You need to understand Dockerimages and containers. Of course, this is understood from the perspective of the file system.

Docker images are read-only files. To emphasize, it is read-only, so we cannot actually delete the files in the image. When you delete it, you just make a mark so that the container cannot see the file. So this file still exists in the image and takes up disk space.

Docker container is a read-write layer based on the image, which is readable and writable. When reading and writing a file, the file is copied from the image to the read-write layer of the container, and then the copied file is read and written, while the original file is still in the image. Moreover, the read-write layer of this container also takes up disk space.

So, we can only free up disk space by deleting images and containers.

Delete image

sudo docker rmi <Image Name>

Delete container

sudo docker rm <Container Name>

Delete all images

sudo docker rmi -a

Delete all containers

sudo docker rm -a

In addition, the container’s data volume also takes up disk space. You can delete the expired volume through the following command:

sudo docker volume rm $(docker volume ls -qf dangling=true)

Of course, the most violent way is to delete the directory where Docker stores images, containers and data volumes (/var/lib/docker)

Use with caution! ! ! :

sudo service docker stop
sudo rm -rf /var/lib/docker
sudo service docker start