Installing Docker - Practice Exercises

Challenge - 5 Problems

💻 Command Output

intermediate

Docker Installation Verification

After installing Docker on a Linux system, you run the command docker --version. What is the expected output format?

Docker

docker --version

A Version: 24.0.2

B docker: command not found

C Docker version 24.0.2, build abc1234

D Error: Docker daemon not running

💡 Hint

The command shows the installed Docker version and build info.

The docker --version command outputs the Docker version and build number in a specific format like 'Docker version 24.0.2, build abc1234'. Other outputs indicate errors or missing installation.

🧠 Conceptual

intermediate

Docker Installation Prerequisites

Which of the following is a necessary prerequisite before installing Docker on a Linux system?

A Installing Node.js first

B Having a 64-bit operating system

C Disabling all firewalls

D Installing Java Runtime Environment

💡 Hint

Docker requires a specific OS architecture to run.

Docker requires a 64-bit OS to run properly. Node.js, Java, or disabling firewalls are not prerequisites for Docker installation.

❓ Configuration

advanced

Docker Repository Setup on Ubuntu

Which command correctly adds the official Docker repository key on Ubuntu before installing Docker?

A sudo add-apt-repository ppa:docker/stable

B wget -qO - https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

C sudo apt-get install docker-ce

D curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

💡 Hint

The official Docker docs recommend using gpg with dearmor for keyring.

Option D correctly downloads and adds the Docker GPG key in the recommended keyring location. Option D uses deprecated apt-key. Option D installs Docker but does not add the key. Option D is invalid for Docker.

❓ Troubleshoot

advanced

Docker Daemon Not Starting

After installing Docker, the command sudo systemctl start docker fails with the error: Failed to start docker.service: Unit docker.service not found. What is the most likely cause?

A Docker package was not installed correctly

B The user does not have sudo privileges

C The Docker daemon is already running

D The system is missing internet connection

💡 Hint

The error means the system cannot find the Docker service unit file.

If the service unit file is missing, it usually means Docker was not installed properly. Lack of sudo or internet would cause different errors. If daemon was running, start would not fail with 'not found'.

🔀 Workflow

expert

Correct Docker Installation Steps on CentOS

What is the correct order of commands to install Docker on CentOS 8?

A 1,2,3,4

B 2,1,3,4

C 1,3,2,4

D 3,1,2,4

💡 Hint

First add repo, then install packages, then start and enable service.

The correct workflow is to add the Docker repo first, install Docker packages next, then start the Docker service and enable it to start on boot.