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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % general-entities SYSTEM "../general.ent">
%general-entities;
]>
<sect1 id="ch-bootable-kernel" role="wrap">
<?dbhtml filename="kernel.html"?>
<title>Linux-&linux-version;</title>
<indexterm zone="ch-bootable-kernel">
<primary sortas="a-Linux">Linux</primary>
</indexterm>
<sect2 role="package">
<title/>
<para>The Linux package contains the Linux kernel.</para>
<segmentedlist>
<segtitle>&buildtime;</segtitle>
<segtitle>&diskspace;</segtitle>
<seglistitem>
<seg>&linux-ch8-sbu;</seg>
<seg>&linux-ch8-du;</seg>
</seglistitem>
</segmentedlist>
</sect2>
<sect2 role="installation">
<title>Installation of the kernel</title>
<para>Building the kernel involves a few steps—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>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>
<!-- Support for compiling a keymap into the kernel is deliberately removed -->
<para>Configure the kernel via a menu-driven interface. BLFS has some
information regarding particular kernel configuration requirements of
packages outside of LFS at <ulink
url="&blfs-root;view/svn/longindex.html#kernel-config-index"/>:</para>
<screen role="nodump"><userinput>make menuconfig</userinput></screen>
<para>Alternatively, <command>make oldconfig</command> may be more
appropriate in some situations. See the <filename>README</filename>
file for more information.</para>
<para>If desired, skip kernel configuration by copying the kernel
config file, <filename>.config</filename>, from the host system
(assuming it is available) to the unpacked <filename
class="directory">linux-&linux-version;</filename> directory. However,
we do not recommend this option. It is often better to explore all the
configuration menus and create the kernel configuration from
scratch.</para>
<para>Compile the kernel image and modules:</para>
<screen><userinput>make</userinput></screen>
<para>If using kernel modules, an <filename>/etc/modprobe.conf</filename>
file may be needed. Information pertaining to modules and kernel
configuration is located in <xref linkend="ch-scripts-udev"/> and in the
kernel documentation in the <filename
class="directory">linux-&linux-version;/Documentation</filename> directory.
Also, <filename>modprobe.conf(5)</filename> may be of interest.</para>
<para>Install the modules, if the kernel configuration uses them:</para>
<screen><userinput>make modules_install</userinput></screen>
<para>After kernel compilation is complete, additional steps are
required to complete the installation. Some files need to be copied to
the <filename class="directory">/boot</filename> directory.</para>
<para>The path to the kernel image may vary depending on the platform
being used. The following command assumes an x86 architecture:</para>
<screen><userinput>cp -v arch/i386/boot/bzImage /boot/lfskernel-&linux-version;</userinput></screen>
<para><filename>System.map</filename> is a symbol file for the kernel.
It maps the function entry points of every function in the kernel API,
as well as the addresses of the kernel data structures for the running
kernel. Issue the following command to install the map file:</para>
<screen><userinput>cp -v System.map /boot/System.map-&linux-version;</userinput></screen>
<para>The kernel configuration file <filename>.config</filename>
produced by the <command>make menuconfig</command> step
above contains all the configuration selections for the kernel
that was just compiled. It is a good idea to keep this file for future
reference:</para>
<screen><userinput>cp -v .config /boot/config-&linux-version;</userinput></screen>
<para>Install the documentation for the Linux kernel:</para>
<screen><userinput>install -d /usr/share/doc/linux-&linux-version; &&
cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
<para>It is important to note that the files in the kernel source
directory are not owned by <emphasis>root</emphasis>. Whenever a
package is unpacked as user <emphasis>root</emphasis> (like we did
inside chroot), the files have the user and group IDs of whatever
they were on the packager's computer. This is usually not a problem
for any other package to be installed because the source tree is
removed after the installation. However, the Linux source tree is
often retained for a long time. Because of this, there is a chance
that whatever user ID the packager used will be assigned to somebody
on the machine. That person would then have write access to the kernel
source.</para>
<para>If the kernel source tree is going to be retained, run
<command>chown -R 0:0</command> on the <filename
class="directory">linux-&linux-version;</filename> directory to ensure
all files are owned by user <emphasis>root</emphasis>.</para>
<warning>
<para>Some kernel documentation recommends creating a symlink from
<filename class="symlink">/usr/src/linux</filename> pointing to the kernel
source directory. This is specific to kernels prior to the 2.6 series and
<emphasis>must not</emphasis> be created on an LFS system as it can cause
problems for packages you may wish to build once your base LFS system is
complete.</para>
<para>Also, the headers in the system's
<filename class="directory">include</filename> directory should
<emphasis>always</emphasis> be the ones against which Glibc was compiled,
that is, the sanitised headers from the Linux kernel tarball, and
therefore, should <emphasis>never</emphasis> be replaced by the raw kernel
headers.</para>
</warning>
</sect2>
<sect2 id="contents-kernel" role="content">
<title>Contents of Linux</title>
<segmentedlist>
<segtitle>Installed files</segtitle>
<seglistitem>
<seg>config-&linux-version;, lfskernel-&linux-version;, and
System.map-&linux-version;</seg>
</seglistitem>
</segmentedlist>
<variablelist>
<bridgehead renderas="sect3">Short Descriptions</bridgehead>
<?dbfo list-presentation="list"?>
<?dbhtml list-presentation="table"?>
<varlistentry id="config">
<term><filename>config-&linux-version;</filename></term>
<listitem>
<para>Contains all the configuration selections for the kernel</para>
<indexterm zone="ch-bootable-kernel config">
<primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="lfskernel">
<term><filename>lfskernel-&linux-version;</filename></term>
<listitem>
<para>The engine of the Linux system. When turning on the computer,
the kernel is the first part of the operating system that gets loaded.
It detects and initializes all components of the computer's hardware,
then makes these components available as a tree of files to the
software and turns a single CPU into a multitasking machine capable
of running scores of programs seemingly at the same time</para>
<indexterm zone="ch-bootable-kernel lfskernel">
<primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
</indexterm>
</listitem>
</varlistentry>
<varlistentry id="System.map">
<term><filename>System.map-&linux-version;</filename></term>
<listitem>
<para>A list of addresses and symbols; it maps the entry points and
addresses of all the functions and data structures in the
kernel</para>
<indexterm zone="ch-bootable-kernel System.map">
<primary sortas="e-/boot/System.map">/boot/System.map-&linux-version;</primary>
</indexterm>
</listitem>
</varlistentry>
</variablelist>
</sect2>
</sect1>
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