Merge pull request RPi-Distro#43 from sam3d/dev

Add stage specification documentation

README.md

@@ -1,12 +1,14 @@
-#TODO
+# pi-gen
+_Tool used to create the raspberrypi.org Raspbian images_
 
+### TODO
 1. Documentation
 
-#Dependencies
+## Dependencies
 
 `quilt kpartx realpath qemu-user-static debootstrap zerofree pxz zip dosfstools bsdtar libcap2-bin`
 
-#Config
+## Config
 
 Upon execution, `build.sh` will source the file `config` in the current
 working directory.  This bash shell fragment is intended to set needed
@@ -33,25 +35,25 @@ A simple example for building Raspbian:
 IMG_NAME='Raspbian'
 ```
 
-#Stage Anatomy
+## Stage Anatomy
 
 
 
-#Raspbian Stage Overview
+### 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
+ - **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
+ - **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
@@ -60,7 +62,7 @@ maintenance and allows for more easy customization.
    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
+ - **Stage 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
@@ -75,13 +77,24 @@ maintenance and allows for more easy customization.
    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
+ - **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, an email
+ - **Stage 4** - complete Raspbian system.  More development tools, an email
    client, learning tools like Scratch, specialized packages like sonic-pi and
    wolfram-engine, system documentation, office productivity, etc.  This is
    the stage that installs all of the things that make Raspbian friendly to
    new users.
+
+### Stage specification
+If you wish to build up to a specified stage (such as building up to stage 2 for a lite system), place an empty file named `SKIP` in each of the `./stage` directories you wish not to include.
+
+Then remove the `EXPORT*` files from `./stage4` (if building up to stage 2) or from `./stage2` (if building a minimal system).
+
+```
+# Example for building a lite system
+$ touch ./stage3/SKIP ./stage4/SKIP
+$ rm stage4/EXPORT*
+```