Verifying installation with docker run hello-world - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the command docker run hello-world do?

It downloads a test image called 'hello-world' from Docker Hub and runs it to verify that Docker is installed and working correctly on your system.

beginner

Why is the hello-world image used to verify Docker installation?

Because it is a small, simple image designed to print a confirmation message, showing Docker can pull images and run containers successfully.

beginner

What output should you expect after running docker run hello-world if Docker is installed correctly?

You should see a message starting with 'Hello from Docker!' followed by information about Docker and instructions for next steps.

beginner

What happens if Docker is not installed or not running when you run docker run hello-world?

You will get an error message indicating Docker is not found or the Docker daemon is not running, meaning the installation or service needs to be fixed.

beginner

How does docker run hello-world help beginners?

It provides a quick, easy way to confirm Docker is set up correctly without needing to write any code or complex commands.

What is the purpose of running docker run hello-world?

A To update Docker to the latest version

B To start a web server

C To verify Docker installation and functionality

D To remove all Docker images

The command runs a simple container that confirms Docker is installed and working.

What should you see if docker run hello-world runs successfully?

A A message starting with 'Hello from Docker!'

B A list of all Docker containers

C An error message about missing images

D A prompt to enter Docker commands

The hello-world image prints a welcome message confirming Docker works.

If Docker is not running, what happens when you run docker run hello-world?

A You get an error about Docker daemon not running

B The hello-world container runs anyway

C Docker automatically starts the daemon

D The command updates Docker

Docker requires its daemon to be running to execute containers.

Where does Docker get the 'hello-world' image from if it is not on your computer?

A Your local file system

B Docker Hub (online image repository)

C It creates the image automatically

D From your operating system

Docker pulls images from Docker Hub if they are not found locally.

Which command confirms Docker is installed and working correctly?

A docker build .

B docker ps -a

C docker stop all

D docker run hello-world

The 'hello-world' container is designed to verify Docker installation.

Explain how the command docker run hello-world verifies your Docker installation.

Think about what happens behind the scenes when you run the command.

Describe what you should do if running docker run hello-world gives an error.

Focus on troubleshooting Docker service and installation.

Practice

1. What does the command docker run hello-world do?

easy

A. It lists all running Docker containers.

B. It updates Docker to the latest version.

C. It removes all Docker containers from the system.

D. It downloads and runs a test container to verify Docker installation.

Solution

1. Step 1: Understand the command purpose

   The command docker run hello-world pulls a small test image from Docker Hub if not present and runs it.

2. Step 2: Observe the output

   The container prints a confirmation message indicating Docker is installed and working correctly.

3. Final Answer:

   It downloads and runs a test container to verify Docker installation. -> Option D

4. Quick Check:

   docker run hello-world = verify Docker installation [OK]

Hint: Remember: hello-world test confirms Docker works [OK]

Common Mistakes:

• Thinking it updates Docker
• Confusing it with container removal
• Assuming it lists containers

2. Which of the following is the correct syntax to run the hello-world Docker container?

easy

A. docker run hello-world

B. docker start hello-world

C. docker execute hello-world

D. docker build hello-world

Solution

1. Step 1: Identify the command to run a container

   The correct command to run a container is docker run followed by the image name.

2. Step 2: Match the image name

   The image name here is hello-world, so the full command is docker run hello-world.

3. Final Answer:

   docker run hello-world -> Option A

4. Quick Check:

   docker run + image name = docker run hello-world [OK]

Hint: Use 'docker run' to start containers, not 'start' or 'build' [OK]

Common Mistakes:

• Using 'docker start' which only starts stopped containers
• Using 'docker execute' which is invalid
• Using 'docker build' which builds images, not runs them

3. What output should you expect after successfully running docker run hello-world?

medium

A. No output, just a blank screen.

B. A message confirming Docker is installed and working.

C. A list of all Docker images on your system.

D. An error saying 'image not found'.

Solution

1. Step 1: Understand the purpose of the hello-world container

   This container prints a friendly message confirming Docker installation.

2. Step 2: Recognize expected output

   The output includes a welcome message and instructions confirming Docker works.

3. Final Answer:

   A message confirming Docker is installed and working. -> Option B

4. Quick Check:

   hello-world output = confirmation message [OK]

Hint: Look for confirmation text after running hello-world [OK]

Common Mistakes:

• Expecting image list instead of message
• Confusing error output with success
• Thinking no output means success

4. You run docker run hello-world but get an error: Cannot connect to the Docker daemon. What is the likely cause?

medium

A. Docker daemon is not running on your system.

B. The hello-world image does not exist.

C. You typed the command incorrectly.

D. Your internet connection is down.

Solution

1. Step 1: Analyze the error message

   The error 'Cannot connect to the Docker daemon' means the Docker service is not running or accessible.

2. Step 2: Understand Docker daemon role

   The Docker daemon manages containers; if it is stopped, commands cannot run.

3. Final Answer:

   Docker daemon is not running on your system. -> Option A

4. Quick Check:

   Docker daemon stopped = connection error [OK]

Hint: Check if Docker service is running before running containers [OK]

Common Mistakes:

• Assuming image missing causes daemon error
• Blaming command syntax without checking daemon
• Ignoring daemon status and blaming internet

5. After installing Docker, you run docker run hello-world but see a permission denied error. What should you do to fix this?

hard

A. Delete all Docker images and try again.

B. Reinstall Docker completely.

C. Run the command with elevated permissions, e.g., using sudo.

D. Restart your computer without changing anything.

Solution

1. Step 1: Understand permission denied error

   This error often means your user lacks rights to access Docker daemon.

2. Step 2: Use elevated permissions

   Running sudo docker run hello-world grants necessary rights to run the container.

3. Final Answer:

   Run the command with elevated permissions, e.g., using sudo. -> Option C

4. Quick Check:

   Permission denied fix = use sudo [OK]

Hint: Use sudo if permission denied running Docker commands [OK]

Common Mistakes:

• Reinstalling Docker unnecessarily
• Deleting images instead of fixing permissions
• Restarting without addressing permissions