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https://git.linuxfromscratch.org/lfs.git
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201aa93863
We are using American rule for punctuation/comma vs. quotes. We've fixed most cases but not <xref>s.
521 lines
21 KiB
XML
521 lines
21 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-bootable-kernel" role="wrap">
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<?dbhtml filename="kernel.html"?>
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<sect1info condition="script">
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<productname>kernel</productname>
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<productnumber>&linux-version;</productnumber>
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<address>&linux-url;</address>
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</sect1info>
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<title>Linux-&linux-version;</title>
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<indexterm zone="ch-bootable-kernel">
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<primary sortas="a-Linux">Linux</primary>
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</indexterm>
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<sect2 role="package">
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<title/>
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<para>The Linux package contains the Linux kernel.</para>
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<segmentedlist>
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<segtitle>&buildtime;</segtitle>
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<segtitle>&diskspace;</segtitle>
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<seglistitem>
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<seg>&linux-knl-sbu;</seg>
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<seg>&linux-knl-du;</seg>
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</seglistitem>
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</segmentedlist>
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</sect2>
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<sect2 role="installation">
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<title>Installation of the kernel</title>
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<para>Building the kernel involves a few steps—configuration,
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compilation, and installation. Read the <filename>README</filename> file
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in the kernel source tree for alternative methods to the way this book
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configures the kernel.</para>
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<important>
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<para>
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Building the linux kernel for the first time is one of the most
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challenging tasks in LFS. Getting it right depends on the specific
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hardware for the target system and your specific needs. There are
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almost 12,000 configuration items that are available for the kernel
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although only about a third of them are needed for most computers. The
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LFS editors recommend that users not familiar with this process follow
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the procedures below fairly closely. The objective is to get an
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initial system to a point where you can log in at the command line when
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you reboot later in <xref linkend="ch-finish-reboot" role='.'/>
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At this point optimization and customization is not a goal.
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</para>
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<para>
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For general information on kernel configuration see <ulink
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url="&hints-root;kernel-configuration.txt"/>. Additional information
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about configuring and building the kernel can be found at <ulink
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url="&anduin-sources;/kernel-nutshell/"/>.
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These references are a bit
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dated, but still give a reasonable overview of the process.
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</para>
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<para>
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If all else fails, you can ask for help on the <ulink
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url="https://www.linuxfromscratch.org/mail.html">lfs-support</ulink>
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mailing list. Note that subscribing is required in order for the list
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to avoid spam.
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</para>
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</important>
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<para>Prepare for compilation by running the following command:</para>
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<screen><userinput remap="pre">make mrproper</userinput></screen>
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<para>This ensures that the kernel tree is absolutely clean. The
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kernel team recommends that this command be issued prior to each
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kernel compilation. Do not rely on the source tree being clean after
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un-tarring.</para>
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<para>There are several ways to configure the kernel options. Usually,
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this is done through a menu-driven interface, for example:</para>
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<screen role="nodump"><userinput>make menuconfig</userinput></screen>
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<variablelist>
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<title>The meaning of optional make environment variables:</title>
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<varlistentry>
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<term><parameter>LANG=<host_LANG_value> LC_ALL=</parameter></term>
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<listitem>
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<para>This establishes the locale setting to the one used on the
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host. This may be needed for a proper menuconfig ncurses interface
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line drawing on a UTF-8 linux text console.</para>
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<para>If used, be sure to replace
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<replaceable><host_LANG_value></replaceable> by the value of
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the <envar>$LANG</envar> variable from your host. You can
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alternatively use instead the host's value of <envar>$LC_ALL</envar>
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or <envar>$LC_CTYPE</envar>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>make menuconfig</command></term>
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<listitem>
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<para>This launches an ncurses menu-driven interface. For other
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(graphical) interfaces, type <command>make help</command>.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<!-- Support for compiling a keymap into the kernel is deliberately removed -->
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<note>
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<?dbfo keep-together="auto"?>
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<para>A good starting place for setting up the kernel configuration is to
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run <command>make defconfig</command>. This will set the base
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configuration to a good state that takes your current system architecture
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into account.</para>
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<para>Be sure to enable/disable/set the following features or the system might
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not work correctly or boot at all:</para>
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<!-- To editors: for updating kernel configuration, edit
