I am just slowly getting into Docker. I want to create an Ubuntu 16.04 image. I know that docker run -it ubuntu creates an ubuntu image but when I do that, I get 20.04
I wouldn't suggest making a 16.04 image since that was EOL as of April 2021. You can search the docker hub for "ubuntu 16.04" and find several instances of it
$ docker pull ubuntu:16.04 Trying to pull repository docker.io/library/ubuntu ... 16.04: Pulling from docker.io/library/ubuntu 58690f9b18fc: Pull complete b51569e7c507: Pull complete da8ef40b9eca: Pull complete fb15d46c38dc: Pull complete Digest: sha256:0f71fa8d4d2d4292c3c617fda2b36f6dabe5c8b6e34c3dc5b0d17d4e704bd39c Status: Downloaded newer image for docker.io/ubuntu:16.04
and then run it with:
$ docker run -it --rm ubuntu:16.04 /bin/bash root@b912d2c0db04:/# cat /etc/os-release NAME="Ubuntu" VERSION="16.04.7 LTS (Xenial Xerus)" ID=ubuntu ID_LIKE=debian PRETTY_NAME="Ubuntu 16.04.7 LTS" VERSION_ID="16.04" HOME_URL="http://www.ubuntu.com/" SUPPORT_URL="http://help.ubuntu.com/" BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/" VERSION_CODENAME=xenial UBUNTU_CODENAME=xenial
and you can use
FROM ubuntu:16.04 in your docker files to reference it.
16.04 after the colon in the name identifies which version you're pulling down, if you don't specify it, there's some convention that defaults to latest, which would be 20.04, until sometime in April 2022.