    

• docker volume create
  • Description: create a volume.
  • Example Usage:

       docker volume create my_volume
    

• docker volume rm
  • Description: Remove a volume.
  • Example Usage:

       docker volume rm my_volume
    

• docker volume prune
  • Description: Remove all unused volumes.
  • Example Usage:

       docker volume prune
    

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Copying Files

• Copy a file from container to local host

  docker cp my_container:usr/src/project/file .
  

• Copy a file from local host to container

  docker cp file my_container:/usr/src/project
  

• docker cp

  • Description: Copies files/directories between a container and the local filesystem.

  • Example Usage:

    docker cp my_container:/path/in/container /local/path  # Copy *from* container *to* host
    docker cp /local/path my_container:/path/in/container  # Copy *from* host *to* container
    

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