1.2. How to Build a CLFS System

#### Cross-Compiled Linux From Scratch - Version 1.0.0rc2-MIPS64-Multilib

### 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, Fedora, Mandriva, SuSE, or Ubuntu). 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. This CD works well as a host system, providing all the tools you need to successfully follow the instructions in this book. It does also contain source packages and patches for the LFS book, and a copy of the LFS book, but not the needed packages or book for CLFS. You can still use the CD for building CLFS, but you will need to download the packages, patches and book separately. You can also look at http://www.linuxfromscratch.org/hints/downloads/files/lfscd-remastering-howto.txt for infomation on building your own CD, replacing the LFS packages and book with those for CLFS. 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/.

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 building and installing all the necessary tools to create a build system for the target machine. With these cross-compiled tools, we eliminate any dependencies on the toolchain from our host distro.

After we build our “Cross-Tools”, we start building a very minimal working system in /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, you will either 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. We also describe some alternative booting methods in Section 7.22, “What to do next”

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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