source: BOOK/introduction/common/how.xml@ ca55789

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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
  Unix system or Linux distribution (such as Debian, Fedora, openSUSE,
  or Ubuntu). This existing 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 a livecd. Most distributions provide
  a livecd, which provides an environment to which you can add the required
  tools onto, allowing you to
  successfully follow the instructions in this book. Remember that if you
  reboot the livecd you will need to reconfigure the host environment before
  continuing with your build.</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
  <filename class="directory">/tools</filename>. This minimal system will be
  built using the cross-toolchain in
  <filename class="directory">/cross-tools</filename>.</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
  boot-scripts, and building a miminal kernel.<!-- We also describe some
  alternative booting methods in <xref linkend="ch-boot-whatnext"/> --></para>

  <para>To finish the installation, several configuration files are created in
  <xref linkend="chapter-system-config"/>, 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>