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kernel/*.toml and regenerate kernel/*.xml with
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"make -C kernel KERNEL_TREE=</usr/src/linux-&linux-version> -->
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
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href="kernel/sysv.xml"/>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
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href="kernel/systemd.xml"/>
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<para>Enable some additional features if you are building a 64-bit
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system. If you are using menuconfig, enable them in the order of
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<parameter>CONFIG_PCI_MSI</parameter> first, then
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<parameter>CONFIG_IRQ_REMAP</parameter>, at last
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<parameter>CONFIG_X86_X2APIC</parameter> because an option only
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shows up after its dependencies are selected.</para>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
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href="kernel/x2apic.xml"/>
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<para>If you are building a 32-bit system running on a hardware
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with RAM more than 4GB, adjust the configuration so the kernel will
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be able to use up to 64GB physical RAM:</para>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
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href="kernel/highmem.xml"/>
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<para>If the partition for the LFS system is in a NVME SSD (i. e. the
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device node for the partition is <filename>/dev/nvme*</filename>
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instead of <filename>/dev/sd*</filename>), enable NVME support or
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the LFS system won't boot:</para>
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<xi:include xmlns:xi="http://www.w3.org/2001/XInclude"
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href="kernel/nvme.xml"/>
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</note>
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<note revision="systemd">
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<para>While "The IPv6 Protocol" is not strictly
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required, it is highly recommended by the systemd developers.</para>
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</note>
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<para>There are several other options that may be desired
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depending on the requirements for the system. For a list of options needed
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for BLFS packages, see the <ulink
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url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
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Index of Kernel Settings</ulink>.</para>
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<note>
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<para>If your host hardware is using UEFI and you wish to boot the
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LFS system with it, you should adjust some kernel configuration
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following <ulink url="&blfs-book;postlfs/grub-setup.html#uefi-kernel">
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the BLFS page</ulink> <emphasis role='bold'>even if you'll use the
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UEFI bootloader from the host distro</emphasis>.</para>
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</note>
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<variablelist>
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<title>The rationale for the above configuration items:</title>
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<varlistentry>
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<term><parameter>Randomize the address of the kernel image (KASLR)</parameter></term>
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<listitem>
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<para>Enable ASLR for kernel image, to mitigate some attacks based
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on fixed addresses of sensitive data or code in the kernel.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<parameter>
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Compile the kernel with warnings as errors
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</parameter>
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</term>
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<listitem>
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<para>This may cause building failure if the compiler and/or
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configuration are different from those of the kernel
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developers.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<parameter>
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Enable kernel headers through /sys/kernel/kheaders.tar.xz
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</parameter>
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</term>
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<listitem>
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<para>This will require <command>cpio</command> building the kernel.
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<command>cpio</command> is not installed by LFS.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<parameter>
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Configure standard kernel features (expert users)
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</parameter>
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</term>
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<listitem>
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<para>This will make some options show up in the configuration
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interface but changing those options may be dangerous. Do not use
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this unless you know what you are doing.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>Strong Stack Protector</parameter></term>
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<listitem>
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<para>Enable SSP for the kernel. We've enabled it for the entire
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userspace with <parameter>--enable-default-ssp</parameter>
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configuring GCC, but the kernel does not use GCC default setting
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for SSP. We enable it explicitly here.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>Support for uevent helper</parameter></term>
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<listitem>
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<para>Having this option set may interfere with device
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management when using Udev.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>Maintain a devtmpfs</parameter></term>
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<listitem>
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<para>This will create automated device nodes which are populated by the
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kernel, even without Udev running. Udev then runs on top of this,
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managing permissions and adding symlinks. This configuration
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item is required for all users of Udev.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>Automount devtmpfs at /dev</parameter></term>
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<listitem>
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<para>This will mount the kernel view of the devices on /dev
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upon switching to root filesystem just before starting
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init.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<parameter>
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Enable legacy fbdev support for your modesetting driver
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</parameter> and
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<parameter>Framebuffer Console support</parameter>
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</term>
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<listitem>
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<para>These are needed to display the Linux console on a
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GPU driven by a DRI (Direct Rendering Infrastructure) driver.
