Suppose I have located a new (Linux like) Operating System for which there does not exist an image yet on some Docker hub (so for example: FROM theos:latest won’t help). How can you create a base image for the first time, for example when you got the iso of it ?
If you can get a tarball of the / of what you want your new image to be, you can import it with the docker import command. Each distro will have a different method to get that / layout in tarball format. Debian variants can be done relatively easily since they have the debootstrap tool.
There is an example for creating an ubuntu base image from scratch using the debootstrap tool in the docs: http://docs.docker.com/engine/articles/baseimages/
Other distros will have some other method available to bootstrap the root filesystem on a new installation.
Hopefully this helps.
/Jeff
Thanks. Somewhat googling serves me http://blog.allanglesit.com/2012/03/preparing-minimal-images-with-debootstrap/ . Hope I can find something for non-Debian families as well.