source: chapter10/kernel.xml@ 0ea3431

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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-knl-sbu;</seg>
34 <seg>&linux-knl-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 <para>There are several ways to configure the kernel options. Usually,
58 This is done through a menu-driven interface, for example:</para>
60<screen role="nodump"><userinput>make menuconfig</userinput></screen>
62 <variablelist>
63 <title>The meaning of optional make environment variables:</title>
65 <varlistentry>
66 <term><parameter>LANG=&lt;host_LANG_value&gt; LC_ALL=</parameter></term>
67 <listitem>
68 <para>This establishes the locale setting to the one used on the
69 host. This may be needed for a proper menuconfig ncurses interface
70 line drawing on a UTF-8 linux text console.</para>
72 <para>If used, be sure to replace
73 <replaceable>&lt;host_LANG_value&gt;</replaceable> by the value of
74 the <envar>$LANG</envar> variable from your host. You can
75 alternatively use instead the host's value of <envar>$LC_ALL</envar>
76 or <envar>$LC_CTYPE</envar>.</para>
77 </listitem>
78 </varlistentry>
80 <varlistentry>
81 <term><command>make menuconfig</command></term>
82 <listitem>
83 <para>This launches an ncurses menu-driven interface. For other
84 (graphical) interfaces, type <command>make help</command>.</para>
85 </listitem>
86 </varlistentry>
87 </variablelist>
89 <!-- Support for compiling a keymap into the kernel is deliberately removed -->
91 <para>For general information on kernel configuration see <ulink
92 url="&hints-root;kernel-configuration.txt"/>. BLFS has some information
93 regarding particular kernel configuration requirements of packages outside
94 of LFS at <ulink
95 url="&blfs-book;longindex.html#kernel-config-index"/>. Additional
96 information about configuring and building the kernel can be found at
97 <ulink url=""/> </para>
99 <note>
100 <para>A good starting place for setting up the kernel configuration is to
101 run <command>make defconfig</command>. This will set the base
102 configuration to a good state that takes your current system architecture
103 into account.</para>
105 <para>Be sure to enable/disable/set the following features or the system might
106 not work correctly or boot at all:</para>
108 <screen role="nodump" revision="sysv">Processor type and features ---&gt;
109 [*] Build a relocatable kernel [CONFIG_RELOCATABLE]
110 [*] Randomize the address of the kernel image (KASLR) [CONFIG_RANDOMIZE_BASE]
111General setup ---&gt;
112 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
113 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
114General architecture-dependent options ---&gt;
115 [*] Stack Protector buffer overflow detection [CONFIG_STACKPROTECTOR]
116 [*] Strong Stack Protector [CONFIG_STACKPROTECTOR_STRONG]
117Device Drivers ---&gt;
118 Graphics support ---&gt;
119 Frame buffer Devices ---&gt;
120 &lt;*&gt; Support for frame buffer devices ---&gt;
121 Console display driver support ---&gt;
122 [*] Framebuffer Console support [CONFIG_FRAMEBUFFER_CONSOLE]
123 Generic Driver Options ---&gt;
124 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
125 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
126 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]</screen>
128 <screen role="nodump" revision="systemd">Processor type and features ---&gt;
129 [*] Build a relocatable kernel [CONFIG_RELOCATABLE]
130 [*] Randomize the address of the kernel image (KASLR) [CONFIG_RANDOMIZE_BASE]
131General setup ---&gt;
132 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
133 [ ] Auditing Support [CONFIG_AUDIT]
134 CPU/Task time and stats accounting ---&gt;
135 [*] Pressure stall information tracking [CONFIG_PSI]
136 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
137 [*] Control Group support [CONFIG_CGROUPS] ---&gt;