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If <option>CONFIG_DRM</option> (Direct Rendering Manager) is
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enabled, you should enable these two options as well or you'll see
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a blank screen once the DRI driver is loaded.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>Support x2apic</parameter></term>
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<listitem>
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<para>Support running the interrupt controller of 64-bit x86
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processors in x2APIC mode. x2APIC may be enabled by firmware on
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64-bit x86 systems, and a kernel without this option enabled will
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panic on boot if x2APIC is enabled by firmware. This option
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has no effect, but also does no harm if x2APIC is disabled by the
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firmware.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>Alternatively, <command>make oldconfig</command> may be more
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appropriate in some situations. See the <filename>README</filename>
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file for more information.</para>
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<para>If desired, skip kernel configuration by copying the kernel
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config file, <filename>.config</filename>, from the host system
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(assuming it is available) to the unpacked <filename
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class="directory">linux-&linux-version;</filename> directory. However,
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we do not recommend this option. It is often better to explore all the
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configuration menus and create the kernel configuration from
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scratch.</para>
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<para>Compile the kernel image and modules:</para>
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<screen><userinput remap="make">make</userinput></screen>
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<para>If using kernel modules, module configuration in <filename
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class="directory">/etc/modprobe.d</filename> may be required.
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Information pertaining to modules and kernel configuration is
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located in <xref linkend="ch-config-udev"/> and in the kernel
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documentation in the <filename
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class="directory">linux-&linux-version;/Documentation</filename> directory.
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Also, <ulink role='man' url='&man;modprobe.d.5'>modprobe.d(5)</ulink>
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may be of interest.</para>
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<para>Unless module support has been disabled in the kernel configuration,
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install the modules with:</para>
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<screen><userinput remap="install">make modules_install</userinput></screen>
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<para>After kernel compilation is complete, additional steps are
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required to complete the installation. Some files need to be copied to
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the <filename class="directory">/boot</filename> directory.</para>
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<caution>
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<para>If you've decided to use a separate &boot-dir; partition for the
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LFS system (maybe sharing a &boot-dir; partition with the host
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distro) , the files copied below should go there. The easiest way to
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do that is to create the entry for &boot-dir; in &fstab; first (read
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the previous section for details), then issue the following command
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as the &root; user in the
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<emphasis>chroot environment</emphasis>:</para>
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<screen role="nodump"><userinput>mount /boot</userinput></screen>
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<para>The path to the device node is omitted in the command because
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<command>mount</command> can read it from &fstab;.</para>
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</caution>
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<para>The path to the kernel image may vary depending on the platform being
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used. The filename below can be changed to suit your taste, but the stem of
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the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
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the automatic setup of the boot process described in the next section. The
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following command assumes an x86 architecture:</para>
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<screen><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
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<para><filename>System.map</filename> is a symbol file for the kernel.
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It maps the function entry points of every function in the kernel API,
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as well as the addresses of the kernel data structures for the running
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kernel. It is used as a resource when investigating kernel problems.
