Your First Container

Table of Contents

1. Run Hello World
2. Pull an Image Explicitly
3. Run an Ubuntu Container & Interactive Mode
4. Detached Mode (-d)
5. Naming Containers (--name)
6. Removing Containers
7. Removing Images

Now that we understand Docker's architecture and core concepts, it's time to get hands-on with CLI commands. In this section, you'll run your first containers, learn execution modes, and manage system resources.

1. Run Hello World

The classic entry point to verify your Docker installation and understand the default pull-and-run behavior:

docker run hello-world

What happens under the hood?

• Docker checks if the hello-world image exists locally.

• If not found, it automatically pulls the image from Docker Hub.

• It creates a new container, executes the script inside, prints the output to your terminal, and then exits.

2. Pull an Image Explicitly

While docker run automatically pulls missing images, you can pre-fetch images using docker pull. This is useful when preparing deployment scripts or caching images ahead of time.

# Pull the official NGINX image without running it
docker pull nginx:alpine

# List locally downloaded images
docker images

3. Run an Ubuntu Container & Interactive Mode

By default, containers exit immediately if they don't have an active background process. To interact with an operating system container like Ubuntu, you must attach an interactive terminal session.

# Run Ubuntu with Interactive (-i) and TTY (-t) flags
docker run -it ubuntu bash

• -i (Interactive): Keeps STDIN open so you can pass input commands.

• -t (TTY): Allocates a pseudo-terminal, giving you a proper command prompt.

Once inside, you are running commands inside the isolated Ubuntu container:

# Example commands inside the container
root@a1b2c3d4e5f6:/# cat /etc/os-release
root@a1b2c3d4e5f6:/# exit

4. Detached Mode (-d)

For long-running services (like web servers or databases), you don't want the container attached to your current terminal session. Detached mode runs the container in the background.

# Run NGINX in detached mode
docker run -d nginx

# Check running containers
docker ps

To view what's happening inside a detached container:

# View container logs (use -f to stream/follow logs)
docker logs -f <CONTAINER_ID>

5. Naming Containers (--name)

By default, Docker assigns random generated names (e.g., focused_curie, eager_hopper). Assigning explicit names makes managing containers significantly easier in scripts and CLI commands.

# Run a named NGINX container
docker run -d --name my-web-server -p 8080:80 nginx

# Stop and check status using the custom name
docker stop my-web-server

6. Removing Containers

When a container stops, it is not deleted automatically; it remains on disk in a stopped state.

# List all containers (including stopped ones)
docker ps -a

# Remove a specific stopped container
docker rm my-web-server

# Force remove a currently running container (-f)
docker rm -f my-web-server

# Clean up all stopped containers at once
docker container prune

Tip: You can use the --rm flag with docker run to automatically remove a container as soon as it exits (great for temporary tasks or scripts):

docker run --rm ubuntu echo "Temporary task completed!"

7. Removing Images

To free up disk space on your host machine, you can clean up unused base images.

# List all local images
docker images

# Remove an image by ID or Tag (must remove dependent containers first)
docker rmi nginx:latest

# Remove all unused/dangling images
docker image prune -a

Summary Cheat Sheet