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.

Practice

1. What is the main purpose of installing Docker on your computer?

easy

A. To create spreadsheets

B. To edit text files

C. To run applications inside containers

D. To browse the internet

Solution

1. Step 1: Understand Docker's role

   Docker is a tool that allows running applications inside isolated containers.

2. Step 2: Compare options

   Only To run applications inside containers describes running apps in containers, which is Docker's main use.

3. Final Answer:

   To run applications inside containers -> Option C

4. Quick Check:

   Docker runs apps in containers = D [OK]

Hint: Docker runs apps in containers, not for editing or browsing [OK]

Common Mistakes:

• Confusing Docker with text editors or browsers
• Thinking Docker is for general software installation
• Assuming Docker manages spreadsheets

2. Which command correctly checks the installed Docker version after installation?

easy

A. version docker --check

B. docker version check

C. check docker version

D. docker --version

Solution

1. Step 1: Recall Docker version command syntax

   The correct command to check Docker version is docker --version.

2. Step 2: Eliminate incorrect syntax

   Other options do not follow Docker CLI syntax and will cause errors.

3. Final Answer:

   docker --version -> Option D

4. Quick Check:

   Correct Docker version command = A [OK]

Hint: Use 'docker --version' to check Docker version quickly [OK]

Common Mistakes:

• Using incorrect command order or words
• Omitting double dashes before 'version'
• Trying non-Docker commands to check version

3. After running docker --version, you see this output:

Docker version 24.0.2, build cb74dfc

What does this output tell you?

medium

A. Docker is installed and working

B. Docker is not installed

C. Docker installation failed

D. Docker needs to be updated

Solution

1. Step 1: Interpret the version output

   The output shows Docker's version number and build info, meaning Docker is installed.

2. Step 2: Understand what output means

   If Docker was not installed or failed, the command would error or show no version.

3. Final Answer:

   Docker is installed and working -> Option A

4. Quick Check:

   Version output means Docker works = C [OK]

Hint: Version output means Docker installed correctly [OK]

Common Mistakes:

• Thinking version output means failure
• Confusing version info with error messages
• Assuming update needed without checking latest version

4. You tried to install Docker on Ubuntu with sudo apt install docker but got an error. What is the likely fix?

medium

A. Use sudo apt install docker.io instead

B. Run docker --version again

C. Restart the computer and try again

D. Install Docker using yum command

Solution

1. Step 1: Understand Ubuntu package naming

   On Ubuntu, the Docker package is named docker.io, not just docker.

2. Step 2: Correct the install command

   Using sudo apt install docker.io installs Docker properly on Ubuntu.

3. Final Answer:

   Use sudo apt install docker.io instead -> Option A

4. Quick Check:

   Ubuntu Docker package = docker.io = A [OK]

Hint: Ubuntu Docker package is 'docker.io', not 'docker' [OK]

Common Mistakes:

• Trying to install 'docker' package which doesn't exist
• Using wrong package manager commands
• Ignoring error messages without checking package name

5. You want to install Docker on Windows using the official installer. Which step should you do first?

medium

A. Run sudo apt install docker in PowerShell

B. Download Docker Desktop from the official Docker website

C. Open Command Prompt and type docker run

D. Install VirtualBox before Docker

Solution

1. Step 1: Identify Windows installation method

   Windows users install Docker using Docker Desktop downloaded from Docker's official site.

2. Step 2: Eliminate incorrect steps

   Linux commands like sudo apt install don't work on Windows; VirtualBox is not required.

3. Final Answer:

   Download Docker Desktop from the official Docker website -> Option B

4. Quick Check:

   Windows Docker install starts with official Docker Desktop download = B [OK]

Hint: Windows Docker install starts with official Docker Desktop download [OK]

Common Mistakes:

• Trying Linux commands on Windows
• Assuming VirtualBox is needed for Docker
• Running Docker commands before installation