source: chapter08/kernel.xml@ 54a6bc9

multilib-10.1 multilib-before-cross
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1<?xml version="1.0" encoding="ISO-8859-1"?>
2<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "" [
4 <!ENTITY % general-entities SYSTEM "../general.ent">
5 %general-entities;
8<sect1 id="ch-bootable-kernel" role="wrap">
9 <?dbhtml filename="kernel.html"?>
11 <sect1info condition="script">
12 <productname>kernel</productname>
13 <productnumber>&linux-version;</productnumber>
14 <address>&linux-url;</address>
15 </sect1info>
17 <title>Linux-&linux-version;</title>
19 <indexterm zone="ch-bootable-kernel">
20 <primary sortas="a-Linux">Linux</primary>
21 </indexterm>
23 <sect2 role="package">
24 <title/>
26 <para>The Linux package contains the Linux kernel.</para>
28 <segmentedlist>
29 <segtitle>&buildtime;</segtitle>
30 <segtitle>&diskspace;</segtitle>
32 <seglistitem>
33 <seg>&linux-ch8-sbu;</seg>
34 <seg>&linux-ch8-du;</seg>
35 </seglistitem>
36 </segmentedlist>
38 </sect2>
40 <sect2 role="installation">
41 <title>Installation of the kernel</title>
43 <para>Building the kernel involves a few steps&mdash;configuration,
44 compilation, and installation. Read the <filename>README</filename> file
45 in the kernel source tree for alternative methods to the way this book
46 configures the kernel.</para>
48 <para>Prepare for compilation by running the following command:</para>
50<screen><userinput remap="pre">make mrproper</userinput></screen>
52 <para>This ensures that the kernel tree is absolutely clean. The
53 kernel team recommends that this command be issued prior to each
54 kernel compilation. Do not rely on the source tree being clean after
55 un-tarring.</para>
57 <!-- Support for compiling a keymap into the kernel is deliberately removed -->
59 <para>Configure the kernel via a menu-driven interface. For general
60 information on kernel configuration see <ulink
61 url="&hints-root;kernel-configuration.txt"/>. BLFS has some information
62 regarding particular kernel configuration requirements of packages outside
63 of LFS at <ulink
64 url="&blfs-book;longindex.html#kernel-config-index"/>. Additional
65 information about configuring and building the kernel can be found at
66 <ulink url=""/> </para>
68 <note>
70 <para>A good starting place for setting up the kernel configuration is to
71 run <command>make defconfig</command>. This will set the base
72 configuration to a good state that takes your current system architecture
73 into account.</para>
75 <para>Be sure to enable/disable/set the following features or the system might
76 not work correctly or boot at all:</para>
78 <screen role="nodump" revision="sysv">
79Device Drivers ---&gt;
80 Generic Driver Options ---&gt;
81 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
82 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
84Kernel hacking ---&gt;
85 Choose kernel unwinder (Frame pointer unwinder) ---&gt; [CONFIG_UNWINDER_FRAME_POINTER]</screen>
87 <screen role="nodump" revision="systemd">
88General setup -->
89 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
90 [*] Configure standard kernel features (expert users) [CONFIG_EXPERT] ---&gt;
91 [*] open by fhandle syscalls [CONFIG_FHANDLE]
92 [ ] Auditing support [CONFIG_AUDIT]
93 [*] Control Group support [CONFIG_CGROUPS]
94Processor type and features ---&gt;
95 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
96Firmware Drivers ---&gt;
97 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
98Networking support ---&gt;
99 Networking options ---&gt;
100 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
101Device Drivers ---&gt;
102 Generic Driver Options ---&gt;
103 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
104 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
105 Firmware Loader ---&gt;
106 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
107File systems ---&gt;
108 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
109 &lt;*&gt; Kernel automounter support (supports v3, v4, and v5) [CONFIG_AUTOFS_FS]
110 Pseudo filesystems ---&gt;
111 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]
112 [*] Tmpfs extended attributes [CONFIG_TMPFS_XATTR]
113Kernel hacking ---&gt;
114 x86 Debugging ---&gt;
115 Choose kernel unwinder (Frame pointer unwinder) ---&gt; [CONFIG_UNWINDER_FRAME_POINTER]</screen>
