20250405 Deck2

Question 1

What does docker-ce provide that docker-ce-cli does not?

Answer 1

docker-ce installs the Docker Engine (daemon), which actually runs containers. docker-ce-cli only provides the command-line interface. Without docker-ce, you can’t run containers.

Question 2

Why is it important to add Docker’s official GPG key and repository instead of using Ubuntu’s default Docker packages?

Answer 2

The official repo provides the latest stable Docker version. The GPG key verifies that packages are authentic and safe. Ubuntu’s default packages may be outdated or incomplete.

Question 3

What does sudo usermod -aG docker $USER do, and why is it followed by newgrp docker or logout?

Answer 3

It adds your user to the docker group, allowing you to run Docker commands without sudo. newgrp docker (or logout/login) applies the group change.

Question 4

What is the purpose of the ca-certificates package on Linux?

Answer 4

It provides trusted Certificate Authority certificates used for verifying HTTPS connections. Without it, secure downloads and communications might fail.

Question 5

What is the difference between docker-compose and docker compose?

Answer 5

docker-compose is the older v1 (Python-based). docker compose is the newer v2+ (plugin-based) built into the Docker CLI. v2+ is actively maintained and preferred.

Question 6

What is the difference between systemctl start docker and systemctl enable docker?

Answer 6

start runs the Docker service immediately. enable makes Docker auto-start on boot.

Question 7

If you get ‘Failed to enable unit: Unit file docker.service does not exist,’ what’s likely missing?

Answer 7

The docker-ce package (Docker Engine) is missing. Install it with sudo apt install docker-ce containerd.io.

Question 8

How do you test if Docker and Docker Compose are working correctly?

Answer 8

Use docker run hello-world to test Docker, and docker compose version to test Compose.

Question 9

What are the risks of not adding yourself to the Docker group and always using sudo for Docker?

Answer 9

Using sudo is more secure but less convenient. Adding yourself to the Docker group allows password-free Docker use, but users in that group have root-like access.

Question 10

What are the key components installed when setting up Docker on Linux, and what do they do?

Answer 10

• docker-ce: Docker Engine (core daemon)
• docker-ce-cli: Command-line interface
• containerd.io: Low-level container runtime
• docker-compose-plugin: Plugin for Docker Compose v2+