"Funtoo From Scratch" contains automation technology for Funtoo's Evolved Bootstrap project, which can be found here:

https://www.funtoo.org/Funtoo:Evolved_Bootstrap

This technology can be used to bootstrap a Funtoo stage1 tarball, as well as "Alkaline" MUSL micro-containers, completely from sources, bootstrapping the system using a cross-compiler (which itself is bootstrapped using a local compiler) to ensure the resultant built binary environment is a completely new, "greenfield" environment built from source code, not inheriting any binary parts from any previously-built environment.

It leverages the fchroot tool to perform building of non-native arches, such as arm-64bit, on x86-64bit systems.

• gnu -- Funtoo Stage1 Tarball -- this is an initial Funtoo Linux system that can be used by metro to build a full Funtoo Linux system. Supported build system is x86-64bit, and supported targets are x86-64bit, arm-64bit (aarch64) and riscv-64bit.
• musl -- Alkaline MUSL Micro-Container -- this is a functioning MUSL-based environment that can be used as a starting point for building custom runtimes. Supported build system is x86-64bit, and supported targets are x86-64bit, arm-64bit (aarch64) and riscv-64bit. Work is ongoing on support for powerpc-64bit.

It is possible to run Funtoo From Scratch in any Linux or any Linux-like environment that has a C compiler, with minimal dependencies. If you want to bootstrap on something that is missing common modern things like Python 3, it is indeed possible to adapt things to do this.

However, most people will prefer having the ability to dynamically generate the build scripts on the build system directly based YAML and templates, and this requires Python 3, PyYAML and Jinja2 installed. The Python scripts will dynamically generate bash scripts from YAML which will perform the actual build process. Our YAML is designed to be clean, elegant and intuitive to use so it's what you want to edit if you are working on improving or augmenting the build steps.

To use Funtoo From Scratch to build for a non-native architecture, fchroot and its associated QEMU and QEMU-related dependencies must be installed, and a Linux system must be used.

The "ideal" setup for Funtoo From Scratch is on a Linux system with LXD installed, for which we have a developer-centric build system that will do the full FFS build within an isolated Funtoo container. This means that you don't actually need PyYAML, Jinja2, QEMU and Fchroot on your local system, as they will be automatically installed and used inside the container.

This allows for rapid and isolated development of Funtoo from Scratch, as well as launching multiple simultaneous builds, the use of incremental snapshots to allow re-launching the build from the last successful phase, and other handy features.

We recommend you start with the LXD environment under Funtoo if at all possible, and once comfortable in that environment, explore more minimal approaches to using Funtoo from Scratch if needed. We actively use the LXD setup so it is the official supported and maintained method at this time.

This section documents the "ideal" LXD-based setup which we recommend as a starting point.

First, you will want to set up LXD under Funtoo Linux as documented here:

https://www.funtoo.org/LXD

You will want to ensure that lxdbr0 is configured to provide network connectivity to your containers and that the default profile is sufficient to provide a single network interface on this network.

If these assumptions are not suitable for your environment, the following environment variables can be exported to customize the behavior of the ffs script:

• LXD_LAUNCH_EXTRA_ARGS which defaults to -p default -n lxdbr0.
• LXD_FFS_SOURCE_IMAGE which sets the LXD image to use for builds and defaults to funtoo-fchroot.
• LXD_INTERFACE which specifies the interface to configure inside the LXD container and defaults to eth0.

Next, import a suitable LXD tarball from https://build.funtoo.org and save it with the alias of funtoo-fchroot:

$ wget https://build.funtoo.org/next/x86-64bit/intel64-skylake/2022-07-21/lxd-intel64-skylake-next-2022-07-21.tar.xz
$ lxc image import lxd-intel64-skylake-next-2022-07-21.tar.xz --alias funtoo-fchroot

Fchroot does not need to be pre-installed in this image, but if you do customize it to pre-install Fchroot, then it will speed up repeated launches of builds as Fchroot and QEMU will not need to be emerged each time.

To launch a Funtoo from Scratch build, you will simply use our ffs script located under ci/lxd-baremetal/bin:

$ cd ~/ffs
$ ci/lxd-baremetal/bin/ffs gnu arm-64bit

This will instantiate a container named ffs-<username>-arm-64bit-gnu-test, and will perform the build inside the container at the path /root/ffs-repo. You will see output of the build as it runs on your console, but the actual build itself is happening within the container. To stop the build, press ^C. As various phases of the build are completed, snapshots will be taken. If you restart the build, you will be prompted as to whether you would like to use these snapshots as a starting point, or if you want to delete them instead. This is a handy feature if you are trying to fix a build issue that happens relatively late in the bootstrap.

It's also important to note that our magic ffs script uses special tricks to grab any local changes you have made within the ffs repository when launching a build. This allows you to develop locally on a Linux host, and the builds you fire off inside LXD will grab these changes automatically.

This should allow you to start playing with Funtoo from Scratch. While we have covered the basic first steps here, we have just introduced you to the first layer of Funtoo from Scratch. We also need to describe the YAML files in this repository that define what packages get built, and how they get built, so that you know how to customize builds as needed. This will be covered in the next sections, coming soon.