2. Issue the following command to retag the Ubuntu image: 3. Use the  docker images  command to confirm that a tag was added to the Ubuntu image. Example 6-3 Listing Available Docker Images admin@fcc1a71d8f61 :~$ docker images REPOSITORY TAG IMAGE ID CREATED SIZE myregistry latest 082be17251ee 30 hours ago 441MB ibm_zcx_zos_cli_image latest 00f61e376fd0 3 days ago 363MB ubuntu 16.04 f8835575bd80 3 weeks ago 64.8MB ubuntu latest f8835575bd80 3 weeks ago 64.8MB s390x/ubuntu 16.04 fcae39a6d474 6 weeks ago 118MB 4. Now, remove the tag for  ubuntu:latest  by running the following command: You should receive a message ” Untagged: ubuntu:latest ”. For more details in how to work with tags, see Section 6.7, “Working with tags” on page 136  in this publication. 6.3 Building a private registry image There is a registry image available in Docker Hub for IBM Z platform. The name of this image  is  ibmcom/registry-s390x  and its available in Docker Hub. For more details, see  https://hub.docker.com/r/ibmcom/registry-s390x . For our private registry deployment, we use  ibmcom/registry-s390x , and the building of an  image is not required. However, this section provides good concepts and commands that  might be helpful for application developers who manage Docker instances. This procedure  can also be used if you do not find a registry image with the version that you want to install. The following steps work only when the zCX instance has internet access. The image build  process downloads and installs some components into the new image when it executes the  instructions of the Dockerfile. You see more details in Example 6-8, which shows the output of  the build process. Use the procedure in this section to build a private registry image. Again, we recommend that  you use the available registry image for  s390x  ( ibmcom/registry-s390x ). If your zCX instance  is behind a firewall, go to the following section. 1. Connect via SSH into your zCX instance by using the command in Example 6-4. Be sure  to replace the IP address with one that is valid for your zCX environment. Example 6-4 Connecting to zCX instance erics-mbp:.ssh ibmuser$  ssh admin@129.40.23.70 -p 8022 Warning: Permanently added '[129.40.23.70]:8022' (ECDSA) to the list of known hosts. Welcome to the IBM z/OS Container Extensions (IBM zCX) shell that provides access to Docker commands. For more information on how to use this shell to execute Docker commands refer to "IBM z/OS Container  Extensions Guide". Last login: Fri Sep 6 15:22:36 2019 from 9.57.181.31 114  Getting started with z/OS Container Extensions docker tag ubuntu:latest ubuntu:16.04 d ocker rmi ubuntu:latest