Container disk usage management in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What command shows the disk space used by Docker images, containers, volumes, and build cache?

The command docker system df displays disk usage by Docker images, containers, volumes, and build cache.

beginner

How can you remove all stopped containers to free up disk space?

Use docker container prune to remove all stopped containers and free disk space.

intermediate

What does the command docker image prune -a do?

It removes all unused images, including dangling and unreferenced images, freeing disk space.

beginner

Why should you manage Docker volumes regularly?

Unused volumes can take up disk space. Running docker volume prune removes unused volumes to save space.

intermediate

What is the effect of docker system prune?

It removes stopped containers, unused networks, dangling images, and build cache to free disk space.

Which command shows detailed disk usage of Docker resources?

A docker system df

B docker ps

C docker images

D docker info

docker system df shows disk usage details for images, containers, volumes, and cache.

How do you remove all stopped containers at once?

A docker rm -f

B docker container prune

C docker image prune

D docker volume prune

docker container prune removes all stopped containers safely.

What does docker image prune -a remove?

A Only dangling images

B All volumes

C All containers

D All unused images

The -a flag removes all unused images, not just dangling ones.

Which command removes unused Docker volumes?

A docker system prune

B docker volume rm

C docker volume prune

D docker container prune

docker volume prune removes all unused volumes to free disk space.

What does docker system prune NOT remove by default?

A Running containers

B Unused networks

C Dangling images

D Stopped containers

Running containers are not removed by docker system prune.

Explain how to check and clean up disk space used by Docker containers, images, and volumes.

Think about commands that show usage and commands that remove unused resources.

Describe the difference between removing dangling images and all unused images in Docker.

Focus on the meaning of dangling vs unused images and the prune command flags.

Practice

1. What does the docker system df command show you?

easy

A. The disk space used by Docker images, containers, and volumes

B. The list of running Docker containers

C. The network settings of Docker containers

D. The logs of a specific Docker container

Solution

1. Step 1: Understand the purpose of docker system df and compare options

   This command summarizes disk usage by Docker objects like images, containers, and volumes. Options B (docker ps), C (network settings), and D (logs) describe unrelated commands.

2. Final Answer:

   The disk space used by Docker images, containers, and volumes -> Option A

3. Quick Check:

   Disk usage summary = A [OK]

Hint: Remember 'df' means disk free or usage summary [OK]

Common Mistakes:

• Confusing disk usage with container status
• Thinking it shows logs or network info
• Using it to list running containers

2. Which of the following commands correctly removes only all stopped containers to free disk space?

easy

A. docker container prune

B. docker image rm $(docker images -q)

C. docker system prune -a

D. docker container rm -f $(docker ps -a -q)

Solution

1. Step 1: Identify command to remove only stopped containers and check options

   docker container prune safely removes all stopped containers only. A forcibly removes all containers (running and stopped). B removes images. C removes stopped containers plus unused images and networks (more than containers).

2. Final Answer:

   docker container prune -> Option A

3. Quick Check:

   Remove stopped containers = D [OK]

Hint: Use prune commands to safely clean stopped containers [OK]

Common Mistakes:

• Using force remove on all containers including running ones
• Confusing image removal with container removal
• Using system prune when only containers should be removed

3. What will be the output of the command docker system df after running docker image prune -a?

medium

A. Error message about running containers

B. Disk usage report showing fewer images and freed space

C. List of all images including unused ones

D. No change in disk usage report

Solution

1. Step 1: Understand docker image prune -a effect on docker system df

   This removes all unused images, freeing space, so the report shows fewer images and more free space. No error, no list, and usage changes.

2. Final Answer:

   Disk usage report showing fewer images and freed space -> Option B

3. Quick Check:

   Image prune frees space = B [OK]

Hint: Prune unused images to reduce disk usage [OK]

Common Mistakes:

• Expecting an error when pruning images
• Thinking prune lists images instead of removing
• Assuming no change in disk usage after prune

4. You ran docker volume prune but still see high disk usage. What could be the reason?

medium

A. The prune command only cleans network settings

B. The prune command deleted running containers by mistake

C. Docker does not track volume disk usage

D. There are unused images and stopped containers still taking space

Solution

1. Step 1: Understand docker volume prune and reason for remaining usage

   It removes unused volumes only. Unused images and stopped containers remain, causing high usage. No deletion of running containers or network cleaning.

2. Final Answer:

   There are unused images and stopped containers still taking space -> Option D

3. Quick Check:

   Volume prune only removes volumes = A [OK]

Hint: Prune volumes only frees volume space, check images and containers too [OK]

Common Mistakes:

• Assuming volume prune deletes containers
• Thinking prune affects network settings
• Believing Docker ignores volume disk usage

5. You want to free maximum disk space but keep your running containers and their data intact. Which command should you use?

hard

A. docker container rm -f $(docker ps -q)

B. docker system prune --volumes

C. docker system prune -a --volumes

D. docker image rm $(docker images -q)

Solution

1. Step 1: Analyze options for maximum safe cleanup

   docker system prune -a --volumes removes all stopped containers, all unused images (not just dangling), unused networks, and unused volumes--maximizing space--while keeping running containers and their data intact. C frees less (no -a). A removes running containers. D only images, unsafely and incompletely.

2. Final Answer:

   docker system prune -a --volumes -> Option C

3. Quick Check:

   Max prune safely, keep running containers = B [OK]

Hint: Use system prune with volumes to clean safely without stopping containers [OK]

Common Mistakes:

• Using prune without -a flag, freeing less space
• Force removing running containers causing downtime
• Removing images only without cleaning volumes or containers