How to Reclaim Disk Space Used by Docker: A Complete Guide

Docker consumes a lot of disk space; running containers, pulling images, deploying applications, and building your own images can quickly fill up your storage.

You can view Docker’s disk usage with the command: $ docker system df The output categorises usage into four types:

Images : space taken by all images, both pulled and locally built.

Containers : space used by the writable layer of each running container.

Local Volumes : space occupied by data volumes mounted by containers.

Build Cache : cache generated during image builds (available with BuildKit in Docker 18.09+).

The RECLAIMABLE column shows how much space can be freed.

Container Disk Usage

When a container is created, Docker creates directories such as /var/lib/docker/containers/ID (logs) and /var/lib/docker/overlay2 (the writable layer).

Starting from a clean system, run an NGINX container and check disk usage: $ docker system df You will see one image (≈126 MB) and one container.

Create a 100 MB empty file inside the container:

$ docker exec -ti www \
  dd if=/dev/zero of=test.img bs=1024 count=0 seek=$[1024*100]

Running docker system df again shows the container’s space has increased; the file resides in the container’s writable layer.

Stopping the container makes that space reclaimable. You can delete stopped containers with: $ docker container prune Or remove all containers (running or stopped) with:

$ docker rm -f $(docker ps -aq)

$ docker container rm -f $(docker container ls -aq)

Image Disk Usage

Some images are “dangling” (no longer referenced) and can be removed. List dangling images: $ docker image ls -f dangling=true Delete them with:

$ docker image rm $(docker image ls -f dangling=true -q)

Or prune all unused images: $ docker image prune To delete every image (except those in use by containers):

$ docker image rm $(docker image ls -q)

Volume Disk Usage

Data volumes store persistent data outside the container’s filesystem. After testing a MongoDB container, the volume remains even after the container is removed.

Remove unused volumes with: $ docker volume rm $(docker volume ls -q) Or prune them:

$ docker volume prune

Build Cache Disk Usage

Docker 18.09 introduced BuildKit, which improves build performance and storage management. Clear the build cache with:

$ docker builder prune

One‑Click Cleanup

All the above resources share the prune sub‑command. Docker also provides a system‑wide prune to clean up any unused space: $ docker system prune Running this command regularly is a good habit to keep your machine tidy.