crowdstf/docker/extras/docker-cleanup-dangling-images.service

[Unit]
Description=Clean up dangling Docker images
After=docker.service
Requires=docker.service

[Service]
Type=oneshot
ExecStart=/usr/bin/env sh -c '/usr/bin/docker images -q --filter "dangling=true" | xargs -t --no-run-if-empty /usr/bin/docker rmi'