Why is the file deleted in docker but the disk is still 100%?

In the process of using Docker, many people may encounter the problem that after deleting the Docker image or container, the disk space occupied has not been reduced and is still 100%. Why is this? Let’s take a closer look.

1. Basic use of Docker

Before understanding the cause of the problem, let us briefly review the basic use of docker.

Run the docker container:

docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

where IMAGE is the name of the image to be run, which can be passed docker images Command view;

OPTIONS can include the following:

-d specifies the container to run in the background;

-p specifies the container port mapping, the format is: host port: Container port;

--name specifies the container name;

-v specifies the mount point of the host directory and container directory;

rm automatically deletes the container.

Delete docker container:

docker rm CONTAINER [CONTAINER...]

where CONTAINER refers to the name or ID of the container, which can be viewed through the docker ps -a command.

Delete docker image:

docker rmi IMAGE [IMAGE...]

IMAGE refers to the name or ID of the image, which can be viewed through the docker images command.

2. Problem Analysis

When using the above command to delete a Docker container or image, there are usually two situations:

1. Delete the container: When we use When the docker rm CONTAINER command deletes a container, Docker will automatically delete the file system used by the container, because each container "can" have its own independent file system. Therefore, when a container is deleted, the space it occupies will also be released.
2. Delete an image: When we use the docker rmi IMAGE command to delete an image, Docker will delete all historical versions of the image and the intermediate layers, while retaining all content required by the containers that are still using the image. Therefore, if an image has been used by multiple containers, deleting the image will not release all the space occupied by the image.

Based on the above situation, we can draw a conclusion: deleting Docker containers or images does not guarantee the immediate release of disk space, and requires manual cleaning using specific tools.

3. Solution

Docker actually uses the file system of the host when running. Therefore, when the Docker container or image is deleted, we need to manually clean up the files left on the host. Only by removing junk files can the disk space be released.

The following is the specific cleaning method:

1. Clean up the junk files generated by the container

In the Docker container, some temporary files or log files may will be retained, so when deleting the container, you need to delete these files together to avoid taking up too much space.

Can be cleaned by the following command:

docker ps -aq | xargs docker rm -v

The function of this command is: find the IDs of all containers and put them Pass the ID to the docker rm command to let docker automatically delete the corresponding container and all associated volumes.

2. Clean up unused images

When we run the container, Docker will download the required image from the official repository or other custom repositories and store it locally Backup. Although these backups take up less space, they can also lead to insufficient disk space if there are a large number of unused images.

You can check unused images with the following command:

docker images -q | xargs docker inspect --format='{{.Id}} {{.RepoTags}} {{. Size}}' | sort -k 3 -h

The function of this command is to list the IDs, tags and sizes of all images and sort them by size.

You can use the following command to delete all idle images:

docker images -qf dangling=true | xargs docker rmi

The function of this command is: find all unused images mirror and delete them.

3. Clean the Docker data directory

Finally, if the above two methods are ineffective, you can manually clean the Docker data directory. By default, the Docker data directory is located under /var/lib/docker/.

You can use the following command to clean up the directory:

docker system prune -a -f

The function of this command is: delete all unused objects, including unused images , unused data and unused build cache.

4. Summary

In the process of using Docker, in order to free up disk space, we need to manually clean up some junk files left in the containers, images, and Docker data directories. These files not only occupy a lot of disk space, but also occupy system resources and affect system performance. Therefore, it is very necessary to clean Docker junk files regularly.

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