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Issue the following command to install the map file:</para>
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<screen><userinput remap="install">cp -iv System.map /boot/System.map-&linux-version;</userinput></screen>
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<para>The kernel configuration file <filename>.config</filename>
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produced by the <command>make menuconfig</command> step
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above contains all the configuration selections for the kernel
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that was just compiled. It is a good idea to keep this file for future
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reference:</para>
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<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
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<para>Install the documentation for the Linux kernel:</para>
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<screen><userinput remap="install">cp -r Documentation -T /usr/share/doc/linux-&linux-version;</userinput></screen>
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<para>It is important to note that the files in the kernel source
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directory are not owned by <emphasis>root</emphasis>. Whenever a
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package is unpacked as user <emphasis>root</emphasis> (like we did
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inside chroot), the files have the user and group IDs of whatever
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they were on the packager's computer. This is usually not a problem
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for any other package to be installed because the source tree is
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removed after the installation. However, the Linux source tree is
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often retained for a long time. Because of this, there is a chance
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that whatever user ID the packager used will be assigned to somebody
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on the machine. That person would then have write access to the kernel
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source.</para>
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<note>
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<para>In many cases, the configuration of the kernel will need to be
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updated for packages that will be installed later in BLFS. Unlike
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other packages, it is not necessary to remove the kernel source tree
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after the newly built kernel is installed.</para>
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<para>If the kernel source tree is going to be retained, run
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<command>chown -R 0:0</command> on the <filename
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class="directory">linux-&linux-version;</filename> directory to ensure
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all files are owned by user <emphasis>root</emphasis>.</para>
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</note>
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<warning>
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<para>Some kernel documentation recommends creating a symlink from
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<filename class="symlink">/usr/src/linux</filename> pointing to the kernel
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source directory. This is specific to kernels prior to the 2.6 series and
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<emphasis>must not</emphasis> be created on an LFS system as it can cause
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problems for packages you may wish to build once your base LFS system is
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complete.</para>
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</warning>
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<warning>
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<para>The headers in the system's <filename
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class="directory">include</filename> directory (<filename
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class="directory">/usr/include</filename>) should
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<emphasis>always</emphasis> be the ones against which Glibc was compiled,
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that is, the sanitised headers installed in <xref
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linkend="ch-tools-linux-headers"/>. Therefore, they should
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<emphasis>never</emphasis> be replaced by either the raw kernel headers
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or any other kernel sanitized headers.</para>
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</warning>
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</sect2>
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<sect2 id="conf-modprobe" role="configuration">
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<title>Configuring Linux Module Load Order</title>
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<indexterm zone="conf-modprobe">
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<primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
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</indexterm>
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<para>Most of the time Linux modules are loaded automatically, but
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sometimes it needs some specific direction. The program that loads
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modules, <command>modprobe</command> or <command>insmod</command>, uses
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<filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
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needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
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uhci_hcd) have been built as modules, they will be loaded in the correct
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order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
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to avoid a warning being output at boot time.</para>
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<para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
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the following:</para>
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<screen><userinput>install -v -m755 -d /etc/modprobe.d
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cat > /etc/modprobe.d/usb.conf << "EOF"
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<literal># Begin /etc/modprobe.d/usb.conf
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install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
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install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
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# End /etc/modprobe.d/usb.conf</literal>
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EOF</userinput></screen>
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</sect2>
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<sect2 id="contents-kernel" role="content">
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<title>Contents of Linux</title>
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<segmentedlist>
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<segtitle>Installed files</segtitle>
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<segtitle>Installed directories</segtitle>
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<seglistitem>
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<seg>config-&linux-version;,
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vmlinuz-&linux-version;-lfs-&version;,
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and System.map-&linux-version;</seg>
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<seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
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</seglistitem>
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</segmentedlist>
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<variablelist>
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<bridgehead renderas="sect3">Short Descriptions</bridgehead>
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<?dbfo list-presentation="list"?>
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<?dbhtml list-presentation="table"?>
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<varlistentry id="config">
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<term><filename>config-&linux-version;</filename></term>
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<listitem>
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<para>Contains all the configuration selections for the kernel</para>
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<indexterm zone="ch-bootable-kernel config">
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<primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
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</indexterm>
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</listitem>
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</varlistentry>
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<varlistentry id="lfskernel">
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<term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
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<listitem>
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<para>The engine of the Linux system. When turning on the computer,
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the kernel is the first part of the operating system that gets loaded.
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It detects and initializes all components of the computer's hardware,
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then makes these components available as a tree of files to the
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software and turns a single CPU into a multitasking machine capable
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of running scores of programs seemingly at the same time</para>
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<indexterm zone="ch-bootable-kernel lfskernel">
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<primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
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</indexterm>
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</listitem>
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</varlistentry>
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<varlistentry id="System.map">
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<term><filename>System.map-&linux-version;</filename></term>
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<listitem>
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<para>A list of addresses and symbols; it maps the entry points and
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addresses of all the functions and data structures in the
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kernel</para>
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<indexterm zone="ch-bootable-kernel System.map">
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<primary sortas="e-/boot/System.map">/boot/System.map-&linux-version;</primary>
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</indexterm>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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</sect1>
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