Question: I'm using [Docker for Mac](https://docs.docker.com/docker-for-mac/) Version 1.12.0-beta21 (build: 11019) on OS X 10.11.6. The container folder in `$HOME/Library/Containers/com.docker.docker` contains 3.1 GB of space. `docker images -a` however only shows one image which is 330 MB.

How can I clean up the container folder, so that it only contains the images I'm able to use?

Update
======

There is an open issue regarding this problem: <https://github.com/docker/for-mac/issues/371>

Answer: 
try:

```
docker system prune -a

```

<https://docs.docker.com/engine/reference/commandline/system_prune/>

> 
> Remove all unused containers, networks, images (both dangling and
>  unreferenced), and optionally, volumes.
> 
> 
>
Spotify have a useful docker image called [docker-gc](https://github.com/spotify/docker-gc) which will clean up unused images.

As per the Github page for it, you can run it as a container itself:

`docker run --rm -v /var/run/docker.sock:/var/run/docker.sock -v /etc:/etc spotify/docker-gc`

I have that aliased to `docker-gc` which I run periodically to clean things up.