| 1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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| 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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| 4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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| 5 | %general-entities;
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| 6 | ]>
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| 7 |
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| 8 | <sect1 id="ch-bootable-kernel" role="wrap">
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| 9 | <?dbhtml filename="kernel.html"?>
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| 10 |
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| 11 | <sect1info condition="script">
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| 12 | <productname>linux</productname>
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| 13 | <productnumber>&linux-version;</productnumber>
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| 14 | <address>&linux-url;</address>
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| 15 | </sect1info>
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| 16 |
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| 17 | <title>Linux-&linux-version;</title>
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| 18 |
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| 19 | <indexterm zone="ch-bootable-kernel">
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| 20 | <primary sortas="a-Linux">Linux</primary>
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| 21 | </indexterm>
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| 22 |
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| 23 | <sect2 role="package">
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| 24 | <title/>
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| 25 |
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| 26 | <para>The Linux package contains the Linux kernel.</para>
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| 27 |
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| 28 | <segmentedlist>
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| 29 | <segtitle>&buildtime;</segtitle>
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| 30 | <segtitle>&diskspace;</segtitle>
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| 31 |
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| 32 | <seglistitem>
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| 33 | <seg>&linux-ch8-sbu;</seg>
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| 34 | <seg>&linux-ch8-du;</seg>
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| 35 | </seglistitem>
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| 36 | </segmentedlist>
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| 37 |
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| 38 | </sect2>
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| 39 |
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| 40 | <sect2 role="installation">
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| 41 | <title>Installation of the kernel</title>
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| 42 |
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| 43 | <para>Building the kernel involves a few steps—configuration,
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| 44 | compilation, and installation. Read the <filename>README</filename> file
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| 45 | in the kernel source tree for alternative methods to the way this book
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| 46 | configures the kernel.</para>
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| 47 |
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| 48 | <para>Prepare for compilation by running the following command:</para>
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| 49 |
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| 50 | <screen><userinput remap="pre">make mrproper</userinput></screen>
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| 51 |
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| 52 | <para>This ensures that the kernel tree is absolutely clean. The
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| 53 | kernel team recommends that this command be issued prior to each
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| 54 | kernel compilation. Do not rely on the source tree being clean after
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| 55 | un-tarring.</para>
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| 56 |
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| 57 | <!-- Support for compiling a keymap into the kernel is deliberately removed -->
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| 58 |
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| 59 | <para>Configure the kernel via a menu-driven interface. For general
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| 60 | information on kernel configuration see <ulink
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| 61 | url="&hints-root;kernel-configuration.txt"/>. BLFS has some information
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| 62 | regarding particular kernel configuration requirements of packages outside
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| 63 | of LFS at <ulink
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| 64 | url="&blfs-root;view/svn/longindex.html#kernel-config-index"/>. Additional
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| 65 | information about configuring and building the kernel can be found at
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| 66 | <ulink url="http://www.kroah.com/lkn/"/> </para>
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| 67 |
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| 68 | <note><para>A good starting place for setting up the kernel configuration
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| 69 | is to run <command>make defconfig</command>. This will set the base
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| 70 | configuration to a good state that takes your current system architecture
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| 71 | into account.</para>
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| 72 |
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| 73 | <para>Be sure to enable or disable following features or the system might not
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| 74 | work correctly or boot at all:</para>
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| 75 |
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| 76 | <screen role="nodump">General setup --->
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| 77 | [*] open by fhandle syscalls
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| 78 | [*] Control Group support
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| 79 | Processor type and features --->
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| 80 | [*] Enable seccomp to safely compute untrusted bytecode
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| 81 | Networking support --->
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| 82 | Networking options --->
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| 83 | <*> The IPv6 protocol
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| 84 | Device Drivers --->
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| 85 | Generic Driver Options --->
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| 86 | () path to uevent helper
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| 87 | [*] Maintain a devtmpfs filesystem to mount at /dev
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| 88 | [ ] Fallback user-helper invocation for firmware loading
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| 89 | File systems --->
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| 90 | [*] Inotify support for userspace
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| 91 | <*> Kernel automounter version 4 support (also supports v3)
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| 92 | Pseudo filesystems --->
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| 93 | [*] Tmpfs POSIX Access Control Lists
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| 94 | [*] Tmpfs extended attributes</screen></note>
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| 95 |
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| 96 | <note><para>While "The IPv6 Protocol" is not strictly required, it is
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| 97 | highly recommended by the Systemd developers.</para></note>
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| 98 |
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| 99 | <screen role="nodump"><userinput>make LANG=<replaceable><host_LANG_value></replaceable> LC_ALL= menuconfig</userinput></screen>
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| 100 |
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| 101 | <variablelist>
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| 102 | <title>The meaning of the make parameters:</title>
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| 103 |
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| 104 | <varlistentry>
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| 105 | <term><parameter>LANG=<host_LANG_value> LC_ALL=</parameter></term>
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| 106 | <listitem>
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| 107 | <para>This establishes the locale setting to the one used on the host.
