images: add Ubuntu 20.04 image

images/ubuntu/20.04/Containerfile

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+FROM docker.io/library/ubuntu:20.04
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+ENV NAME=ubuntu-toolbox VERSION=20.04
+LABEL com.github.containers.toolbox="true" \
+      com.redhat.component="$NAME" \
+      name="$NAME" \
+      version="$VERSION" \
+      usage="This image is meant to be used with the toolbox command" \
+      summary="Base image for creating Ubuntu toolbox containers" \
+      maintainer="Francesco Nicoletta Puzzillo <francesconicoletta@nomnp.com>"
+
+COPY README.md /
+
+RUN apt-get update
+
+COPY missing-docs /
+RUN apt-get -y reinstall $(cat missing-docs)
+RUN rm /missing-docs
+
+COPY extra-packages /
+RUN apt-get -y install $(cat extra-packages)
+RUN rm /extra-packages
+
+RUN apt-get clean
+
+COPY exempt_group /etc/sudoers.d/
+
+CMD /bin/sh

images/ubuntu/20.04/README.md

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+<img src="data/logo/toolbox-logo-landscape.svg" alt="Toolbox logo landscape" width="800"/>
+
+[![Zuul](https://zuul-ci.org/gated.svg)](https://softwarefactory-project.io/zuul/t/local/builds?project=containers/toolbox)
+[![Daily Pipeline](https://softwarefactory-project.io/zuul/api/tenant/local/badge?project=containers/toolbox&pipeline=periodic)](https://softwarefactory-project.io/zuul/t/local/builds?project=containers%2Ftoolbox&pipeline=periodic)
+
+[![Arch Linux package](https://img.shields.io/archlinux/v/community/x86_64/toolbox)](https://www.archlinux.org/packages/community/x86_64/toolbox/)
+[![Fedora package](https://img.shields.io/fedora/v/toolbox/rawhide)](https://src.fedoraproject.org/rpms/toolbox/)
+
+[Toolbox](https://github.com/containers/toolbox) is a tool for Linux operating
+systems, which allows the use of containerized command line environments. It is
+built on top of [Podman](https://podman.io/) and other standard container
+technologies from [OCI](https://opencontainers.org/).
+
+This is particularly useful on
+[OSTree](https://ostree.readthedocs.io/en/latest/) based operating systems like
+[Fedora CoreOS](https://coreos.fedoraproject.org/) and
+[Silverblue](https://silverblue.fedoraproject.org/). The intention of these
+systems is to discourage installation of software on the host, and instead
+install software as (or in) containers — they mostly don't even have package
+managers like DNF or YUM. This makes it difficult to set up a development
+environment or install tools for debugging in the usual way.
+
+Toolbox solves this problem by providing a fully mutable container within
+which one can install their favourite development and debugging tools, editors
+and SDKs. For example, it's possible to do `yum install ansible` without
+affecting the base operating system.
+
+However, this tool doesn't *require* using an OSTree based system. It works
+equally well on Fedora Workstation and Server, and that's a useful way to
+incrementally adopt containerization.
+
+The toolbox environment is based on an [OCI](https://www.opencontainers.org/)
+image. On Fedora this is the `fedora-toolbox` image. This image is used to
+create a toolbox container that seamlessly integrates with the rest of the
+operating system by providing access to the user's home directory, the Wayland
+and X11 sockets, networking (including Avahi), removable devices (like USB
+sticks), systemd journal, SSH agent, D-Bus, ulimits, /dev and the udev
+database, etc..
+
+
+## Installation
+
+Toolbox is installed by default on Fedora Silverblue. On other operating
+systems it's just a matter of installing the `toolbox` package.
+
+## Usage
+
+### Create your toolbox container:
+```console
+[user@hostname ~]$ toolbox create
+Created container: fedora-toolbox-33
+Enter with: toolbox enter
+[user@hostname ~]$
+```
+This will create a container called `fedora-toolbox-<version-id>`.
+
+### Enter the toolbox:
+```console
+[user@hostname ~]$ toolbox enter
+⬢[user@toolbox ~]$
+```
+
+### Remove a toolbox container:
+```console
+[user@hostname ~]$ toolbox rm fedora-toolbox-33
+[user@hostname ~]$
+```
+
+## Dependencies and Building
+
+Toolbox requires at least Podman 1.4.0 to work, and uses the Meson build
+system.
+
+The following dependencies are required to build it:
