diskspace - Docker - free up space after removing all images & containers -

i have deleted images/containers

ubuntu@ubuntu:/var/lib/docker$ docker images repository          tag                 image id            created             size ubuntu@ubuntu:/var/lib/docker$ docker ps -a container id        image               command             created             status              ports               names 

but notice there still 15gb inside /var/lib/docker

ubuntu@ubuntu:/var/lib/docker$ sudo du --max-depth=1 -h . 12g     ./volumes 104k    ./aufs 4,0k    ./containers 1,3m    ./image 4,0k    ./trust 4,0k    ./swarm 2,6g    ./tmp 108k    ./network 15g     . 

questions:

1. how can free space?

2. is safe remove things inside /var/lib/docker?

try (from docker 1.13):

docker system df 

it shows size of:

• images
• containers
• local volumes

and remove local volumes using:

docker volume prune 

for older dockers try:

docker volume rm $(docker volume ls -q)