Docker : build Ubuntu from Dockerfile

# ls -l
total 64240
-rw-r----- 1 root root     1383 Jan  8 13:39 Dockerfile
-rw-r----- 1 root root 65776957 Jan  8 13:40 ubuntu-trusty-core-cloudimg-amd64-root.tar.gz

These 2 files are downloaded from https://hub.docker.com/_/ubuntu/ (14.04)

# cat Dockerfile
FROM scratch
ADD ubuntu-trusty-core-cloudimg-amd64-root.tar.gz /

# a few minor docker-specific tweaks
# see https://github.com/docker/docker/blob/master/contrib/mkimage/debootstrap
RUN echo '#!/bin/sh' > /usr/sbin/policy-rc.d \
        && echo 'exit 101' >> /usr/sbin/policy-rc.d \
        && chmod +x /usr/sbin/policy-rc.d \
        \
        && dpkg-divert --local --rename --add /sbin/initctl \
        && cp -a /usr/sbin/policy-rc.d /sbin/initctl \
        && sed -i 's/^exit.*/exit 0/' /sbin/initctl \
        \
        && echo 'force-unsafe-io' > /etc/dpkg/dpkg.cfg.d/docker-apt-speedup \
        \
        && echo 'DPkg::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };' > /etc/apt/apt.conf.d/docker-clean \
        && echo 'APT::Update::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };' >> /etc/apt/apt.conf.d/docker-clean \
        && echo 'Dir::Cache::pkgcache ""; Dir::Cache::srcpkgcache "";' >> /etc/apt/apt.conf.d/docker-clean \
        \
        && echo 'Acquire::Languages "none";' > /etc/apt/apt.conf.d/docker-no-languages \
        \
        && echo 'Acquire::GzipIndexes "true"; Acquire::CompressionTypes::Order:: "gz";' > /etc/apt/apt.conf.d/docker-gzip-indexes

# enable the universe
RUN sed -i 's/^#\s*\(deb.*universe\)$/\1/g' /etc/apt/sources.list

# overwrite this with 'CMD []' in a dependent Dockerfile
CMD ["/bin/bash"]

---------------------------------
Now build ubuntu from Dockerfile

# docker build /tmp/ubuntu
Sending build context to Docker daemon 65.78 MB
Sending build context to Docker daemon
Step 0 : FROM scratch
 --->
Step 1 : ADD ubuntu-trusty-core-cloudimg-amd64-root.tar.gz /
 ---> 722fff301cf8
Removing intermediate container 3ac8f98d2503
Step 2 : RUN echo '#!/bin/sh' > /usr/sbin/policy-rc.d   && echo 'exit 101' >> /usr/sbin/policy-rc.d     && chmod +x /usr/sbin/policy-rc.d               && dpkg-divert --local --rename --add /sbin/initctl     && cp -a /usr/sbin/policy-rc.d /sbin/initctl    && sed -i 's/^exit.*/exit 0/' /sbin/initctl             && echo 'force-unsafe-io' > /etc/dpkg/dpkg.cfg.d/docker-apt-speedup             && echo 'DPkg::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };' > /etc/apt/apt.conf.d/docker-clean   && echo 'APT::Update::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };' >> /etc/apt/apt.conf.d/docker-clean   && echo 'Dir::Cache::pkgcache ""; Dir::Cache::srcpkgcache "";' >> /etc/apt/apt.conf.d/docker-clean              && echo 'Acquire::Languages "none";' > /etc/apt/apt.conf.d/docker-no-languages          && echo 'Acquire::GzipIndexes "true"; Acquire::CompressionTypes::Order:: "gz";' > /etc/apt/apt.conf.d/docker-gzip-indexes
 ---> Running in ca06d044f4ea
Adding 'local diversion of /sbin/initctl to /sbin/initctl.distrib'
 ---> c1007a188518
Removing intermediate container ca06d044f4ea
Step 3 : RUN sed -i 's/^#\s*\(deb.*universe\)$/\1/g' /etc/apt/sources.list
 ---> Running in 86a418b9a27f
 ---> e369918520d5
Removing intermediate container 86a418b9a27f
Step 4 : CMD /bin/bash
 ---> Running in b4e86758488e
 ---> 9d4dfcbd71bf
Removing intermediate container b4e86758488e
Successfully built 9d4dfcbd71bf

# docker images
REPOSITORY                              TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
<none>                                  <none>              9d4dfcbd71bf        5 minutes ago       187.9 MB
Fedora-Docker-Base-23-20151030.x86_64   latest              79c267013159        10 weeks ago        204.3 MB

# docker tag 9d4dfcbd71bf ubuntu:14.04
# docker images
REPOSITORY                              TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
ubuntu                                  14.04               9d4dfcbd71bf        6 minutes ago       187.9 MB
Fedora-Docker-Base-23-20151030.x86_64   latest              79c267013159        10 weeks ago        204.3 MB
# docker tag 79c267013159 fedora:latest
# docker images
REPOSITORY                              TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
ubuntu                                  14.04               9d4dfcbd71bf        8 minutes ago       187.9 MB
Fedora-Docker-Base-23-20151030.x86_64   latest              79c267013159        10 weeks ago        204.3 MB
fedora                                  latest              79c267013159        10 weeks ago        204.3 MB
# docker rmi Fedora-Docker-Base-23-20151030.x86_64
Untagged: Fedora-Docker-Base-23-20151030.x86_64:latest
# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
ubuntu              14.04               9d4dfcbd71bf        9 minutes ago       187.9 MB
fedora              latest              79c267013159        10 weeks ago        204.3 MB

Architecting Containers

http://rhelblog.redhat.com/2015/07/29/architecting-containers-part-1-user-space-vs-kernel-space/

http://rhelblog.redhat.com/2015/09/17/architecting-containers-part-2-why-the-user-space-matters-2/