Ubuntu base image generator

Run sudo sh buildubu.sh to generate a Ubuntu base image.
It will use debootstrap, create a tar-file, generate the Dockerfile
and add a SHA256 checksum of the created tar-file to a ENV in the Dockerfile.
buildubu.sh will also add .git and any previously generated tar-files
to .dockerignore.

The generated Ubuntu wily image will weigh in around 105M compared to the Docker hub library
version which is around 133M.

Build and verify

sudo sh buildubu.sh <release> <mirror>

For example:

$ sudo sh buildubu.sh trusty http://se.archive.ubuntu.com/ubuntu/
$ docker build -t ubuntu -f Dockerfile .
$ docker run -t -i ubuntu bash

Recommended reading

Before you initiate a “docker pull”
Docker Security Cheat Sheet
Security Vulnerabilities in Docker Hub Images
what does docker.io run -it debian sh run?