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| 108 | This is needed for a proper menuconfig ncurses interface line
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| 109 | drawing on UTF-8 linux text console.</para>
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| 110 |
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| 111 | <para>Be sure to replace <replaceable><host_LANG_value></replaceable>
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| 112 | by the value of the <envar>$LANG</envar> variable from your host.
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| 113 | If not set, you could use instead the host's value of <envar>$LC_ALL</envar>
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| 114 | or <envar>$LC_CTYPE</envar>.</para>
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| 115 | </listitem>
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| 116 | </varlistentry>
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| 117 |
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| 118 | </variablelist>
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| 119 |
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| 120 | <para>Alternatively, <command>make oldconfig</command> may be more
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| 121 | appropriate in some situations. See the <filename>README</filename>
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| 122 | file for more information.</para>
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| 123 |
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| 124 | <para>If desired, skip kernel configuration by copying the kernel
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| 125 | config file, <filename>.config</filename>, from the host system
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| 126 | (assuming it is available) to the unpacked <filename
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| 127 | class="directory">linux-&linux-version;</filename> directory. However,
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| 128 | we do not recommend this option. It is often better to explore all the
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| 129 | configuration menus and create the kernel configuration from
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| 130 | scratch.</para>
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| 131 |
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| 132 | <para>Compile the kernel image and modules:</para>
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| 133 |
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| 134 | <screen><userinput remap="make">make</userinput></screen>
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| 135 |
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| 136 | <para>If using kernel modules, module configuration in <filename
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| 137 | class="directory">/etc/modprobe.d</filename> may be required.
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| 138 | Information pertaining to modules and kernel configuration is
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| 139 | located in <xref linkend="ch-scripts-udev"/> and in the kernel
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| 140 | documentation in the <filename
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| 141 | class="directory">linux-&linux-version;/Documentation</filename> directory.
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| 142 | Also, <filename>modprobe.conf(5)</filename> may be of interest.</para>
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| 143 |
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| 144 | <para>Install the modules, if the kernel configuration uses them:</para>
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| 145 |
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| 146 | <screen><userinput remap="install">make modules_install</userinput></screen>
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| 147 |
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| 148 | <para>After kernel compilation is complete, additional steps are
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| 149 | required to complete the installation. Some files need to be copied to
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| 150 | the <filename class="directory">/boot</filename> directory.</para>
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| 151 |
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| 152 | <para>The path to the kernel image may vary depending on the platform being
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| 153 | used. The filename below can be changed to suit your taste, but the stem of
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| 154 | the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
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| 155 | the automatic setup of the boot process described in the next section. The
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| 156 | following command assumes an x86 architecture:</para>
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| 157 |
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| 158 | <screen><userinput remap="install">cp -v arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
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| 159 |
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| 160 | <para><filename>System.map</filename> is a symbol file for the kernel.
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| 161 | It maps the function entry points of every function in the kernel API,
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| 162 | as well as the addresses of the kernel data structures for the running
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| 163 | kernel. It is used as a resource when investigating kernel problems.
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| 164 | Issue the following command to install the map file:</para>
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| 165 |
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| 166 | <screen><userinput remap="install">cp -v System.map /boot/System.map-&linux-version;</userinput></screen>
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| 167 |
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| 168 | <para>The kernel configuration file <filename>.config</filename>
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| 169 | produced by the <command>make menuconfig</command> step
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| 170 | above contains all the configuration selections for the kernel
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| 171 | that was just compiled. It is a good idea to keep this file for future
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| 172 | reference:</para>
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| 173 |
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| 174 | <screen><userinput remap="install">cp -v .config /boot/config-&linux-version;</userinput></screen>
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| 175 |
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| 176 | <para>Install the documentation for the Linux kernel:</para>
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| 177 |
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| 178 | <screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
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| 179 | cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
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| 180 |
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| 181 | <para>It is important to note that the files in the kernel source
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| 182 | directory are not owned by <emphasis>root</emphasis>. Whenever a
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| 183 | package is unpacked as user <emphasis>root</emphasis> (like we did
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| 184 | inside chroot), the files have the user and group IDs of whatever
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| 185 | they were on the packager's computer. This is usually not a problem
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| 186 | for any other package to be installed because the source tree is
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| 187 | removed after the installation. However, the Linux source tree is
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| 188 | often retained for a long time. Because of this, there is a chance
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| 189 | that whatever user ID the packager used will be assigned to somebody
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| 190 | on the machine. That person would then have write access to the kernel
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| 191 | source.</para>
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| 192 |
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| 193 | <para>If the kernel source tree is going to be retained, run
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| 194 | <command>chown -R 0:0</command> on the <filename
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| 195 | class="directory">linux-&linux-version;</filename> directory to ensure
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| 196 | all files are owned by user <emphasis>root</emphasis>.</para>
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| 197 |
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| 198 | <warning>
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| 199 | <para>Some kernel documentation recommends creating a symlink from
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| 200 | <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
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| 201 | source directory. This is specific to kernels prior to the 2.6 series and
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| 202 | <emphasis>must not</emphasis> be created on an LFS system as it can cause
