Verifying installation with docker run hello-world - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of docker run hello-world on a fresh Docker install?

You just installed Docker and ran docker run hello-world. What output should you expect to confirm Docker is working correctly?

Docker

docker run hello-world

A A message starting with 'Hello from Docker!' followed by instructions about Docker installation verification.

B An error message saying 'docker: command not found'.

C A blank screen with no output.

D A message saying 'Cannot connect to the Docker daemon at unix:///var/run/docker.sock'.

💡 Hint

Think about what a successful Docker container run would print to confirm installation.

The 'hello-world' image prints a friendly message starting with 'Hello from Docker!' to confirm Docker is installed and running properly.

❓ Troubleshoot

intermediate

Which error indicates Docker daemon is not running when running docker run hello-world?

You run docker run hello-world but get an error. Which error message means the Docker daemon is not running?

Docker

docker run hello-world

A Error: permission denied while accessing Docker socket.

B Error: image hello-world not found locally and no pull access.

C Error: command not found: docker

D Error: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

💡 Hint

Look for the message about connecting to the Docker daemon.

The error about not connecting to the Docker daemon means the Docker service is not running or accessible.

✅ Best Practice

advanced

What is the best practice to verify Docker installation on a new machine?

After installing Docker, which step is the best practice to verify the installation?

A Restart the machine and check Docker service status only.

B Run <code>docker ps</code> to list running containers immediately after install.

C Run <code>docker run hello-world</code> to test if Docker can pull and run containers.

D Run <code>docker build .</code> in an empty directory.

💡 Hint

Think about a simple command that confirms Docker can run containers.

Running 'docker run hello-world' is the simplest way to confirm Docker is installed, the daemon is running, and containers can be pulled and executed.

🧠 Conceptual

advanced

Why does docker run hello-world download an image on first run?

When you run docker run hello-world for the first time, Docker downloads the image. Why does this happen?

A Because Docker always downloads images even if they exist locally.

B Because the image is not present locally, Docker pulls it from the default registry to run the container.

C Because the hello-world image is built locally every time you run the command.

D Because Docker needs to update the image to the latest version before running.

💡 Hint

Think about how Docker handles images it does not have on your computer.

Docker pulls images from a registry only if they are not found locally to run containers.

🔀 Workflow

expert

What is the correct sequence of steps when verifying Docker installation using docker run hello-world?

Put these steps in the correct order to verify Docker installation using the 'hello-world' image.

A 3,1,4,2

B 1,3,4,2

C 3,4,1,2

D 4,3,1,2

💡 Hint

Think about what must be ready before running the command and what happens during execution.

First, Docker daemon must be running (3). Then you run the command (1). If image missing, Docker pulls it (4). Finally, you check the output (2).

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