1.2. How to Build a CLFS System

#### Cross-Compiled Linux From Scratch - Version 1.0.0rc1-PowerPC

### Chapter 1. Introduction

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# 1.2. How to Build a CLFS System

The CLFS system will be built by using a previously installed Linux distribution (such as Debian, Mandrake, Red Hat, or SuSE). This existing Linux system (the host) will be used as a starting point to provide necessary programs, including a compiler, linker, and shell, to build the new system. Select the “development” option during the distribution installation to be able to access these tools.

As an alternative to installing an entire separate distribution onto your machine, you may wish to use the Linux From Scratch LiveCD. The CD works well as a host system, providing all the tools you need to successfully follow the instructions in this book. Additionally, it contains all the source packages, patches and a copy of this book. So once you have the CD, no network connection or additional downloads are necessary. For more information about the LFS LiveCD or to download a copy, visit http://www.linuxfromscratch.org/livecd/

THE TEXT BELOW NEEDS TO BE REWRITTEN

Preparing a New Partition of this book describes how to create a new Linux native partition and file system, the place where the new CLFS system will be compiled and installed. Packages and Patches explains which packages and patches need to be downloaded to build a CLFS system and how to store them on the new file system. Final Preparations discusses the setup for an appropriate working environment. Please read Final Preparations carefully as it explains several important issues the developer should be aware of before beginning to work through Constructing Cross-Compile Tools and beyond.

Constructing Cross-Compile Tools explains the installation of cross-compile tools which will be built on the host but be able to compile programs that run on the target machine. These cross-compile tools will be used to create a temporary, minimal system that will be the basis for building the final CLFS system. Some of these packages are needed to resolve circular dependencies—for example, to compile a compiler, you need a compiler.

The process of building cross-compile tools first involves installing binutils into /cross-tools, so that the linker can be used with the building of everything else in the temp-system. GCC is then compiled statically and installed into /cross-tools, and this cross-compiler is used to build glibc into /tools for the temp-system. The GCC cross-compiler is then rebuilt dynamically - this final cross-compiler is what will be used to build the rest of the temporary system. When this is done, the CLFS installation process will no longer depend on the host distribution, with the exception of the running kernel.

The packages in Constructing a Temporary System are then built using the cross-compiled tools in /cross-tools, and linked against the C library that was installed during the building of the cross-tools.

This effort to isolate the new system from the host distribution may seem excessive, but a full technical explanation is provided at the beginning of Constructing a Temporary System.

In Installing Basic System Software, the full CLFS system is built. Depending on the system you are cross-compiling for, either you will boot the minimal temp-system on the target machine, or chroot into it.

The chroot (change root) program is used to enter a virtual environment and start a new shell whose root directory will be set to the CLFS partition. This is very similar to rebooting and instructing the kernel to mount the CLFS partition as the root partition. The major advantage is that “chrooting” allows the builder to continue using the host while CLFS is being built. While waiting for package compilation to complete, a user can switch to a different virtual console (VC) or X desktop and continue using the computer as normal.

Some systems cannot be built by chrooting so they must be booted instead. Generally, if you building for a different arch than the host system, you must reboot because the kernel will likely not support the target machine. Booting involves installing a few additional packages that are needed for bootup, installing bootscripts, and building a miminal kernel.

To finish the installation, the CLFS-Bootscripts are set up in Setting Up System Bootscripts, and the kernel and boot loader are set up in Making the CLFS System Bootable. The End contains information on furthering the CLFS experience beyond this book. After the steps in this book have been implemented, the computer will be ready to reboot into the new CLFS system.

This is the process in a nutshell. Detailed information on each step is discussed in the following chapters and package descriptions. Items that may seem complicated will be clarified, and everything will fall into place as the reader embarks on the CLFS adventure.

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