Listing local images in Docker - Step-by-Step Execution

Process Flow - Listing local images

Run 'docker images'

↓

Docker CLI sends request

↓

Docker daemon fetches local images

↓

Daemon returns image list

↓

CLI displays images in table format

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Done

The command 'docker images' asks Docker to show all local images. Docker daemon fetches and returns the list, then CLI shows it.

Execution Sample

Docker

docker images

This command lists all Docker images stored locally on your machine.

Process Table

Step	Action	Docker CLI Output	Result
1	User types 'docker images' and presses Enter		Command sent to Docker daemon
2	Docker daemon retrieves local images		Fetches image metadata
3	Docker CLI receives image list	REPOSITORY TAG IMAGE ID CREATED SIZE	Ready to display
4	Docker CLI displays images	ubuntu latest 2ca708c1c9cc 2 weeks ago 72.9MB	Image info shown
5	Docker CLI displays images	nginx stable 4bb46517cac3 3 weeks ago 133MB	Image info shown
6	Docker CLI displays images	hello-world latest fce289e99eb9 5 months ago 13.3kB	Image info shown
7	End of list reached		Command completes

💡 All local images listed and displayed, command ends.

Status Tracker

Variable	Start	After Step 2	After Step 3	Final
local_images	empty	fetched list of images metadata	list passed to CLI	displayed to user

Key Moments - 2 Insights

Why do I see multiple images with the same repository name?

Each row shows a different tag or version of the image. See execution_table rows 4-6 where repository 'ubuntu', 'nginx', and 'hello-world' have different tags.

What does the IMAGE ID represent?

IMAGE ID is a unique short identifier for each image version. It helps Docker track images internally, shown in execution_table rows 4-6.

Visual Quiz - 3 Questions

Look at the execution_table row 4, what is the TAG of the 'ubuntu' image?

A latest

B stable

C fce289e99eb9

D 2 weeks ago

💡 Hint

Check the 'Docker CLI Output' column in row 4 for the 'ubuntu' image tag.

At which step does the Docker CLI start displaying the image list?

A Step 2

B Step 4

C Step 3

D Step 7

💡 Hint

Look for the first row where 'Docker CLI displays images' in the 'Action' column.

If there are no images locally, what would the output be after step 2?

A List of images with zero size

B Error message

C An empty list with only headers

D Command hangs

💡 Hint

Docker shows headers even if no images exist, so check what 'local_images' would be in variable_tracker.

Concept Snapshot

docker images
Lists all local Docker images.
Shows repository, tag, image ID, creation date, and size.
Useful to see what images are stored locally.
No arguments needed for basic listing.

Full Transcript

The 'docker images' command lists all Docker images stored locally. When you run it, the Docker CLI sends a request to the Docker daemon. The daemon fetches metadata about all local images and sends it back. The CLI then displays this information in a table showing repository names, tags, image IDs, creation dates, and sizes. Each image can have multiple tags representing different versions. The IMAGE ID uniquely identifies each image. If no images exist, the command shows only the table headers. This command helps you see what images are available on your machine.

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