117 </note>
119 <note revision="systemd">
120 <para>While "The IPv6 Protocol" is not strictly
121 required, it is highly recommended by the systemd developers.</para>
122 </note>
124 <para revision="sysv">There are several other options that may be desired
125 depending on the requirements for the system. For a list of options needed
126 for BLFS packages, see the <ulink
127 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
128 Index of Kernel Settings</ulink>
129 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
131 <note>
132 <para>If your host hardware is using UEFI, then the 'make defconfig'
133 above should automatically add in some EFI-related kernel options.</para>
135 <para>In order to allow your LFS kernel to be booted from within your
136 host's UEFI boot environment, your kernel must have this option
137 selected:</para>
139<screen role="nodump">Processor type and features ---&gt;
140 [*] EFI stub support [CONFIG_EFI_STUB]</screen>
142 <para>A fuller description of managing UEFI environments from within LFS
143 is covered by the lfs-uefi.txt hint at
144 <ulink
145 url=""/>.
146 </para>
147 </note>
149 <note arch="ml_32,ml_x32,ml_all">
150 <para>
151 Running a multilib system means also that the kernel has to be
152 configured proper. It is required that the kernel is able to
153 identify and start binaries compiled for different architectures
154 than the default. Setup the required parameter in the kernel
155 config:
156 </para>
157<screen>Binary Emulations ---&gt;
158 [*] IA32 Emulation
159 &lt;M&gt; IA32 a.out support
160 [*] x32 ABI for 64-bit mode
162 <para>Make sure that the option
163 'IA32 Emulation' is set if you built support for the 32bit ABI.
164 If you selected the x32 ABI or built support for both, also select
165 'x32 ABI for 64-bit mode'. The option 'IA32 a.out support' is
166 optional.
167 </para>
168 </note>
170 <variablelist>
171 <title>The rationale for the above configuration items:</title>
173 <varlistentry>
174 <term><parameter>Support for uevent helper</parameter></term>
175 <listitem>
176 <para>Having this option set may interfere with device
177 management when using Udev/Eudev. </para>
178 </listitem>
179 </varlistentry>
181 <varlistentry>
182 <term><parameter>Maintain a devtmpfs</parameter></term>
183 <listitem>
184 <para>This will create automated device nodes which are populated by the
185 kernel, even without Udev running. Udev then runs on top of this,
186 managing permissions and adding symlinks. This configuration
187 item is required for all users of Udev/Eudev.</para>
188 </listitem>
189 </varlistentry>
191 </variablelist>
193<screen role="nodump"><userinput>make menuconfig</userinput></screen>
195 <variablelist>
196 <title>The meaning of optional make environment variables:</title>
198 <varlistentry>
199 <term><parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
200 <listitem>
201 <para>This establishes the locale setting to the one used on the
202 host. This may be needed for a proper menuconfig ncurses interface
203 line drawing on a UTF-8 linux text console.</para>
205 <para>If used, be sure to replace
206 <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
207 the <envar>$LANG</envar> variable from your host. You can
208 alternatively use instead the host's value of <envar>$LC_ALL</envar>
209 or <envar>$LC_CTYPE</envar>.</para>
210 </listitem>
211 </varlistentry>
213 </variablelist>
215 <para>Alternatively, <command>make oldconfig</command> may be more
216 appropriate in some situations. See the <filename>README</filename>
217 file for more information.</para>
219 <para>If desired, skip kernel configuration by copying the kernel
220 config file, <filename>.config</filename>, from the host system
221 (assuming it is available) to the unpacked <filename
222 class="directory">linux-&linux-version;</filename> directory. However,
223 we do not recommend this option. It is often better to explore all the
224 configuration menus and create the kernel configuration from
225 scratch.</para>
227 <para>Compile the kernel image and modules:</para>
229<screen><userinput remap="make">make</userinput></screen>
231 <para>If using kernel modules, module configuration in <filename
232 class="directory">/etc/modprobe.d</filename> may be required.
