Docker allows one to build on a specific version of an operating
system without having that version installed on the host.  This
example was tested on Debian Bullseye, but the build was actually
done on the Ubuntu Bionic Docker image.

The following docker related packages were installed:

  ii  docker-ce                                     5:20.10.14~3-0~debian-bullseye   amd64        Docker: the open-source application container engine
  ii  docker-ce-cli                                 5:20.10.14~3-0~debian-bullseye   amd64        Docker CLI: the open-source application container engine
  ii  docker-ce-rootless-extras                     5:20.10.14~3-0~debian-bullseye   amd64        Rootless support for Docker.
  ii  docker-scan-plugin                            0.17.0~debian-bullseye           amd64        Docker scan cli plugin.

build-docker.sh was run from the command line to create the docker
container called mlinux-build.

The build starts sshd, but it is not needed if you use the docker
exec command to attach to the Docker image as is done in
build-mlinux.sh.

After the build is complete you should have a login shell.  You
could then do:

  su -l mlbuilder
  build-mlinux.sh

After the build completes, the output files can be copied to
the host as follows:

  docker cp mlinux-build:/home/mlbuilder/mlinux-6.0.0/build/tmp/deploy/images/mtcdt/mlinux-base-image-mtcdt-upgrade-withboot.bin .