System prune for cleanup in Docker - Commands & Configuration

Introduction

Sometimes your computer fills up with unused Docker data like stopped containers, unused images, and networks. This can slow things down or waste space. The system prune command helps clean up all this unused data in one go.

When your disk space is low and you want to free up space used by Docker.

After testing many containers and images that you no longer need.

When you want to remove all stopped containers and unused images to keep your system tidy.

Before backing up your system to reduce the backup size.

When Docker commands become slow due to too many leftover resources.

Commands

This command removes all stopped containers, unused networks, dangling images, and build cache without asking for confirmation because of the -f flag.

Terminal

docker system prune -f

Expected Output

Deleted Containers:

<container_id_1>

Deleted Images:

<image_id_1>

Deleted Networks:

<network_id_1>

Total reclaimed space: 500MB

→

-f - Force the prune without confirmation prompt

This command shows how much disk space Docker is using before and after cleanup to verify the prune worked.

Terminal

docker system df

Expected Output

TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE

Images          10        2         2.5GB     1.5GB (60%)

Containers      5         1         300MB     200MB (66%)

Local Volumes   3         3         1GB       0B (0%)

Build Cache     0         0         0B        0B

Key Concept

If you remember nothing else from this pattern, remember: docker system prune cleans up all unused Docker data to free disk space quickly.

Common Mistakes

Running docker system prune without the -f flag and then not confirming the prompt.

The command waits for user confirmation and does nothing until you type 'y'.

Use the -f flag to skip the confirmation if you want to automate or speed up the cleanup.

Expecting docker system prune to remove all images including those used by running containers.

It only removes dangling and unused images, not images used by running containers.

Stop and remove containers first if you want to remove their images.

Summary

Use docker system prune -f to remove all stopped containers, unused networks, dangling images, and build cache.

Check disk space usage before and after cleanup with docker system df.

Add the -f flag to avoid confirmation prompts during cleanup.