source: BOOK/introduction/common/how.xml @ bc610664

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<sect1 id="ch-intro-how">
  <?dbhtml filename="how.html"?>

  <title>How to Build a CLFS System</title>

  <para>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 <quote>development</quote> option
  during the distribution installation to be able to access these
  tools.</para>

  <para>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
  <ulink url="&hints-root;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 <ulink url="&livecd-root;"/>.</para>

  <para><xref linkend="chapter-partitioning"/> 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. <xref
  linkend="chapter-getting-materials"/> explains which packages and
  patches need to be downloaded to build a CLFS system and how to store
  them on the new file system. <xref linkend="chapter-final-preps"/>
  discusses the setup for an appropriate working environment. Please read
  <xref linkend="chapter-final-preps"/> carefully as it explains several
  important issues the developer should be aware of before beginning to
  work through <xref linkend="chapter-cross-tools"/> and
  beyond.</para>

  <para><xref linkend="chapter-cross-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&mdash;for example, to compile a compiler, you need a
  compiler.</para>

  <para>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.</para>

  <para>After we build our <quote>Cross-Tools</quote>, 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
  <xref linkend="chapter-temp-system"/>.</para>

  <para>In <xref linkend="chapter-building-system"/>, 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.</para>

  <para>The <command>chroot</command> (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 <quote>chrooting</quote> 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.</para>

  <para>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 <xref linkend="ch-boot-whatnext"/></para>

  <para>To finish the installation, the CLFS-Bootscripts are set up in <xref
  linkend="chapter-bootscripts"/>, and the kernel and boot loader are set
  up in <xref linkend="chapter-bootable"/>. <xref linkend="chapter-finalizing"/>
  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.</para>

  <para>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.</para>

</sect1>