How to clean up all unused Docker images

Introduction

Docker is a powerful containerization technology that has revolutionized the way we develop, deploy, and manage applications. As you work with Docker, you may accumulate a significant number of unused images, which can consume valuable storage space on your system. In this tutorial, we will guide you through the process of identifying and removing these unused Docker images, ensuring your system remains optimized and efficient.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL docker(("`Docker`")) -.-> docker/ImageOperationsGroup(["`Image Operations`"]) docker(("`Docker`")) -.-> docker/SystemManagementGroup(["`System Management`"]) docker/ImageOperationsGroup -.-> docker/rmi("`Remove Image`") docker/ImageOperationsGroup -.-> docker/images("`List Images`") docker/ImageOperationsGroup -.-> docker/search("`Search Images in Repository`") docker/SystemManagementGroup -.-> docker/prune("`Remove Unused Docker Objects`") docker/ImageOperationsGroup -.-> docker/save("`Save Image`") docker/ImageOperationsGroup -.-> docker/load("`Load Image`") subgraph Lab Skills docker/rmi -.-> lab-417889{{"`How to clean up all unused Docker images`"}} docker/images -.-> lab-417889{{"`How to clean up all unused Docker images`"}} docker/search -.-> lab-417889{{"`How to clean up all unused Docker images`"}} docker/prune -.-> lab-417889{{"`How to clean up all unused Docker images`"}} docker/save -.-> lab-417889{{"`How to clean up all unused Docker images`"}} docker/load -.-> lab-417889{{"`How to clean up all unused Docker images`"}} end

Understanding Docker Images

Docker is a popular containerization platform that allows developers to package their applications and all their dependencies into a single, portable container. These containers can be easily deployed, scaled, and managed across different environments, making the development and deployment process more efficient and consistent.

At the heart of Docker are Docker images, which serve as the building blocks for creating containers. A Docker image is a read-only template that contains the application code, libraries, dependencies, and any other files needed to run the application. These images are typically built using a Dockerfile, which is a text-based script that defines the steps to create the image.

When a Docker image is run, it creates a Docker container, which is a running instance of the image. Containers are isolated, lightweight, and portable, ensuring that the application runs consistently across different environments.

Understanding the basics of Docker images is crucial for effectively managing and maintaining your Docker-based applications. This includes understanding how to create, manage, and optimize Docker images to ensure efficient resource utilization and minimize the storage footprint on your system.

graph TD A[Docker Image] --> B[Docker Container] B --> C[Application] B --> D[Dependencies] B --> E[OS]

Table 1: Key Characteristics of Docker Images

Characteristic	Description
Layered Structure	Docker images are built using a layered file system, where each layer represents a change made to the image. This allows for efficient storage and sharing of common layers between images.
Immutability	Docker images are designed to be immutable, meaning that once an image is created, it cannot be modified. If you need to make changes, you must create a new image.
Portability	Docker images can be easily shared and deployed across different environments, ensuring consistent application behavior.
Caching	Docker uses caching to speed up the build process, reusing layers from previous builds whenever possible.

By understanding the fundamentals of Docker images, you'll be better equipped to manage and optimize your Docker-based applications, ensuring efficient resource utilization and reliable deployments.

Identifying Unused Docker Images

As you continue to build and deploy your Docker-based applications, you may end up with a growing number of Docker images on your system. Over time, some of these images may become unused or obsolete, taking up valuable storage space. To effectively manage your Docker images, it's important to identify and remove any unused images.

Listing Docker Images

The first step in identifying unused Docker images is to list all the images currently available on your system. You can do this using the docker images command:

docker images

This will display a list of all the Docker images, including their repository, tag, image ID, creation time, and size.

Identifying Unused Images

To identify unused Docker images, you can use the following strategies:

Dangling Images: Dangling images are those that are not tagged with a specific version and are not referenced by any container. You can identify these images using the following command:
```
docker images -f dangling=true
```
Unused Images: Images that are not currently being used by any running or stopped containers can be considered unused. You can list these images using the following command:
```
docker images --filter "dangling=false" --filter "reference='*/*:*'" --format "{{.Repository}}:{{.Tag}} {{.ID}} {{.Size}}"
```
This command filters out the dangling images and displays the remaining images, along with their repository, tag, ID, and size.
Unused Images by Time: You can also identify unused images based on their creation time. For example, to list images that haven't been used for more than 30 days, you can use the following command:
```
docker images --filter "dangling=false" --filter "reference='*/*:*'" --format "{{.Repository}}:{{.Tag}} {{.ID}} {{.CreatedAt}}" | grep -v "$(date -d '30 days ago' '+%Y-%m-%d')"
```
This command filters out the dangling images, displays the remaining images with their repository, tag, ID, and creation time, and then filters out the images that were created within the last 30 days.

By using these strategies, you can effectively identify the unused Docker images on your system, which will help you to free up valuable storage space and maintain a clean and efficient Docker environment.

Removing Unused Docker Images

After identifying the unused Docker images on your system, the next step is to remove them. This will help you free up valuable storage space and maintain a clean and efficient Docker environment.

Removing Dangling Images

To remove dangling images, you can use the following command:

docker image prune

This command will remove all dangling images, which are images that are not tagged and are not referenced by any container.

Removing Unused Images

To remove unused Docker images, you can use the following command:

docker image rm <image_id>

Replace <image_id> with the ID of the image you want to remove. You can also use the image name and tag, like this:

docker image rm <image_name>:<image_tag>

If you want to remove multiple unused images at once, you can use the following command:

docker image rm $(docker images --filter "dangling=false" --filter "reference='*/*:*'" --format "{{.ID}}")

This command will remove all unused images that are not dangling.

Removing Images by Time

If you want to remove images that haven't been used for a certain period of time, you can use the following command:

docker image prune --filter "until=30d"

This command will remove all images that haven't been used for the last 30 days.

Automating Image Cleanup

To automate the process of cleaning up unused Docker images, you can create a script or a cron job that periodically runs the necessary commands. Here's an example script that you can use:

#!/bin/bash

## Remove dangling images
docker image prune -f

## Remove unused images
docker image rm $(docker images --filter "dangling=false" --filter "reference='*/*:*'" --format "{{.ID}}")

## Remove images older than 30 days
docker image prune -a --filter "until=30d" -f

Save this script as a file (e.g., clean_images.sh) and make it executable with the following command:

chmod +x clean_images.sh

You can then run the script manually or set up a cron job to run it automatically on a regular schedule.

By following these steps, you can effectively remove unused Docker images and maintain a clean and efficient Docker environment.

Summary

By following the steps outlined in this tutorial, you will be able to effectively clean up all unused Docker images on your system. This process will help you reclaim valuable storage space, improve system performance, and maintain a well-organized Docker environment. With a thorough understanding of Docker image management, you can ensure your development and deployment workflows remain efficient and streamlined.