Cleaning up Docker - deleting images, containers and volumes

What is Docker?

Docker is a platform that allows developers to build, deploy, and manage applications through containerization. Containers isolate applications and all their dependencies, making them easily portable and responsive.

Why do you need Docker?

It simplifies the process of developing, testing and deploying applications by ensuring compatibility between different environments. This is especially useful for teams working on complex projects, where you need to ensure that the application works the same on both the developer's local machine and on a server in the cloud.

Docker allows you to create images - templates based on which containers run. The images can contain all necessary libraries and customizations, which eliminates compatibility issues. Docker can also be used to quickly scale and manage applications, making it an indispensable tool in the modern DevOps and CI/CD process.

Basic Docker components: images, containers and volumes

Docker is based on three fundamental components: images, containers, and volumes. Docker images serve as a model for containers, providing all the necessary instructions and files needed to run the application. Containers, on the other hand, are running instances of these images, isolated from each other and from the host system, allowing multiple applications to run simultaneously without conflicts. Volumes play an important role in managing data persistence for containers by allowing data to be stored independently of the container's lifecycle. However, as projects evolve, it is often necessary to clean up unused resources in Docker to free up space and keep the system running efficiently. This process typically involves removing unused images, stopped containers, and orphan volumes that can accumulate over time. By effectively managing these components, developers can provide a lean and optimized Docker environment, minimizing overhead and maximizing performance.

How do Docker images work?

Docker images are a critical component of the Docker ecosystem, serving as a blueprint for creating containers. Each image consists of a layered file system, where each layer represents a set of changes made to the image, such as adding files or installing software. This layered architecture allows for efficient storage and transfer of data because multiple images can share layers, reducing redundancy and saving disk space.

Installing and updating images

As you work with Docker, installing and updating images plays an important role in keeping your containers up to date. Images are the templates from which containers are created, and updating them is necessary to implement new features, fix bugs, and improve security. To install a new image, you can use the command:
docker pullYou need to specify the name of the image and its tag. For example, the following command will allow you to download the latest Ubuntu image:
docker pull ubuntu:latestWhen updating images, keep in mind that older versions can take up a significant amount of disk space. Keeping images up to date not only improves the performance of your applications, but also ensures their security.

Why do you need cleanup in Docker?

Cleanup in Docker plays an important role in maintaining the efficiency and performance of your container environment. When you work with Docker, over time unnecessary images, stopped containers, and temporary volumes accumulate and take up precious disk space. These accumulated resources can cause your system to slow down and make it difficult to manage containers. Removing old images and containers not only frees up space, but also simplifies the process of deploying new applications. In addition, cleaning helps avoid conflicts between different versions of images, which can be critical during development and testing.  Periodic cleanup in Docker also helps to better organize the workspace, allowing developers to focus on relevant projects and avoid tangling with outdated elements. Ultimately, regular cleanup is integral to the effective use of Docker and container infrastructure management.

Clearing all unused

To get rid of everything unused in Docker use the command:
docker system pruneTo remove all stopped containers and unused images, add the -a flag to this command:
docker system prune -a

Deleting Docker images

Deleting a specific image

To find the ID of the image you want to delete, use the command:
docker images -aThe command will display a list of images.
To delete the desired image or images, use the command:
docker rmi Name1 Name2

Deleting images that are not bound to a container

In the context of Docker cleanup, removing images that are not associated with any container is an important step. These unlabeled or “hanging” images can accumulate over time, taking up valuable disk space and causing potential confusion when managing available images. By identifying and removing these derelict images, you can streamline your Docker environment, making it more efficient and easier to navigate. Regularly cleaning up these unrelated images is a best practice for maintaining optimal Docker performance, especially in environments where images are frequently created and modified. By incorporating this cleanup operation into routine maintenance, users can ensure that their Docker environment remains organized and efficient.

A list of unlinked images can be obtained with the command:
docker images -f dangling=trueAnd you can delete it all together with a command:
docker images purge

Deleting images by regular expression

In cases when there are quite a lot of Docker images and it is difficult to list them one by one for deletion, you can use regular expressions. You can get a list of such images using different methods. One of them is:
docker images -a |  grep 'pattern'After verifying that the pattern is correct, you can delete all docker images with the following command:
docker images -a | grep 'pattern' | awk '{print $3}' | xargs docker rmi

Delete all Docker images

Deleting all docker images can be accomplished quite easily with a single command:
docker rmi $(docker images -a -q)

Deleting Docker containers

Deleting a specific container

To search for a container name or identifier, use the command:
docker ps -aAnd you can delete the required docker containers with the command:
docker rm ID1_or_Name1 ID2_or_Name2

Deleting a container at the end of use

Creating a container and then deleting it when you finish working in it, can be done with the command:
docker run --rm your_image_nameIn this case, it will be automatically deleted when you leave the container.

Deleting containers by status

To find containers with a specific status (created, restarting, running, paused or exited) use the -f flag to filter:
docker ps -a -f status=exitedYou can delete all docker containers filtered by status with the command:
docker rm $(docker ps -a -f status=exited -q)You can delete containers with multiple statuses as follows:
docker rm $(docker ps -a -f status=paused -f status=exited -q)

Deleting containers by regular expression

As with images, there is an option to remove containers using a regular expression search:
docker ps -a | grep 'pattern'After verifying that the pattern is correct, you can delete all docker containers with the following command:
docker ps -a | grep 'pattern' | awk '{print $3}' | xargs docker rmi

Stopping and deleting all containers

You can stop and delete all Docker containers without exception, but first of course you should make sure that they can actually be deleted. Check the list of containers:
docker ps -aIf everything is correct, you can stop and then delete all containers with the command:
docker stop $(docker ps -a -q)
docker rm $(docker ps -a -q)

Deleting Docker volumes

Deleting a specific volume

Use the command below to find the names of the docker volumes you want to delete:
docker volume lsAnd perform the removal itself as follows:
docker volume rm volume_name1 volume_name2

Deleting unlinked volumes

It is important to realize that when you delete a container, the volume will not be deleted along with it. This creates volumes that are not associated with any containers. These are called unbound Docker volumes.
You can display a list of such unbound volumes with the command:
docker volume ls -f dangling=trueAnd you can delete all unlinked volumes with a single command:
docker volume prune

Deleting a Docker container together with a volume

There is only one way to delete a volume together with its container - if the docker volume was created without a name. Use the -v flag for such deletion:
docker rm -v Container_NameNote the output of the command. If a container is successfully deleted, its identifier will be displayed. But if the volume has a name, it will remain in the system and there will be no notification about it.

Conclusion

The above are the most common tasks that users do to keep docker clean and manually delete images, containers and volumes. Of course, there is a long list of commands that are used to manage docker.