Installing Docker & Your First Command

In one line

Get Docker running on your machine and prove it works with the smallest possible container — this is the 'Hello World' every Docker journey starts with, and it's worth understanding every word of the output.

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Key ideas

01
Docker Desktop (Windows/Mac) bundles the daemon, CLI, and a GUI into one installer — the easiest path for most developers. On Linux, you typically install the Docker Engine directly (no GUI needed, since Linux already has a native kernel with the required features).
02
After installing, docker --version confirms the CLI is installed, and docker info confirms the DAEMON is actually running and reachable — a common early mistake is having the CLI installed but the daemon not started (Docker Desktop not launched), which produces a 'Cannot connect to the Docker daemon' error.
03
The classic first command: docker run hello-world. This single command exercises your ENTIRE architecture from Topic 0.3: the client sends the request, the daemon checks locally (not found), pulls the tiny hello-world image from Docker Hub, creates a container from it, runs it (it just prints a message and exits), and the container's output appears in your terminal.
04
Reading the hello-world output line by line teaches you the whole pull-and-run flow: it literally describes each step ('Docker Client contacted the Docker Daemon', 'the Daemon pulled the image from Docker Hub', 'the Daemon created a new container') — read it once, slowly, the first time you run it.
05
docker ps shows RUNNING containers (empty right after hello-world, since it already exited). docker ps -a shows ALL containers including stopped ones — you'll see your hello-world container listed there with status 'Exited'.
06
Containers are NOT deleted automatically when they stop (by default) — they just stop running, but their filesystem and metadata stick around until you docker rm them. This surprises beginners who expect a stopped container to simply vanish.

In your stack

→
Once Docker is installed, the very next practical step for a Java developer is usually: docker run -it eclipse-temurin:17-jdk bash — this drops you into a shell INSIDE a container that has a full JDK 17 installed, with zero local Java installation required on your host machine at all. Try it as your second command after hello-world.

Code & diagrams

install.shmarkdown

Pick the section for your OS — you only need one of these.

# ── Windows ──────────────────────────────────────────────────
# Download and run "Docker Desktop for Windows" from docker.com,
# or install it from the command line with winget:
winget install Docker.DockerDesktop
# Requires WSL2 (Docker Desktop's installer offers to enable it for you
# if it isn't already). After installing, launch Docker Desktop from the
# Start menu and wait for the whale icon in the system tray to stop animating
# — that's your signal the daemon has finished starting.

# ── macOS ────────────────────────────────────────────────────
# Download "Docker Desktop for Mac" from docker.com, or via Homebrew:
brew install --cask docker
# Then launch Docker.app from Applications (or Spotlight) — same as Windows,
# wait for the whale icon in the menu bar to stop animating.

# ── Linux (Ubuntu/Debian example) ───────────────────────────
# Official convenience script — installs Docker Engine directly, no GUI needed:
curl -fsSL https://get.docker.com | sh
# Optional but recommended: run docker without typing sudo every time
sudo usermod -aG docker $USER
# Log out and back in (or run 'newgrp docker') for the group change to take effect

first-commands.shmarkdown

Run these in order, on whichever OS you installed on. Read every line of output the first time.

# 1. Confirm the CLI is installed
docker --version

# 2. Confirm the daemon is running and reachable
docker info

# 3. The classic first container — exercises the full pull+run flow
docker run hello-world

# 4. See it in the list of ALL containers (including stopped ones)
docker ps -a

# 5. See only RUNNING containers (should be empty right now)
docker ps

# 6. Try a real, interactive container: a JDK 17 shell, no local Java needed
docker run -it eclipse-temurin:17-jdk bash
# inside the container:
java -version
exit

Explain it without notes

You run docker ps right after docker run hello-world finishes and see an EMPTY list. You then run docker ps -a and see one entry. Explain exactly why.

A teammate gets 'Cannot connect to the Docker daemon' when running any docker command. What are the two most likely causes, in order of likelihood?

Practice

Run docker run -it eclipse-temurin:17-jdk bash, then inside the container run java -version, then exit. Afterward, run docker ps -a and find this container in the list — note its exit reason.

Run docker run hello-world a SECOND time and time how much faster it feels than the first run. Explain why, using Topic 0.3's architecture.

Trade-offs

↔
Docker Desktop is the easiest on-ramp but consumes background resources (that hidden Linux VM on Windows/Mac) even when idle — on a resource-constrained machine, some developers prefer a lighter-weight alternative (like Colima on Mac, or running Docker Engine directly inside WSL2 on Windows) once they're past the beginner stage.

Done when you can

I have Docker installed and docker info succeeds without errors.
I've run hello-world and can explain every line it printed.
I understand the difference between docker ps and docker ps -a.

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