source: chapter06/kernel.xml@ 56f1739

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<sect1 id="ch-tools-kernel" role="wrap">
  <?dbhtml filename="kernel.html"?>

  <sect1info condition="script">
    <productname>kernel</productname>
    <productnumber>&linux-version;</productnumber>
    <address>&linux-url;</address>
  </sect1info>

  <title>Linux-&linux-version;</title>

  <indexterm zone="ch-tools-kernel">
    <primary sortas="a-Linux">Linux</primary>
    <secondary>tools</secondary>
  </indexterm>

  <sect2 role="package">
    <title/>

    <para>The Linux package contains the Linux kernel.</para>

    <segmentedlist>
      <segtitle>&buildtime;</segtitle>
      <segtitle>&diskspace;</segtitle>

      <seglistitem>
        <seg>&linux-tmp-sbu;</seg>
        <seg>&linux-tmp-du;</seg>
      </seglistitem>
    </segmentedlist>

  </sect2>

  <sect2 role="installation">
    <title>Installation of the kernel</title>

    <para>Building the kernel involves a few steps&mdash;configuration,
    compilation, and installation. Read the <filename>README</filename> file
    in the kernel source tree for alternative methods to the way this book
    configures the kernel.</para>

    <para>Prepare for compilation by running the following command:</para>

<screen><userinput remap="pre">make mrproper</userinput></screen>

    <para>This ensures that the kernel tree is absolutely clean. The
    kernel team recommends that this command be issued prior to each
    kernel compilation. Do not rely on the source tree being clean after
    un-tarring.</para>

    <para>There are several ways to configure the kernel options. Usually,
    This is done through a menu-driven interface, for example:</para>

<screen role="nodump"><userinput>make ARCH=<replaceable>x86</replaceable> CROSS_COMPILE=$LFS_TGT- menuconfig</userinput></screen>

    <variablelist>
      <title>The meaning of make environment variables:</title>

      <varlistentry>
        <term><command>ARCH=x86</command></term>
        <listitem>
          <para>Configure the kernel for running on the target machine.
          Replace <replaceable>x86</replaceable> with a value suitable
          for your target machine if it's not a 32-bit or 64-bit x86.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><command>CROSS_COMPILE=$LFS_TGT-</command></term>
        <listitem>
          <para>Build the kernel with Binutils and GCC built in
          <xref linkend='chapter-cross-tools'/>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><command>menuconfig</command></term>
        <listitem>
          <para>This launches an ncurses menu-driven interface. For other
          (graphical) interfaces, type <command>make help</command>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>(optional) <parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
        <listitem>
          <para>This establishes the locale setting to the one used on the
          host.  This may be needed for a proper menuconfig ncurses interface
          line drawing on a UTF-8 linux text console.</para>

          <para>If used, be sure to replace
          <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
          the <envar>$LANG</envar> variable from your host.  You can
          alternatively use instead the host's value of <envar>$LC_ALL</envar>
          or <envar>$LC_CTYPE</envar>.</para>
        </listitem>
      </varlistentry>

    </variablelist>

    <note>
    
      <para>A good starting place for setting up the kernel configuration is to
      run <command>make ARCH=x86 CROSS_COMPILE=$LFS_TGT- defconfig</command>. This will set the base
      configuration to a good state that takes your target system architecture
      into account.</para>

    </note>

      <para>Read <xref linkend='ch-bootable-kernel'/> for more information
      about kernel configuration.  You should enable or disable some kernel
      configuration options now:</para>

    <variablelist>
      <title>Kernel configuration options and explanation:</title>

      <varlistentry>
        <term>Set <parameter>CONFIG_MODULES=n</parameter></term>
        <listitem>
          <para>Modular kernel needs <command>modprobe</command> tool from
          <application>Kmod</application> to load modules, which is not
          installed in the temporary system.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Set <parameter>CONFIG_EXTRA_FIRMWARE="<replaceable>a.bin b.bin</replaceable>"</parameter></term>
        <listitem>
          <para>Build firmware blobs into the kernel.  Some drivers may
          require the firmwares to be in-kernel if the driver is not built
          as module.</para>
          <note>
            <para>
              The kernel binaries with third-party blobs are not
              distributable.  If you distribute such a kernel binary to
              others, you may violate GPL.  It's recommended to remove the
              temporary kernel image after you've successfully boot your LFS
              system with the new kernel image, which will be installed in
              <xref linkend="ch-bootable-kernel"/>.
            </para>
          </note>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Set <parameter>CONFIG_EXTRA_FIRMWARE_DIR="<replaceable>$LFS</replaceable>/lib/firmware"</parameter></term>
        <listitem>
          <para>The building system will search
          <filename class="directory">/lib/firmware</filename> for firmware
          blobs in <parameter>CONFIG_EXTRA_FIRMWARE</parameter>.  Note that
          you'll need to install the needed firmwares into
          <filename class="directory">$LFS/lib/firmware</filename> first,
          and manually replace <envar>$LFS</envar> with the value in
          configuration.  The firmwares in
          <filename class="directory">$LFS/lib/filename</filename> will be
          copied to the target machine along with the system, so kernel and
          kernel modules which will be built in
          <xref linkend="ch-bootable-kernel"/> can load them without
          <parameter>CONFIG_EXTRA_FIRMWARE</parameter>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>Enable <parameter>CONFIG_EXT2</parameter>,
                     <parameter>CONFIG_EXT4</parameter>,
                 and <parameter>CONFIG_VFAT_FS</parameter></term>
        <listitem>
          <para>They are needed to access the filesystems we'll make for the
          target system.</para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para>Compile the kernel image:</para>

<screen><userinput remap="make">make ARCH=x86 CROSS_COMPILE=$LFS_TGT-</userinput></screen>

    <para>Install the kernel image into the
    <filename class="directory">$LFS/boot</filename> directory:</para>

  <screen><userinput remap="install">install -vm644 vmlinux $LFS/boot/vmlinux</userinput></screen>

  </sect2>

  <sect2 role="content">
    <title/>

    <para>Details on this package are located in
    <xref linkend="contents-kernel" role="."/></para>

  </sect2>

</sect1>