138 [*] Memory controller [CONFIG_MEMCG]
139 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
140 [*] Configure standard kernel features (expert users) [CONFIG_EXPERT] ---&gt;
141 [*] open by fhandle syscalls [CONFIG_FHANDLE]
142General architecture-dependent options ---&gt;
143 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
144 [*] Stack Protector buffer overflow detection [CONFIG_STACKPROTECTOR]
145 [*] Strong Stack Protector [CONFIG_STACKPROTECTOR_STRONG]
146Networking support ---&gt;
147 Networking options ---&gt;
148 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
149Device Drivers ---&gt;
150 Generic Driver Options ---&gt;
151 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
152 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
153 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]
154 Firmware Loader ---&gt;
155 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
156 Firmware Drivers ---&gt;
157 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
158 Graphics support ---&gt;
159 Frame buffer Devices ---&gt;
160 &lt;*&gt; Support for frame buffer devices ---&gt;
161 Console display driver support ---&gt;
162 [*] Framebuffer Console support [CONFIG_FRAMEBUFFER_CONSOLE]
163File systems ---&gt;
164 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
165 Pseudo filesystems ---&gt;
166 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]</screen>
168 <para>Enable some additional features if you are building a 64-bit
169 system. If you are using menuconfig, enable them in the order of
170 <parameter>CONFIG_PCI_MSI</parameter> first, then
171 <parameter>CONFIG_IRQ_REMAP</parameter>, at last
172 <parameter>CONFIG_X86_X2APIC</parameter> because an option only
173 shows up after its dependencies are selected.</para>
175 <screen role="nodump">Processor type and features ---&gt;
176 [*] Support x2apic [CONFIG_X86_X2APIC]
177Device Drivers ---&gt;
178 [*] PCI Support ---&gt; [CONFIG_PCI]
179 [*] Message Signaled Interrupts (MSI and MSI-X) [CONFIG_PCI_MSI]
180 [*] IOMMU Hardware Support ---&gt; [CONFIG_IOMMU_SUPPORT]
181 [*] Support for Interrupt Remapping [CONFIG_IRQ_REMAP]</screen>
182 </note>
184 <note revision="systemd">
185 <para>While "The IPv6 Protocol" is not strictly
186 required, it is highly recommended by the systemd developers.</para>
187 </note>
189 <para revision="sysv">There are several other options that may be desired
190 depending on the requirements for the system. For a list of options needed
191 for BLFS packages, see the <ulink
192 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
193 Index of Kernel Settings</ulink>
194 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
196 <note>
197 <para>If your host hardware is using UEFI and you wish to boot the
198 LFS system with it, you should adjust some kernel configuration
199 following <ulink url="&blfs-book;postlfs/grub-setup.html#uefi-kernel">
200 the BLFS page</ulink>.</para>
201 </note>
203 <variablelist>
204 <title>The rationale for the above configuration items:</title>
206 <varlistentry>
207 <term><parameter>Randomize the address of the kernel image (KASLR)</parameter></term>
208 <listitem>
209 <para>Enable ASLR for kernel image, to mitigate some attacks based
210 on fixed addresses of sensitive data or code in the kernel.</para>
211 </listitem>
212 </varlistentry>
214 <varlistentry>
215 <term>
216 <parameter>
217 Compile the kernel with warnings as errors
218 </parameter>
219 </term>
220 <listitem>
221 <para>This may cause building failure if the compiler and/or
222 configuration are different from those of the kernel
223 developers.</para>
224 </listitem>
225 </varlistentry>
227 <varlistentry>
228 <term>
229 <parameter>
230 Enable kernel headers through /sys/kernel/kheaders.tar.xz
231 </parameter>
232 </term>
233 <listitem>
234 <para>This will require <command>cpio</command> building the kernel.
