Where can I find the sha256 code of a docker image?

Question

I'd like to pull the images of CentOS, Tomcat, ... using their sha256 code, like in

docker pull myimage@sha256:0ecb2ad60

But I can't find the sha256-code to use anywhere.

I checked the DockerHub repository for any hint of the sha256-code, but couldn't find any. I downloaded the images by their tag

docker pull tomcat:7-jre8

and checked the image with docker inspect to see if there's a sha256 code in the metadata, but there is none (adding the sha256 code of the image would probably change the sha256 code).

Do I have to compute the sha256 code of an image myself and use that?

Answer 1

Latest answer

Edit suggested by OhJeez in the comments.

docker inspect --format='{{index .RepoDigests 0}}' $IMAGE

Original answer

I believe you can also get this using

docker inspect --format='{{.RepoDigests}}' $IMAGE

Works only in Docker 1.9 and if the image was originally pulled by the digest. Details are on the docker issue tracker.

Answer 2

You can get it by docker images --digests

REPOSITORY          TAG    DIGEST                                                                    IMAGE ID     CREATED        SIZE
docker/ucp-agent    2.1.0  sha256:a428de44a9059f31a59237a5881c2d2cffa93757d99026156e4ea544577ab7f3   583407a61900 3 weeks ago    22.3 MB