+- meson
+- go-md2man
+- systemd
+- go
+- ninja
+
+The following dependencies enable various optional features:
+- bash-completion
+
+It can be built and installed as any other typical Meson-based project:
+```console
+[user@hostname toolbox]$ meson -Dprofile_dir=/etc/profile.d builddir
+[user@hostname toolbox]$ ninja -C builddir
+[user@hostname toolbox]$ sudo ninja -C builddir install
+```
+
+Toolbox is written in Go. Consult the
+[src/go.mod](https://github.com/containers/toolbox/blob/main/src/go.mod) file
+for a full list of all the Go dependencies.
+
+By default, Toolbox uses Go modules and all the required Go packages are
+automatically downloaded as part of the build. There's no need to worry about
+the Go dependencies, unless the build environment doesn't have network access
+or any such peculiarities.
+
+## Distro support
+
+By default, Toolbox creates the container using an
+[OCI](https://www.opencontainers.org/) image called
+`<ID>-toolbox:<VERSION-ID>`, where `<ID>` and `<VERSION-ID>` are taken from the
+host's `/usr/lib/os-release`. For example, the default image on a Fedora 33
+host would be `fedora-toolbox:33`.
+
+This default can be overridden by the `--image` option in `toolbox create`,
+but operating system distributors should provide an adequately configured
+default image to ensure a smooth user experience.
+
+## Image requirements
+
+Toolbox customizes newly created containers in a certain way. This requires
+certain tools and paths to be present and have certain characteristics inside
+the OCI image.
+
+Tools:
+* `getent(1)`
+* `id(1)`
+* `ln(1)`
+* `mkdir(1)`: for hosts where `/home` is a symbolic link to `/var/home`
+* `passwd(1)`
+* `readlink(1)`
+* `rm(1)`
+* `rmdir(1)`: for hosts where `/home` is a symbolic link to `/var/home`
+* `sleep(1)`
+* `test(1)`
+* `touch(1)`
+* `unlink(1)`
+* `useradd(8)`
+* `usermod(8)`
+
+Paths:
+* `/etc/host.conf`: optional, if present not a bind mount
+* `/etc/hosts`: optional, if present not a bind mount
+* `/etc/krb5.conf.d`: directory, not a bind mount
+* `/etc/localtime`: optional, if present not a bind mount
+* `/etc/machine-id`: optional, not a bind mount
+* `/etc/resolv.conf`: optional, if present not a bind mount
+* `/etc/timezone`: optional, if present not a bind mount
+
+Toolbox enables `sudo(8)` access inside containers. The following is necessary
+for that to work:
+
+* The image should have `sudo(8)` enabled for users belonging to either the
+  `sudo` or `wheel` groups, and the group itself should exist. File an
+  [issue](https://github.com/containers/toolbox/issues/new) if you really need
+  support for a different group. However, it's preferable to keep this list as
+  short as possible.
+
+* The image should allow empty passwords for `sudo(8)`. This can be achieved
+  by either adding the `nullok` option to the `PAM(8)` configuration, or by
+  add the `NOPASSWD` tag to the `sudoers(5)` configuration.
+
+Since Toolbox only works with OCI images that fulfill certain requirements,
+it will refuse images that aren't tagged with
+`com.github.containers.toolbox="true"` and
+`com.github.debarshiray.toolbox="true"` labels. These labels are meant to be
+used by the maintainer of the image to indicate that they have read this
+document and tested that the image works with Toolbox. You can use the
+following snippet in a Dockerfile for this:
+```Dockerfile
+LABEL com.github.containers.toolbox="true"
+```
+The label `com.github.debarshiray.toolbox="true"` was used in previous versions
+of toolbox but is currently deprecated.

images/ubuntu/20.04/exempt_group

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+Defaults exempt_group=sudo

images/ubuntu/20.04/extra-packages

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+bash-completion
+bc
+bzip2
+diffutils
+findutils
+flatpak-xdg-utils
+git
+gnupg
+gnupg2
+hostname
+gvfs
+iputils-tracepath
+iputils-ping
+keyutils
+less
+libcap2-bin
+lsof
+man-db
+manpages
+mlocate
+mtr
+nano
+passwd
+pigz
+rsync
+sudo
+tcpdump
+time
+traceroute
+tree
+unzip
+wget
+zip
+xz-utils

images/ubuntu/20.04/missing-docs

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+acl
+apt
+bash
+curl
+gawk
+grep
+gzip
+libcap2
+openssl
+p11-kit
+python3
+sed
+systemd
+tar