Where are Docker images stored on the host machine?

The contents of the /var/lib/docker directory vary depending on the driver Docker is using for storage.

By default this will be aufs but can fall back to overlay, overlay2, btrfs, devicemapper or zfs depending on your kernel support. In most places this will be aufs but the RedHats went with devicemapper.

You can manually set the storage driver with the -s or --storage-driver= option to the Docker daemon.

• /var/lib/docker/{driver-name} will contain the driver specific storage for contents of the images.
• /var/lib/docker/graph/<id> now only contains metadata about the image, in the json and layersize files.

In the case of aufs:

• /var/lib/docker/aufs/diff/<id> has the file contents of the images.
• /var/lib/docker/repositories-aufs is a JSON file containing local image information. This can be viewed with the command docker images.

In the case of devicemapper:

• /var/lib/docker/devicemapper/devicemapper/data stores the images
• /var/lib/docker/devicemapper/devicemapper/metadata the metadata
• Note these files are thin provisioned "sparse" files so aren't as big as they seem.

When using Docker for Mac Application, it appears that the containers are stored within the VM located at:

~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2

UPDATE (Courtesy of mmorin):

As of Jan 15 2019 it seems there is only this file:

~/Library/Containers/com.docker.docker/Data/vms/0/Docker.raw

that contains the Docker Disk and all the images and containers within it.

Actually, Docker images are stored in two files as shown by following command

$ docker info

Data file: /var/lib/docker/devicemapper/devicemapper/data

Metadata file: /var/lib/docker/devicemapper/devicemapper/metadata