235 <command>cpio</command> is not installed by LFS.</para>
236 </listitem>
237 </varlistentry>
239 <varlistentry>
240 <term><parameter>Strong Stack Protector</parameter></term>
241 <listitem>
242 <para>Enable SSP for the kernel. We've enabled it for the entire
243 userspace with <parameter>--enable-default-ssp</parameter>
244 configuring GCC, but the kernel does not use GCC default setting
245 for SSP. We enable it explicitly here.</para>
246 </listitem>
247 </varlistentry>
249 <varlistentry>
250 <term><parameter>Support for uevent helper</parameter></term>
251 <listitem>
252 <para>Having this option set may interfere with device
253 management when using Udev/Eudev. </para>
254 </listitem>
255 </varlistentry>
257 <varlistentry>
258 <term><parameter>Maintain a devtmpfs</parameter></term>
259 <listitem>
260 <para>This will create automated device nodes which are populated by the
261 kernel, even without Udev running. Udev then runs on top of this,
262 managing permissions and adding symlinks. This configuration
263 item is required for all users of Udev/Eudev.</para>
264 </listitem>
265 </varlistentry>
267 <varlistentry>
268 <term><parameter>Automount devtmpfs at /dev</parameter></term>
269 <listitem>
270 <para>This will mount the kernel view of the devices on /dev
271 upon switching to root filesystem just before starting
272 init.</para>
273 </listitem>
274 </varlistentry>
276 <varlistentry>
277 <term><parameter>Framebuffer Console support</parameter></term>
278 <listitem>
279 <para>This is needed to display the Linux console on a frame
280 buffer device. To allow the kernel to print debug messages at an
281 early boot stage, it shouldn't be built as a kernel module
282 unless an initramfs will be used. And, if
283 <option>CONFIG_DRM</option> (Direct Rendering Manager) is enabled,
284 it's likely <option>CONFIG_DRM_FBDEV_EMULATION</option> (Enable
285 legacy fbdev support for your modesetting driver) should be
286 enabled as well.</para>
287 </listitem>
288 </varlistentry>
290 <varlistentry>
291 <term><parameter>Support x2apic</parameter></term>
292 <listitem>
293 <para>Support running the interrupt controller of 64-bit x86
294 processors in x2APIC mode. x2APIC may be enabled by firmware on
295 64-bit x86 systems, and a kernel without this option enabled will
296 panic on boot if x2APIC is enabled by firmware. This option has
297 has no effect, but also does no harm if x2APIC is disabled by the
298 firmware.</para>
299 </listitem>
300 </varlistentry>
302 </variablelist>
304 <para>Alternatively, <command>make oldconfig</command> may be more
305 appropriate in some situations. See the <filename>README</filename>
306 file for more information.</para>
308 <para>If desired, skip kernel configuration by copying the kernel
309 config file, <filename>.config</filename>, from the host system
310 (assuming it is available) to the unpacked <filename
311 class="directory">linux-&linux-version;</filename> directory. However,
312 we do not recommend this option. It is often better to explore all the
313 configuration menus and create the kernel configuration from
314 scratch.</para>
316 <para>Compile the kernel image and modules:</para>
318<screen><userinput remap="make">make</userinput></screen>
320 <para>If using kernel modules, module configuration in <filename
321 class="directory">/etc/modprobe.d</filename> may be required.
322 Information pertaining to modules and kernel configuration is
323 located in <xref linkend="ch-config-udev"/> and in the kernel
324 documentation in the <filename
325 class="directory">linux-&linux-version;/Documentation</filename> directory.
326 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
328 <para>Unless module support has been disabled in the kernel configuration,
329 install the modules with:</para>
331<screen><userinput remap="install">make modules_install</userinput></screen>
333 <para>After kernel compilation is complete, additional steps are
334 required to complete the installation. Some files need to be copied to
335 the <filename class="directory">/boot</filename> directory.</para>
337 <caution>
338 <para>As the cross-built LFS system has a separate &boot-dir;
339 partition, the files copied below should go there. The easiest way to
340 do that is to create the entry for &boot-dir; in &fstab; first (read
341 the previous section for details), then issue the following command
342 as the &root; user:</para>
344<screen role="nodump"><userinput>mount /boot</userinput></screen>
346 <para>We don't need to specify the path to the device node, as it's
347 already given in <filename>/etc/fstab</filename>.</para>
348 </caution>
350 <para>The path to the kernel image may vary depending on the platform being
351 used. The filename below can be changed to suit your taste, but the stem of
352 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
353 the automatic setup of the boot process described in the next section. The
354 following command assumes an x86 architecture:</para>
356<screen><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
358 <para><filename></filename> is a symbol file for the kernel.
359 It maps the function entry points of every function in the kernel API,
360 as well as the addresses of the kernel data structures for the running
361 kernel. It is used as a resource when investigating kernel problems.
