README.md: Working toward basic documentation (#10)

* README.md: document config file

Still pretty sparse, but as this bit is necessary to actually use
pi-gen, here it is.

* README.md: Overview of Raspbian's stages

* README.md: Stages -> Raspbian Stages + heading

Decided that the Stages heading probably made more sense as being
retitled to refer specifically to Raspbian since it has no direct
bearing on pi-gen itself which could produce any Debianish system for
the pi, and also that there ought to be a Stage Anatomy section first
talking about the nuts and bolts of what goes into these stages.

Stage Anatomy is just a heading for now.

* README.md: Make Config section less conversational

Left the stage overview as it was since it's intended more as a plain
language explanation than a technically complete look.  I believe that
kind of information is useful to have, but perhaps as README.md becomes
longer it may be advisable to move it to another location.
pull/15/head
Joseph Carter 2016-09-04 21:02:39 -07:00 committed by XECDesign
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#Dependencies
`quilt kpartx realpath qemu-user-static debootstrap zerofree pxz`
#Config
Upon execution, `build.sh` will source the file `config` in the current
working directory. This bash shell fragment is intended to set needed
environment variables.
The following environment variables are supported:
* `IMG_NAME`, the name of the distribution to build (required)
* `APT_PROXY`, proxy/cache URL to be included in the build
A simple example for building Raspbian:
```bash
IMG_NAME='Raspbian'
```
#Stage Anatomy
#Raspbian Stage Overview
The build of Raspbian is divided up into several stages for logical clarity
and modularity. This causes some initial complexity, but it simplifies
maintenance and allows for more easy customization.
- Stage 0, bootstrap. The primary purpose of this stage is to create a
usable filesystem. This is accomplished largely through the use of
`debootstrap`, which creates a minimal filesystem suitable for use as a
base.tgz on Debian systems. This stage also configures apt settings and
installs `raspberrypi-bootloader` which is missed by debootstrap. The
minimal core is installed but not configured, and the system will not quite
boot yet.
- Stage 1, truly minimal system. This stage makes the system bootable by
installing system files like `/etc/fstab`, configures the bootloader, makes
the network operable, and installs packages like raspi-config. At this
stage the system should boot to a local console from which you have the
means to perform basic tasks needed to configure and install the system.
This is as minimal as a system can possibly get, and its arguably not
really usable yet in a traditional sense yet. Still, if you want minimal,
this is minimal and the rest you could reasonably do yourself as sysadmin.
- State 2, lite system. This stage produces the Raspbian-Lite image. It
installs some optimized memory functions, sets timezone and charmap
defaults, installs fake-hwclock and ntp, wifi and bluetooth support,
dphys-swapfile, and other basics for managing the hardware. It also
creates necessary groups and gives the pi user access to sudo and the
standard console hardware permission groups.
There are a few tools that may not make a whole lot of sense here for
development purposes on a minimal system such as basic python and lua
packages as well as the `build-essential` package. They are lumped right
in with more essential packages presently, though they need not be with
pi-gen. These are understandable for Raspbian's target audience, but if
you were looking for something between truly minimal and Raspbian-lite,
here's where you start trimming.
- Stage 3, desktop system. Here's where you get the full desktop system
with X11 and LXDE, web browsers, git for development, Raspbian custom UI
enhancements, etc. This is a base desktop system, with some development
tools installed.
- Stage 4, complete Raspbian system. More development tools, large packages
like LibreOffice, email, sonic-pi, wolfram-engine, etc. All the things.