What is a Docker Container?

A Docker Container is a running instance of a Docker image. It is a lightweight, isolated, and portable unit that contains everything needed to run an application — code, runtime, libraries, and settings.

Think of an image as a class and a container as an object created from that class.

Container Lifecycle

Essential Container Commands

Example 1: Run a Simple Container

# Run nginx container in background (-d = detached mode)
docker run -d --name my-nginx -p 8080:80 nginx

Now open http://localhost:8080 in your browser — Nginx is running inside a container!

Example 2: Run Interactive Container

# Run ubuntu and open bash shell
docker run -it --name my-ubuntu ubuntu bash

Inside the container you can run Linux commands:

ls
pwd
apt-get update
exit

Example 3: List and Inspect Containers

# List running containers
docker ps

# List all containers
docker ps -a

# Inspect container details
docker inspect my-nginx

Example 4: Stop, Start, Remove Container

# Stop container
docker stop my-nginx

# Start stopped container again
docker start my-nginx

# Remove container (must be stopped first)
docker rm my-nginx

# Force remove running container
docker rm -f my-nginx

Example 5: Copy Files To/From Container

# Copy file from host to container
docker cp index.html my-nginx:/usr/share/nginx/html/

# Copy file from container to host
docker cp my-nginx:/usr/share/nginx/html/index.html ./

Run Flags Reference

Summary

• A container is a running instance of a Docker image.
• Use docker run to start containers and docker ps to list them.
• Use -d for background mode and -p to map ports.
• Use docker exec -it to enter a running container shell.