Application Image Builder
=========================

Application Images (or appimgs for short) are created with this builder
framework. The build is controlled by a configuration file and this
configuration file is actually a shell script that follows the conventions
described in the Configuration File section of this document.

Stage One
---------

The Stage One builder uses debootstrap to build a very minimal debian
installation.  Then a chroot is set up and stage-two.sh is executed inside the
chroot to perform most of the installation.

Stage Two
---------

The stage-two.sh script mostly just orchestrates the execution of small
fragments of shell script code that are called 'modules'.  The base framework
modules can be found in the directory /usr/share/appimg-builder/appimg-modules.

It imports the configuration file with the 'source' command after all the key
variables and functions have been defined.  It's possible to override any of
these variables and functions simply by defining another version with the same
name in the configuration file, but you should almost never need to do this.

Configuration File
------------------

- Variables

PACKAGES can be set to a list of additional packages to add to the base set of
packages.

  PACKAGES="extremetuxracer biff anarchism" 

PRE_INSTALL_MODULES can be set to a list of modules to run before the main
package installation stage happens.  The contents will be appended to a
pre-defined list of 'base' modules that run.

  PRE_INSTALL_MODULES="my-cool-module another-module"

If complete control over the modules to run is required, you can override the
variable BASE_PRE_INSTALL_MODULES entirely rather than providing
PRE_INSTALL_MODULES.  Other modules depend on 'utility-library' so it is usually
required and should be the first module listed.

  BASE_PRE_INSTALL_MODULES="utility-library configure-locale custom-create-user"

POST_INSTALL_MODULES is a list of modules to execute after packages have been
installed.  It works exactly the same way as PRE_INSTALL_MODULES and also has a
corresponding 'base' variable that could be overidden if necessary.

- Modules

Modules can be functions that you define or they can be loaded from files on
disk. To use files rather than functions a directory named 'appimg-modules'
must exist as a subdirectory of the directory containing the configuration file.
Any files you place in this directory will be found by name during the module
execution stages.

- Installing Files

If you would like to have external files such as configuration files copied into
the image, create 'appimg-files' as a subdirectory of the directory containing
the configuration file.  You can then use the install_file command inside of a
module to copy the files from this directory. You can either store the files to
install in a flat directory or organize them into subdirectories mirroring the
location in which they will be installed.  Depending on which option you use,
the install_file command how two different modes.  In the examples below BASE
refers to the directory in which your configuration file is located.

   (1): install_file [mode] [file] [target directory]
  
   Example: Install BASE/appimg-files/my_config.conf 
              to /etc/mydaemon/my_config.conf 
  
        install_file 0644 my_config.conf /etc/mydaemon
     
   (2): install_file [mode] [full path] 
  
   Example: Install BASE/appimg-files/etc/mydaemon/my_config.conf 
              to /etc/mydaemon/my_config.conf
  
        install_file 0644 /etc/mydaemon/my_config.conf