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| 203 | problems for packages you may wish to build once your base LFS system is
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| 204 | complete.</para>
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| 205 | </warning>
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| 206 |
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| 207 | <warning>
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| 208 | <para>The headers in the system's <filename
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| 209 | class="directory">include</filename> directory (<filename
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| 210 | class="directory">/usr/include</filename>) should
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| 211 | <emphasis>always</emphasis> be the ones against which Glibc was compiled,
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| 212 | that is, the sanitised headers installed in <xref
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| 213 | linkend="ch-system-linux-headers"/>. Therefore, they should
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| 214 | <emphasis>never</emphasis> be replaced by either the raw kernel headers
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| 215 | or any other kernel sanitized headers.</para>
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| 216 | </warning>
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| 217 |
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| 218 | </sect2>
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| 219 |
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| 220 | <sect2 id="conf-modprobe" role="configuration">
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| 221 | <title>Configuring Linux Module Load Order</title>
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| 222 |
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| 223 | <indexterm zone="conf-modprobe">
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| 224 | <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
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| 225 | </indexterm>
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| 226 |
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| 227 | <para>Most of the time Linux modules are loaded automatically, but
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| 228 | sometimes it needs some specific direction. The program that loads
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| 229 | modules, <command>modprobe</command> or <command>insmod</command>, uses
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| 230 | <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
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| 231 | needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
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| 232 | uhci_hcd) have been built as modules, they will be loaded in the correct
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| 233 | order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
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| 234 | to avoid a warning being output at boot time.</para>
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| 235 |
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| 236 | <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
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| 237 | the following:</para>
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| 238 |
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| 239 | <screen><userinput>install -v -m755 -d /etc/modprobe.d
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| 240 | cat > /etc/modprobe.d/usb.conf << "EOF"
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| 241 | <literal># Begin /etc/modprobe.d/usb.conf
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| 242 |
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| 243 | install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
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| 244 | install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
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| 245 |
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| 246 | # End /etc/modprobe.d/usb.conf</literal>
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| 247 | EOF</userinput></screen>
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| 248 |
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| 249 | </sect2>
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| 250 |
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| 251 | <sect2 id="contents-kernel" role="content">
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| 252 | <title>Contents of Linux</title>
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| 253 |
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| 254 | <segmentedlist>
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| 255 | <segtitle>Installed files</segtitle>
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| 256 | <segtitle>Installed directories</segtitle>
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| 257 |
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| 258 | <seglistitem>
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| 259 | <seg>config-&linux-version;,
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| 260 | vmlinuz-&linux-version;-lfs-&version;, and
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| 261 | System.map-&linux-version;</seg>
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| 262 | <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
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| 263 | </seglistitem>
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| 264 | </segmentedlist>
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| 265 |
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| 266 | <variablelist>
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| 267 | <bridgehead renderas="sect3">Short Descriptions</bridgehead>
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| 268 | <?dbfo list-presentation="list"?>
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| 269 | <?dbhtml list-presentation="table"?>
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| 270 |
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| 271 | <varlistentry id="config">
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| 272 | <term><filename>config-&linux-version;</filename></term>
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| 273 | <listitem>
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| 274 | <para>Contains all the configuration selections for the kernel</para>
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| 275 | <indexterm zone="ch-bootable-kernel config">
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| 276 | <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
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| 277 | </indexterm>
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| 278 | </listitem>
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| 279 | </varlistentry>
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| 280 |
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| 281 | <varlistentry id="lfskernel">
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| 282 | <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
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| 283 | <listitem>
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| 284 | <para>The engine of the Linux system. When turning on the computer,
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| 285 | the kernel is the first part of the operating system that gets loaded.
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| 286 | It detects and initializes all components of the computer's hardware,
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| 287 | then makes these components available as a tree of files to the
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| 288 | software and turns a single CPU into a multitasking machine capable
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| 289 | of running scores of programs seemingly at the same time</para>
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| 290 | <indexterm zone="ch-bootable-kernel lfskernel">
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| 291 | <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
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| 292 | </indexterm>
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| 293 | </listitem>
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| 294 | </varlistentry>
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| 295 |
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| 296 | <varlistentry id="System.map">
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| 297 | <term><filename>System.map-&linux-version;</filename></term>
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| 298 | <listitem>
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| 299 | <para>A list of addresses and symbols; it maps the entry points and
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| 300 | addresses of all the functions and data structures in the
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| 301 | kernel</para>
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| 302 | <indexterm zone="ch-bootable-kernel System.map">
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| 303 | <primary sortas="e-/boot/System.map">/boot/System.map-&linux-version;</primary>
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| 304 | </indexterm>
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| 305 | </listitem>
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| 306 | </varlistentry>
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| 307 |
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| 308 | </variablelist>
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| 309 |
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| 310 | </sect2>
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| 311 |
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| 312 | </sect1>
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