参考文档：
https://docs.docker.com/engine/reference/commandline/system_prune/
命令：
docker system prune [OPTIONS]
参数：
--all , -a Remove all unused images not just dangling ones
--filter API 1.28+
Provide filter values (e.g. 'label==')
--force , -f Do not prompt for confirmation
--volumes Prune volumes
# 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加到crontab里自动执行：
docker clear disk
12 12 * * 0 docker system prune -f
手动清理：
# Remove exited containers
docker ps -a -q -f status=exited | xargs --no-run-if-empty docker rm -v
# Remove dangling images
docker images -f "dangling=true" -q | xargs --no-run-if-empty docker rmi
# Remove unused images
docker images | awk '/ago/ { print $3}' | xargs --no-run-if-empty docker rmi
# Remove dangling volumes
docker volume ls -qf dangling=true | xargs --no-run-if-empty docker volume rm