不要なイメージが溜まってきたので以下のコマンドを実行したら6ギガぐらい空いた
# docker system prune
WARNING! This will remove:
- all stopped containers
- all volumes not used by at least one container
- all networks not used by at least one container
- all dangling images
Are you sure you want to continue? [y/N] y
Total reclaimed space: 6.619 GB