233 Information pertaining to modules and kernel configuration is
234 located in <xref linkend="ch-config-udev"/> and in the kernel
235 documentation in the <filename
236 class="directory">linux-&linux-version;/Documentation</filename> directory.
237 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
239 <para>Unless module support has been disabled in the kernel configuration,
240 install the modules with:</para>
242<screen><userinput remap="install">make modules_install</userinput></screen>
244 <para>After kernel compilation is complete, additional steps are
245 required to complete the installation. Some files need to be copied to
246 the <filename class="directory">/boot</filename> directory.</para>
248 <caution>
249 <para>If the host system has a separate /boot partition, the files copied
250 below should go there. The easiest way to do that is to bind /boot on the
251 host (outside chroot) to /mnt/lfs/boot before proceeding. As the root
252 user in the <emphasis>host system</emphasis>:</para>
254<screen role="nodump"><userinput>mount --bind /boot /mnt/lfs/boot</userinput></screen>
255 </caution>
257 <para>The path to the kernel image may vary depending on the platform being
258 used. The filename below can be changed to suit your taste, but the stem of
259 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
260 the automatic setup of the boot process described in the next section. The
261 following command assumes an x86 architecture:</para>
263<screen arch="default" revision="sysv"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
265<screen arch="ml_32,ml_x32,ml_all" revision="sysv"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;-multilib</userinput></screen>
267<screen arch="default" revision="systemd"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&versiond;</userinput></screen>
269<screen arch="ml_32,ml_x32,ml_all" revision="systemd"><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&versiond;-multilib</userinput></screen>
272 <para><filename></filename> is a symbol file for the kernel.
273 It maps the function entry points of every function in the kernel API,
274 as well as the addresses of the kernel data structures for the running
275 kernel. It is used as a resource when investigating kernel problems.
276 Issue the following command to install the map file:</para>
278<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
280 <para>The kernel configuration file <filename>.config</filename>
281 produced by the <command>make menuconfig</command> step
282 above contains all the configuration selections for the kernel
283 that was just compiled. It is a good idea to keep this file for future
284 reference:</para>
286<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
288 <para>Install the documentation for the Linux kernel:</para>
290<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
291cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
293 <para>It is important to note that the files in the kernel source
294 directory are not owned by <emphasis>root</emphasis>. Whenever a
295 package is unpacked as user <emphasis>root</emphasis> (like we did
296 inside chroot), the files have the user and group IDs of whatever
297 they were on the packager's computer. This is usually not a problem
298 for any other package to be installed because the source tree is
299 removed after the installation. However, the Linux source tree is
300 often retained for a long time. Because of this, there is a chance
301 that whatever user ID the packager used will be assigned to somebody
302 on the machine. That person would then have write access to the kernel
303 source.</para>
305 <note>
306 <para>In many cases, the configuration of the kernel will need to be
307 updated for packages that will be installed later in BLFS. Unlike
308 other packages, it is not necessary to remove the kernel source tree
309 after the newly built kernel is installed.</para>
311 <para>If the kernel source tree is going to be retained, run
312 <command>chown -R 0:0</command> on the <filename
313 class="directory">linux-&linux-version;</filename> directory to ensure
314 all files are owned by user <emphasis>root</emphasis>.</para>
315 </note>
317 <warning>
318 <para>Some kernel documentation recommends creating a symlink from
319 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
320 source directory. This is specific to kernels prior to the 2.6 series and
