Create an Ubuntu 20.04 Docker image using debootstrap

To create an Ubuntu 20.04 Docker image using debootstrap, follow these steps:

Prerequisites

Make sure you have the following installed:

debootstrap
chroot
tar
docker

You can install debootstrap on your system if it’s not already there:

sudo apt update
sudo apt install debootstrap

1. Create the Ubuntu 20.04 Root Filesystem with `debootstrap`

Use debootstrap to create a minimal Ubuntu 20.04 filesystem in a local directory (e.g., ubuntu-20.04):

sudo debootstrap --arch=amd64 focal ubuntu-20.04 http://archive.ubuntu.com/ubuntu/

This command downloads and installs a basic Ubuntu 20.04 environment into the ubuntu-20.04 directory. The --arch=amd64 option specifies the architecture, and focal is the codename for Ubuntu 20.04.

2. Configure the Filesystem (Optional)

You can perform additional configuration within the new root filesystem. For example, set up a basic sources.list for apt or install some packages.

To enter the chroot environment:

sudo chroot ubuntu-20.04

Inside chroot, you can set up a sources.list file or install any necessary packages. For example, to update the package list:

apt update

Once you’re done, exit the chroot environment:

exit

3. Package the Filesystem as a TAR Archive

Next, create a tarball from the ubuntu-20.04 directory:

sudo tar -C ubuntu-20.04 -c . | sudo docker import - ubuntu:20.04

This command:

Uses tar to archive the contents of the ubuntu-20.04 directory.
Pipes the archive to Docker’s import command.
Tags the imported image as ubuntu:20.04.

4. Verify the Docker Image

You can verify that the image has been created by listing your Docker images:

docker images

You should see ubuntu with the tag 20.04 in the list.

5. Run a Container from the Image

To test the new image, run a container:

docker run -it ubuntu:20.04 /bin/bash

You should now be inside a running container based on your custom Ubuntu 20.04 image created with debootstrap.