Docker history
Each Docker image is built by layers upon layers.
The docker history command can show you these layers.
docker history IMAGE
Here you can see that the Ubuntu image we have downloaded from the Docker Hub has 5 layers.
$ docker history ubuntu:20.04
IMAGE CREATED CREATED BY SIZE 74435f89ab78 4 weeks ago /bin/sh -c #(nop) CMD ["/bin/bash"] 0B <missing> 4 weeks ago /bin/sh -c mkdir -p /run/systemd && echo 'do… 7B <missing> 4 weeks ago /bin/sh -c set -xe && echo '#!/bin/sh' > /… 811B <missing> 4 weeks ago /bin/sh -c [ -z "$(apt-get indextargets)" ] 1.01MB <missing> 4 weeks ago /bin/sh -c #(nop) ADD file:b2342c7e6665d5ff3… 72.8MB