321 <emphasis>must not</emphasis> be created on an LFS system as it can cause
322 problems for packages you may wish to build once your base LFS system is
323 complete.</para>
324 </warning>
326 <warning>
327 <para>The headers in the system's <filename
328 class="directory">include</filename> directory (<filename
329 class="directory">/usr/include</filename>) should
330 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
331 that is, the sanitised headers installed in <xref
332 linkend="ch-system-linux-headers"/>. Therefore, they should
333 <emphasis>never</emphasis> be replaced by either the raw kernel headers
334 or any other kernel sanitized headers.</para>
335 </warning>
337 </sect2>
339 <sect2 id="conf-modprobe" role="configuration">
340 <title>Configuring Linux Module Load Order</title>
342 <indexterm zone="conf-modprobe">
343 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
344 </indexterm>
346 <para>Most of the time Linux modules are loaded automatically, but
347 sometimes it needs some specific direction. The program that loads
348 modules, <command>modprobe</command> or <command>insmod</command>, uses
349 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
350 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
351 uhci_hcd) have been built as modules, they will be loaded in the correct
352 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
353 to avoid a warning being output at boot time.</para>
355 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
356 the following:</para>
358<screen><userinput>install -v -m755 -d /etc/modprobe.d
359cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
360<literal># Begin /etc/modprobe.d/usb.conf
362install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
363install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
365# End /etc/modprobe.d/usb.conf</literal>
368 </sect2>
370 <sect2 id="contents-kernel" role="content">
371 <title>Contents of Linux</title>
373 <segmentedlist>
374 <segtitle>Installed files</segtitle>
375 <segtitle>Installed directories</segtitle>
377 <seglistitem>
378 <seg>config-&linux-version;,
379 <phrase arch="default" revision="sysv">vmlinuz-&linux-version;-lfs-&version;,</phrase>
380 <phrase arch="default" revision="systemd">vmlinuz-&linux-version;-lfs-&versiond;,</phrase>
381 <phrase arch="ml_32,ml_x32,ml_all" revision="sysv">vmlinuz-&linux-version;-lfs-&version;-multilib,</phrase>
382 <phrase arch="ml_32,ml_x32,ml_all" revision="systemd">vmlinuz-&linux-version;-lfs-&versiond;-multilib,</phrase>
383 and;</seg>
384 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
385 </seglistitem>
386 </segmentedlist>
388 <variablelist>
389 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
390 <?dbfo list-presentation="list"?>
391 <?dbhtml list-presentation="table"?>
393 <varlistentry id="config">
394 <term><filename>config-&linux-version;</filename></term>
395 <listitem>
396 <para>Contains all the configuration selections for the kernel</para>
397 <indexterm zone="ch-bootable-kernel config">
398 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
399 </indexterm>
400 </listitem>
401 </varlistentry>
403 <varlistentry id="lfskernel">
404 <term revision="sysv"><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
405 <term revision="systemd"><filename>vmlinuz-&linux-version;-lfs-&versiond;</filename></term>
406 <listitem>
407 <para>The engine of the Linux system. When turning on the computer,
408 the kernel is the first part of the operating system that gets loaded.
409 It detects and initializes all components of the computer's hardware,
410 then makes these components available as a tree of files to the
411 software and turns a single CPU into a multitasking machine capable
412 of running scores of programs seemingly at the same time</para>
413 <indexterm zone="ch-bootable-kernel lfskernel">
414 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
415 </indexterm>
416 </listitem>
417 </varlistentry>
419 <varlistentry id="">
420 <term><filename>;</filename></term>
421 <listitem>
422 <para>A list of addresses and symbols; it maps the entry points and
423 addresses of all the functions and data structures in the
424 kernel</para>
425 <indexterm zone="ch-bootable-kernel">
426 <primary sortas="e-/boot/">/boot/;</primary>
427 </indexterm>
428 </listitem>
429 </varlistentry>
431 </variablelist>
433 </sect2>
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