Listing local images in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of the command to list all local Docker images?

You run the command docker images on a system with three images: alpine:latest, ubuntu:20.04, and nginx:1.21. What will the command output show?

Docker

docker images

A

REPOSITORY   TAG       IMAGE ID       CREATED        SIZE
alpine       latest    abc123def456   2 weeks ago    5.5MB
ubuntu       20.04     def456abc123   3 weeks ago    72.9MB
nginx        1.21      123abc456def   1 week ago     133MB

B

REPOSITORY   TAG       IMAGE ID       CREATED        SIZE
alpine       latest    abc123def456   2 weeks ago    5.5MB
ubuntu       20.04     def456abc123   3 weeks ago    72.9MB

C

REPOSITORY   TAG       IMAGE ID       CREATED        SIZE
nginx        1.21      123abc456def   1 week ago     133MB

D

REPOSITORY   TAG       IMAGE ID       CREATED        SIZE
none         none      none          none           none

💡 Hint

The docker images command lists all local images with their tags and sizes.

The docker images command shows all local images. Since there are three images, all appear in the output with their details.

🧠 Conceptual

intermediate

Which Docker command lists only image IDs of local images?

You want to see just the image IDs of all local Docker images without other details. Which command will do this?

A docker images --format "{{.ID}}"

B docker images --ids

C docker list images --id-only

D docker images -q --all

💡 Hint

Use the --format option with a Go template to customize output.

The docker images --format "{{.ID}}" command lists only the image IDs. Option A is close but -q alone lists IDs; --all is not needed here.

❓ Troubleshoot

advanced

Why does docker images show no images after pulling one?

You run docker pull nginx successfully, but then docker images shows no images. What could cause this?

A The image pull failed silently and no image was downloaded.

B You are connected to a different Docker context or daemon than where the image was pulled.

C Docker images command requires sudo privileges to show images.

D The image was pulled but immediately deleted by a cleanup process.

💡 Hint

Check if Docker is using the same context or daemon for both commands.

Docker contexts or daemons can be switched. Pulling an image in one context and listing images in another shows no images.

🔀 Workflow

advanced

What is the correct sequence to list images, remove one, then verify removal?

You want to list all images, remove the image with ID abc123, then confirm it is removed. Which sequence of commands is correct?

A 2,1,3

B 1,3,2

C 1,2,3

D 3,1,2

💡 Hint

You must list images first to see what is available before removing.

First list images to confirm the image ID, then remove it, then list again to verify removal.

✅ Best Practice

expert

Which command safely lists all local images including intermediate layers?

You want to see all local Docker images including intermediate layers that are not tagged. Which command achieves this?

A docker images --include-untagged

B docker images --filter intermediate=true

C docker images --show-intermediate

D docker images --all

💡 Hint

Use the option that shows all images, not just tagged ones.

The --all option lists all images including intermediate layers. Other options do not exist or are invalid.

Practice

1. What does the docker images command do?

easy

A. Lists all local Docker images stored on your machine

B. Shows running Docker containers

C. Deletes all Docker images

D. Builds a new Docker image from a Dockerfile

Solution

1. Step 1: Understand the purpose of docker images

   This command is designed to show all Docker images saved locally on your computer.

2. Step 2: Differentiate from other Docker commands

   Commands like docker ps show running containers, and docker build creates images, so they are not correct here.

3. Final Answer:

   Lists all local Docker images stored on your machine -> Option A

4. Quick Check:

   docker images = list local images [OK]

Hint: Remember: images = saved pictures, containers = running apps [OK]

Common Mistakes:

• Confusing images with running containers
• Thinking it deletes images
• Mixing it up with build command

2. Which of these is the correct syntax to list all local Docker images?

easy

A. docker list images

B. docker image list -a

C. docker show images

D. docker images

Solution

1. Step 1: Recall the exact command for listing images

   The standard command is docker images to list local images.

2. Step 2: Check other options for correctness

   docker list images and docker show images are invalid commands. docker image list -a is a valid command but lists all images including intermediate layers, which is more advanced than the basic listing.

3. Final Answer:

   docker images -> Option D

4. Quick Check:

   Correct syntax = docker images [OK]

Hint: Use exact command: docker images, no extra words [OK]

Common Mistakes:

• Adding extra words like 'list' or 'show'
• Using incorrect flags or subcommands
• Confusing 'image' and 'images'

3. What will be the output of the command docker images if you have two images named app with tags v1 and v2?

medium

A. It will list images but without tags

B. It will list only the latest image

C. It will list both images with their tags and IDs

D. It will show an error about duplicate image names

Solution

1. Step 1: Understand how Docker images are listed

   The docker images command shows all images, including multiple tags for the same image name.

2. Step 2: Confirm output details

   Both images named app with tags v1 and v2 will appear separately with their tags and image IDs.

3. Final Answer:

   It will list both images with their tags and IDs -> Option C

4. Quick Check:

   docker images lists all tags separately [OK]

Hint: Each tag is a separate image entry in the list [OK]

Common Mistakes:

• Assuming only one tag shows
• Expecting an error for duplicate names
• Thinking tags are hidden

4. You ran docker images -l but got an error. What is the problem?

medium

A. The -l flag is invalid for docker images

B. You need to run the command as root

C. You must specify an image name with -l

D. The Docker daemon is not running

Solution

1. Step 1: Check the meaning of -l flag

   The -l flag is not a valid option for docker images. It causes a syntax error.

2. Step 2: Consider other possible causes

   Running as root or daemon status would cause different errors. The -l flag does not require an image name.

3. Final Answer:

   The -l flag is invalid for docker images -> Option A

4. Quick Check:

   Invalid flag = error [OK]

Hint: Use only supported flags with docker images [OK]

Common Mistakes:

• Assuming -l lists latest images
• Thinking root permission fixes flag errors
• Confusing daemon errors with syntax errors

5. You want to list all local Docker images but only show the repository and tag columns. Which command should you use?

hard

A. docker images --filter "repository,tag"

B. docker images --format "{{.Repository}}:{{.Tag}}"

C. docker images --only repository tag

D. docker images --columns repository tag

Solution

1. Step 1: Understand formatting option in docker images

   The --format flag lets you customize output columns using Go template syntax.

2. Step 2: Check each option's validity

   --format "{{.Repository}}:{{.Tag}}" correctly formats output to show only repository and tag. Other options are invalid or unsupported.

3. Final Answer:

   docker images --format "{{.Repository}}:{{.Tag}}" -> Option B

4. Quick Check:

   Use --format with Go templates for custom columns [OK]

Hint: Use --format with {{.Repository}} and {{.Tag}} [OK]

Common Mistakes:

• Using unsupported flags like --only or --columns
• Confusing --filter with formatting
• Incorrect template syntax