Docker Commands — The Kitchen Inventory

Back with our five friends — Riya, Arjun, Maya, Kabir, and Simran — who are building a college library app called Campus Library. They've been sending recipes (code) to each other, but the food always tastes different on different machines. Now they're using Docker — the magic lunch box — to pack the entire kitchen.

0 · Setup — Installing the Lunch Box

Before anyone can pack a lunch box, Docker needs to be on your computer.

Check Docker is installed

docker --version

Docker version 24.x.x, build xxxxxxx

Verify Docker is running

docker info

Remember

Docker needs the Docker Engine (the daemon) running in the background. If docker info fails, start Docker Desktop or the Docker service.

1 · docker pull — Stocking the Kitchen Shelf

Before you can cook, you need ingredients. A Docker image is a pre-packed kitchen — it contains the OS, libraries, runtime, and everything your app needs. Pulling an image downloads it to your computer.

Download an image from Docker Hub

docker pull ubuntu

Using default tag: latest
latest: Pulling from library/ubuntu
Digest: sha256:abc123...
Status: Downloaded newer image for ubuntu:latest
docker.io/library/ubuntu:latest

Remember

docker pull is like restocking your kitchen shelf. You do it once; the image stays until you remove it.

2 · docker images — What's on the Shelf?

See every image you have downloaded:

List all local images

docker images

REPOSITORY   TAG       IMAGE ID       CREATED        SIZE
ubuntu       latest    a]b1c2d3e4f5g   2 weeks ago    77.8MB
nginx        latest    1234567890ab   3 days ago     187MB

Remember

Images are the recipes. Containers are the actual lunches made from those recipes.

3 · docker run — Packing and Opening a Lunch Box

This is the most important command. docker run takes an image and starts a container — an actual running instance of that kitchen.

Run a container from an image

docker run ubuntu echo "Hello from the lunch box"

Hello from the lunch box

The container ran echo, printed the message, and stopped. That's a one-shot lunch box.

Run it interactively

Open a lunch box and step inside

docker run -it ubuntu bash

root@a1b2c3d4e5f6:/#

You're now inside the container's Ubuntu environment. Type exit to leave.

Common mistake

Forgetting -it means you can't interact with the container. You'll see it start and immediately stop, and wonder what happened.

Run it in the background

Pack the lunch box and let it run on its own

docker run -d --name my-web nginx

a1b2c3d4e5f6g7h8i9j0...

• -d = detached (runs in the background)
• --name = give the container a friendly name

Remember

docker run = docker create + docker start. It's the all-in-one "make me a lunch" command.

4 · docker ps — What's Cooking Right Now?

Check which containers are currently running:

List running containers

docker ps

CONTAINER ID   IMAGE   COMMAND                  CREATED          STATUS          PORTS     NAMES
a1b2c3d4e5f6   nginx   "/docker-entrypoint.…"   5 seconds ago    Up 5 seconds    80/tcp    my-web

List ALL containers (including stopped)

docker ps -a

Remember

docker ps without -a only shows running containers. Stopped ones are hidden. Use -a to see everything.

5 · docker stop / docker rm — Closing and Recycling the Lunch Box

Stop a running container

docker stop my-web

Remove a stopped container

docker rm my-web

Force-remove a running container

docker rm -f my-web

Common mistake

You can't remove a running container without -f. Always stop first, then rm, or use rm -f.

Clean up everything

Remove all stopped containers

docker container prune

Remove all unused images

docker image prune -a

6 · docker logs — What Did the Kitchen Say?

If a container is running in the background, you can't see its output. docker logs retrieves it:

See the output of a background container

docker logs my-web

/docker-entrypoint.sh: Configuration complete; ready for start up
172.17.0.1 - - [10/Oct/2024:12:00:00 +0000] "GET / HTTP/1.1" 200

Follow the logs in real time

docker logs -f my-web

Remember

docker logs is your debugging tool. If something's wrong, check the logs first.

7 · docker exec — Opening a Packed Lunch Box

Need to run a command inside an already-running container?

Open a shell inside a running container

docker exec -it my-web bash

root@a1b2c3d4e5f6:/#

Run a single command without entering

docker exec my-web cat /etc/nginx/nginx.conf

Remember

docker exec is like opening a lunch box that's already packed and taking a bite. You don't need to unpack the whole thing.

8 · docker build — Packing Your Own Lunch Box

The real power: create your own image from a recipe file called Dockerfile.

Dockerfile — The Recipe

FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
EXPOSE 3000
CMD ["node", "server.js"]

Build the image

docker build -t campus-library .

[+] Building 12.3s (8/8) FINISHED
 => [1/4] FROM node:20-alpine
 => [2/4] WORKDIR /app
 => [3/4] COPY package*.json ./
 => [4/4] RUN npm install
 => [5/4] COPY . .
 => => naming to docker.io/library/campus-library

• -t campus-library = tag (name) the image
• . = the build context (current folder)

Remember

docker build reads the Dockerfile step by step. Each instruction becomes a layer in the image — layers are cached and reused.

9 · docker-compose — Packing Multiple Lunch Boxes at Once

When your app has multiple services (web server + database + cache), docker-compose manages them all:

docker-compose.yml

services:
  web:
    build: .
    ports:
      - "3000:3000"
    depends_on:
      - db

  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: secret
    volumes:
      - db-data:/var/lib/postgresql/data

volumes:
  db-data:

Start everything at once

docker compose up -d

Stop everything

docker compose down

Remember

docker-compose is the lunch box carrier — it holds multiple lunch boxes together, each running its own service.

10 · docker volume — Storing Leftovers

Containers are ephemeral — when removed, their data is gone. Volumes persist data outside the container:

Create a volume

docker volume create library-data

List volumes

docker volume ls

Use a volume in a container

docker run -d \
  --name my-db \
  -v library-data:/var/lib/postgresql/data \
  postgres:16

Now even if you remove the container, the data in library-data survives.

Remember

Volumes are the Tupperware — they keep leftovers (data) safe even after the lunch box (container) is thrown away.

11 · docker network — Connecting Lunch Boxes

By default, containers can't talk to each other. Networks let them communicate:

Create a network

docker network create campus-net

Run containers on the same network

docker run -d --name my-web --network campus-net nginx
docker run -d --name my-db --network campus-net postgres:16

Now my-web can reach my-db by its name: my-db:5432.

Remember

Use bridge networks (the default) for single-host containers. Use overlay networks for multi-host (Docker Swarm).

Cheat Sheet

Command	Lunch box meaning
docker pull	Stock the kitchen shelf
docker images	What's on the shelf?
docker run	Pack and open a lunch box
docker ps	What's cooking right now?
docker stop	Close the lunch box
docker rm	Recycle the lunch box
docker logs	What did the kitchen say?
docker exec	Open a packed lunch box
docker build	Pack your own lunch box
docker compose up	Pack multiple lunch boxes at once
docker volume	Store leftovers
docker network	Connect lunch boxes