Docker containers operate as isolated micro-linux environments, each possessing its own network stack and IP address. The relationship between images and containers is foundational: an image is a static, read-only template (the filesystem), whereas a container is a running instance (the process) derived from that template. A single image can spawn multiple concurrent containers.

System-Level Utilities

docker version       # Verify CLI and daemon versions
docker system info   # Display system-wide information
docker --help        # List available commands and flags

Image Operations

docker images                     # List locally available images
docker pull nginx:1.25           # Download a specific image from a registry
docker search python             # Query the Docker Hub for images
docker image inspect <image_id>  # Retrieve low-level image metadata

docker rmi <image_id>            # Delete a specific image
docker rmi -f $(docker images -q) # Forcefully remove all local images

Container Lifecycle Maangement

# Running a container
docker run [options] <image_id_or_name>
# Options:
#   -d                  : Run in detached mode (background)
#   -it                 : Run interactively with a terminal
#   -p <host>:<container>: Map host port to container port

# Example: Interactive Ubuntu shell
docker run -it ubuntu:latest /bin/bash

# Example: Background web server with port mapping
docker run -d -p 8080:80 nginx:latest

# Monitoring containers
docker ps            # List active containers
docker ps -a         # List all containers (active and stopped)
docker ps -n 3       # Show the 3 most recently created containers
docker ps -q         # Output only container IDs

# Interacting with running containers
docker exec -it <cid> /bin/bash  # Open a new terminal inside the container
docker attach <cid>              # Attach to the primary process of the container

# Exiting an interactive session:
#   exit          : Terminate the container and exit
#   Ctrl+P, Ctrl+Q : Detach from the container, leaving it running in the background

# State transitions
docker start <cid>    # Start a stopped container
docker restart <cid>  # Restart a running container
docker stop <cid>     # Gracefully stop a container
docker kill <cid>     # Forcefully terminate a container

# Removing containers
docker rm <cid>                      # Remove a stopped container
docker rm -f <cid>                   # Force remove a running container
docker rm -f $(docker ps -aq)        # Force remove all containers
docker ps -aq | xargs docker rm      # Alternative method to remove all stopped containers

# Diagnostics and File Operations
docker logs <cid>                           # Fetch container stdout/stderr logs
docker top <cid>                            # List running processes inside the container
docker inspect <cid>                        # Inspect container configuration and state
docker cp <cid>:/var/log/app.log ./app.log  # Copy files from container to host

Persisting Container State

Modifications made inside a running container can be saved as a new image using the commit operation.

docker commit -m "Added custom modules" <container_id> custom_image_name:v1.0