Removing images in Docker - Step-by-Step Execution

Process Flow - Removing images

List images

↓

Choose image to remove

↓

Run docker rmi command

↓

Check if image removed

↓

Success or error message

The flow shows listing images, selecting one, removing it with a command, and verifying removal.

Execution Sample

Docker

docker images
# Lists all images

docker rmi alpine:latest
# Removes the alpine image

docker images
# Lists images again to confirm removal

This sequence lists images, removes the alpine image, then lists images again to confirm it is gone.

Process Table

Step	Command	Action	Result	Output
1	docker images	List all images	Images listed	REPOSITORY TAG IMAGE ID CREATED SIZE alpine latest abc123def456 2 weeks ago 5MB ubuntu 20.04 def456abc123 3 weeks ago 72MB
2	docker rmi alpine:latest	Remove alpine image	Image removed	Untagged: alpine:latest Deleted: sha256:abc123def456
3	docker images	List images again	Alpine image gone	REPOSITORY TAG IMAGE ID CREATED SIZE ubuntu 20.04 def456abc123 3 weeks ago 72MB

💡 Alpine image removed successfully, no longer listed.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
Images List	[]	[alpine:latest, ubuntu:20.04]	[ubuntu:20.04]	[ubuntu:20.04]

Key Moments - 2 Insights

Why does the image still appear if I try to remove it but get an error?

If the image is used by a running container, removal fails. See step 2 output for errors. You must stop containers first.

What happens if I remove an image tag but the image has multiple tags?

Only the specified tag is removed (untagged). The image stays if other tags exist. Step 2 shows 'Untagged' message.

Visual Quiz - 3 Questions

Look at the execution table, what images are listed after step 1?

A Only ubuntu:20.04

B alpine:latest and ubuntu:20.04

C No images listed

D Only alpine:latest

💡 Hint

Check the Output column in step 1 of the execution_table.

At which step is the alpine image removed from the list?

A Step 1

B Step 3

C Step 2

D It is never removed

💡 Hint

Look at the Action and Result columns in step 2.

If you tried to remove an image used by a running container, what would happen?

A Command fails with error

B Image is removed anyway

C Image is renamed

D Image is paused

💡 Hint

Refer to key_moments about removal errors when containers use the image.

Concept Snapshot

docker images - lists all images

docker rmi <image> - removes specified image

Removal fails if image is used by containers

Check images again to confirm removal

Use docker ps to stop containers before removal

Full Transcript

This visual execution shows how to remove Docker images step-by-step. First, you list all images with 'docker images'. Then you remove a chosen image using 'docker rmi <image>'. Finally, you list images again to confirm the removal. The execution table tracks commands, actions, and outputs. The variable tracker shows how the images list changes after each step. Key moments explain common confusions like removal errors if containers use the image. The quiz tests understanding of image listing, removal step, and error cases. The snapshot summarizes the commands and rules for removing images.

Practice

1. What is the basic Docker command to remove an image from your system?

easy

A. docker delete <image_name_or_id>

B. docker rmi <image_name_or_id>

C. docker remove image <image_name_or_id>

D. docker rm <image_name_or_id>

Solution

1. Step 1: Understand Docker image removal command

   The correct command to remove Docker images is docker rmi. It stands for 'remove image'.

2. Step 2: Identify the correct syntax

   The command requires the image name or ID after docker rmi to specify which image to remove.

3. Final Answer:

   docker rmi <image_name_or_id> -> Option B

4. Quick Check:

   Remove image = docker rmi [OK]

Hint: Use 'docker rmi' to remove images quickly [OK]

Common Mistakes:

• Using 'docker rm' which removes containers, not images
• Typing 'docker delete' which is not a valid Docker command
• Confusing image removal with container removal commands

2. Which of the following is the correct syntax to force remove a Docker image named myapp:latest?

easy

A. docker rmi -f myapp:latest

B. docker rmi -force myapp:latest

C. docker rmi -rf myapp:latest

D. docker rmi --f myapp:latest

Solution

1. Step 1: Identify the correct flag for force removal

   The short flag -f is used to force remove images in Docker.

2. Step 2: Confirm the correct command syntax

   The correct command is docker rmi -f myapp:latest. Other options use invalid flags like -rf, -force, or --f.

3. Final Answer:

   docker rmi -f myapp:latest -> Option A

4. Quick Check:

   Force remove = docker rmi -f [OK]

Hint: Use '-f' to force remove images safely [OK]

Common Mistakes:

• Using incorrect flag like '-rf', '-force' or '--f'
• Confusing force flag with other options
• Misspelling the flag causing command failure

3. What will be the output of the command docker rmi 123abc456def if the image ID 123abc456def exists and is not used by any container?

medium

A. Image removed but container still running

B. Error: image is being used by a running container

C. No such image: 123abc456def

D. Untagged: 123abc456def
Deleted: sha256:123abc456def...

Solution

1. Step 1: Check if image exists and is unused

   If the image ID exists and no container uses it, Docker removes it cleanly.

2. Step 2: Understand Docker rmi output

   The command outputs lines showing the image is untagged and deleted with its sha256 hash.

3. Final Answer:

   Untagged: 123abc456def Deleted: sha256:123abc456def... -> Option D

4. Quick Check:

   Image removed cleanly = Untagged: 123abc456def Deleted: sha256:123abc456def... [OK]

Hint: If image unused, 'docker rmi' shows untagged and deleted [OK]

Common Mistakes:

• Assuming image removal works if container uses it
• Expecting no output on successful removal
• Confusing image ID with container ID

4. You run docker rmi myimage but get the error: Error response from daemon: conflict: unable to delete image (must be forced) - image is being used by running container. What should you do to fix this?

medium

A. Use docker rm myimage to remove the image

B. Run docker rmi myimage again without changes

C. Stop the running container using the image, then run docker rmi myimage again

D. Restart Docker daemon and try again

Solution

1. Step 1: Understand the error meaning

   The error says the image is used by a running container, so Docker won't remove it without force.

2. Step 2: Stop the container using the image

   You must stop or remove the container using the image before removing the image itself.

3. Final Answer:

   Stop the running container using the image, then run docker rmi myimage again -> Option C

4. Quick Check:

   Stop container before removing image [OK]

Hint: Stop containers using image before removal [OK]

Common Mistakes:

• Trying to remove image without stopping containers
• Using 'docker rm' which removes containers, not images
• Restarting Docker daemon unnecessarily

5. You want to remove all Docker images that are not used by any container to free up space. Which command will safely do this?

hard

A. docker image prune -a

B. docker rmi $(docker images -q)

C. docker rmi -f $(docker ps -aq)

D. docker container prune

Solution

1. Step 1: Understand the goal

   You want to remove all unused images, but keep images used by containers.

2. Step 2: Identify the correct command

   docker image prune -a removes all unused images safely without affecting running containers.

3. Step 3: Analyze other options

   docker rmi $(docker images -q) tries to remove all images, including used ones, causing errors.
   docker rmi -f $(docker ps -aq) is invalid because docker ps -aq lists containers, not images.
   docker container prune removes stopped containers, not images.

4. Final Answer:

   docker image prune -a -> Option A

5. Quick Check:

   Remove unused images safely = docker image prune -a [OK]

Hint: Use 'docker image prune -a' to clean unused images [OK]

Common Mistakes:

• Trying to remove all images forcibly causing errors
• Confusing container prune with image prune
• Using container IDs instead of image IDs in commands