title: What are the values listed under "Layers" in Docker Image Inspect?
body: <p>I am trying to write a program that ensure that the parent (or grandparent or great grandparent, etc) of a container is a container on a an approved list of containers.  (To ensure that only approved containers are used in my company.)</p>
  <p>When I run the command <code>docker image inspect</code> on my image I get some json in response.  Part of that json looks like this:</p>
  <pre>
  "RootFS": {
      "Type": "layers",
      "Layers": [
          "sha256:cb42413394c4059335228c137fe884ff3ab8946a014014309676c25e3ac86864",
          "sha256:800afb4d883be4a1552b6afb33602caf7c69d5d9caa929aa961e74dd4df1f7fa",
          "sha256:6db0849b3e99f6471e878c20fdc1449623a5374d563f8463a791533f80f0387b",
          "sha256:f3bc884425c59baed7a7487a156c18d091ee1b567ab2bb9d286f110d31abb020",
          "sha256:139aa1a59c8a79c06c61077a51f83793e977bc818875d70ad1cfe7ce9e96cecd",
          "sha256:093496e1b286284fe6158c87e50aff6a905b809ee5f76d9c1897945fc53fd84c",
          "sha256:86248bc7c05ebaee4860efed18d1f6225909bbc03eccedd36ea4a154275540e1",
          "sha256:fe5e09df9bed600922ead78527eb7ff8a6b241dcee185aaa1213942b484cb769",
          "sha256:8b9bd48d3c62d7ddac27dfcc2c3c0cded5ef8ee530118b9212c8f4b8fd2e6faf",
          "sha256:4466146b6e2c6e31ffc6bf194ad75758e641e4f99dc6020b67d37024d9f99a98",
          "sha256:68f8345afd825ee2a0b675b5e93eb7b5504ad71a77136ba2014bd876e3ddbe68",
          "sha256:49a130b8b29dc6ac46c23bee6ffea315fe4b8ce4f621926834ad5e4fe7694a00",
          "sha256:bd13a0d30d036bbbd17d539310d0f821405c882419db56884a9562aa6d538975",
          "sha256:68f4281d14f5e70fc4a558fd4e3affcef4185d3fde53cd758cf46070327bbb06",
          "sha256:4410271de2fbbc8c72d545dfe212c29b83dc9e94e53a101e92526bdfcc566070",
          "sha256:5df5ddaa2216e7fa23096d325a984ca5993b6b04100850202a51abdac543f324",
          "sha256:a938e714d49d5122040f6af3dffc68efb1e9f19167e0982d4e1d2f5932166bec",
          "sha256:6e835bd4ceec7cc3b858dbbb61c32f08e27d3171428c76806bfab53616be1bad"
      ]
  },
  </pre>
  <p>I thought these would be the layers of my container image.  But the list does not contain the container image's parent.  By parent, I mean the container image used in the <code>FROM</code> clause to create the image I inspected.)  (I checked using the <code>docker image ls --digests</code> command.)</p>
  <p>What are these values?</p>
  <p><strong>And more importantly, is there a way to get a list of the actual layers of a container?</strong></p>