362 Issue the following command to install the map file:</para>
364<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
366 <para>The kernel configuration file <filename>.config</filename>
367 produced by the <command>make menuconfig</command> step
368 above contains all the configuration selections for the kernel
369 that was just compiled. It is a good idea to keep this file for future
370 reference:</para>
372<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
374 <para>Install the documentation for the Linux kernel:</para>
376<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
377cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
379 <para>It is important to note that the files in the kernel source
380 directory are not owned by <emphasis>root</emphasis>. Whenever a
381 package is unpacked as user <emphasis>root</emphasis> (like we did
382 inside chroot), the files have the user and group IDs of whatever
383 they were on the packager's computer. This is usually not a problem
384 for any other package to be installed because the source tree is
385 removed after the installation. However, the Linux source tree is
386 often retained for a long time. Because of this, there is a chance
387 that whatever user ID the packager used will be assigned to somebody
388 on the machine. That person would then have write access to the kernel
389 source.</para>
391 <note>
392 <para>In many cases, the configuration of the kernel will need to be
393 updated for packages that will be installed later in BLFS. Unlike
394 other packages, it is not necessary to remove the kernel source tree
395 after the newly built kernel is installed.</para>
397 <para>If the kernel source tree is going to be retained, run
398 <command>chown -R 0:0</command> on the <filename
399 class="directory">linux-&linux-version;</filename> directory to ensure
400 all files are owned by user <emphasis>root</emphasis>.</para>
401 </note>
403 <warning>
404 <para>Some kernel documentation recommends creating a symlink from
405 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
406 source directory. This is specific to kernels prior to the 2.6 series and
407 <emphasis>must not</emphasis> be created on an LFS system as it can cause
408 problems for packages you may wish to build once your base LFS system is
409 complete.</para>
410 </warning>
412 <warning>
413 <para>The headers in the system's <filename
414 class="directory">include</filename> directory (<filename
415 class="directory">/usr/include</filename>) should
416 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
417 that is, the sanitised headers installed in <xref
418 linkend="ch-tools-linux-headers"/>. Therefore, they should
419 <emphasis>never</emphasis> be replaced by either the raw kernel headers
420 or any other kernel sanitized headers.</para>
421 </warning>
423 </sect2>
425 <sect2 id="conf-modprobe" role="configuration">
426 <title>Configuring Linux Module Load Order</title>
428 <indexterm zone="conf-modprobe">
429 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
430 </indexterm>
432 <para>Most of the time Linux modules are loaded automatically, but
433 sometimes it needs some specific direction. The program that loads
434 modules, <command>modprobe</command> or <command>insmod</command>, uses
435 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
436 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
437 uhci_hcd) have been built as modules, they will be loaded in the correct
438 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
439 to avoid a warning being output at boot time.</para>
441 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
442 the following:</para>
444<screen><userinput>install -v -m755 -d /etc/modprobe.d
445cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
446<literal># Begin /etc/modprobe.d/usb.conf
448install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
449install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
451# End /etc/modprobe.d/usb.conf</literal>
454 </sect2>
456 <sect2 id="contents-kernel" role="content">
457 <title>Contents of Linux</title>
459 <segmentedlist>
460 <segtitle>Installed files</segtitle>
461 <segtitle>Installed directories</segtitle>
463 <seglistitem>
464 <seg>config-&linux-version;,
465 vmlinuz-&linux-version;-lfs-&version;,
466 and;</seg>
467 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
468 </seglistitem>
469 </segmentedlist>
471 <variablelist>
472 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
473 <?dbfo list-presentation="list"?>
474 <?dbhtml list-presentation="table"?>
476 <varlistentry id="config">
477 <term><filename>config-&linux-version;</filename></term>
478 <listitem>
479 <para>Contains all the configuration selections for the kernel</para>
480 <indexterm zone="ch-bootable-kernel config">
481 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
482 </indexterm>
483 </listitem>
484 </varlistentry>
486 <varlistentry id="lfskernel">
487 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
488 <listitem>
489 <para>The engine of the Linux system. When turning on the computer,
490 the kernel is the first part of the operating system that gets loaded.
491 It detects and initializes all components of the computer's hardware,
492 then makes these components available as a tree of files to the
493 software and turns a single CPU into a multitasking machine capable
494 of running scores of programs seemingly at the same time</para>
495 <indexterm zone="ch-bootable-kernel lfskernel">
496 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
497 </indexterm>
498 </listitem>
499 </varlistentry>
501 <varlistentry id="">
502 <term><filename>;</filename></term>
503 <listitem>
504 <para>A list of addresses and symbols; it maps the entry points and
505 addresses of all the functions and data structures in the
506 kernel</para>
507 <indexterm zone="ch-bootable-kernel">
508 <primary sortas="e-/boot/">/boot/;</primary>
509 </indexterm>
510 </listitem>
511 </varlistentry>
513 </variablelist>
515 </sect2>
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