source: chapter10/kernel.xml@ 6c952e3

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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 [*] Support for frame buffer devices ----
121 Generic Driver Options ---&gt;
122 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
123 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
124 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]</screen>
126 <screen role="nodump" revision="systemd">Processor type and features ---&gt;
127 [*] Build a relocatable kernel [CONFIG_RELOCATABLE]
128 [*] Randomize the address of the kernel image (KASLR) [CONFIG_RANDOMIZE_BASE]
129General setup ---&gt;
130 [ ] Compile the kernel with warnings as errors [CONFIG_WERROR]
131 [ ] Auditing Support [CONFIG_AUDIT]
132 CPU/Task time and stats accounting ---&gt;
133 [*] Pressure stall information tracking [CONFIG_PSI]
134 &lt; &gt; Enable kernel headers through /sys/kernel/kheaders.tar.xz [CONFIG_IKHEADERS]
135 [*] Control Group support [CONFIG_CGROUPS] ---&gt;
136 [*] Memory controller [CONFIG_MEMCG]
137 [ ] Enable deprecated sysfs features to support old userspace tools [CONFIG_SYSFS_DEPRECATED]
138 [*] Configure standard kernel features (expert users) [CONFIG_EXPERT] ---&gt;
139 [*] open by fhandle syscalls [CONFIG_FHANDLE]
140General architecture-dependent options ---&gt;
141 [*] Enable seccomp to safely compute untrusted bytecode [CONFIG_SECCOMP]
142 [*] Stack Protector buffer overflow detection [CONFIG_STACKPROTECTOR]
143 [*] Strong Stack Protector [CONFIG_STACKPROTECTOR_STRONG]
144Networking support ---&gt;
145 Networking options ---&gt;
146 &lt;*&gt; The IPv6 protocol [CONFIG_IPV6]
147Device Drivers ---&gt;
148 Generic Driver Options ---&gt;
149 [ ] Support for uevent helper [CONFIG_UEVENT_HELPER]
150 [*] Maintain a devtmpfs filesystem to mount at /dev [CONFIG_DEVTMPFS]
151 [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs [CONFIG_DEVTMPFS_MOUNT]
152 Firmware Loader ---&gt;
153 [ ] Enable the firmware sysfs fallback mechanism [CONFIG_FW_LOADER_USER_HELPER]
154 Firmware Drivers ---&gt;
155 [*] Export DMI identification via sysfs to userspace [CONFIG_DMIID]
156 Graphics support ---&gt;
157 Frame buffer Devices ---&gt;
158 &lt;*&gt; Support for frame buffer devices ---&gt;
159File systems ---&gt;
160 [*] Inotify support for userspace [CONFIG_INOTIFY_USER]
161 Pseudo filesystems ---&gt;
162 [*] Tmpfs POSIX Access Control Lists [CONFIG_TMPFS_POSIX_ACL]</screen>
164 <para>Enable some additional features if you are building a 64-bit
165 system. If you are using menuconfig, enable them in the order of
166 <parameter>CONFIG_PCI_MSI</parameter> first, then
167 <parameter>CONFIG_IRQ_REMAP</parameter>, at last
168 <parameter>CONFIG_X86_X2APIC</parameter> because an option only
169 shows up after its dependencies are selected.</para>
171 <screen role="nodump">Processor type and features ---&gt;
172 [*] Support x2apic [CONFIG_X86_X2APIC]
173Device Drivers ---&gt;
174 [*] PCI Support ---&gt; [CONFIG_PCI]
175 [*] Message Signaled Interrupts (MSI and MSI-X) [CONFIG_PCI_MSI]
176 [*] IOMMU Hardware Support ---&gt; [CONFIG_IOMMU_SUPPORT]
177 [*] Support for Interrupt Remapping [CONFIG_IRQ_REMAP]</screen>
178 </note>
180 <note revision="systemd">
181 <para>While "The IPv6 Protocol" is not strictly
182 required, it is highly recommended by the systemd developers.</para>
183 </note>
185 <para revision="sysv">There are several other options that may be desired
186 depending on the requirements for the system. For a list of options needed
187 for BLFS packages, see the <ulink
188 url="&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index">BLFS
189 Index of Kernel Settings</ulink>
190 (&lfs-root;blfs/view/&short-version;/longindex.html#kernel-config-index).</para>
192 <note>
193 <para>If your host hardware is using UEFI and you wish to boot the
194 LFS system with it, you should adjust some kernel configuration
195 following <ulink url="&blfs-book;postlfs/grub-setup.html#uefi-kernel">
196 the BLFS page</ulink>.</para>
197 </note>
199 <variablelist>
200 <title>The rationale for the above configuration items:</title>
202 <varlistentry>
203 <term><parameter>Randomize the address of the kernel image (KASLR)</parameter></term>
204 <listitem>
205 <para>Enable ASLR for kernel image, to mitigate some attacks based
206 on fixed addresses of sensitive data or code in the kernel.</para>
207 </listitem>
208 </varlistentry>
210 <varlistentry>
211 <term>
212 <parameter>
213 Compile the kernel with warnings as errors
214 </parameter>
215 </term>
216 <listitem>
217 <para>This may cause building failure if the compiler and/or
218 configuration are different from those of the kernel
219 developers.</para>
220 </listitem>
221 </varlistentry>
223 <varlistentry>
224 <term>
225 <parameter>
226 Enable kernel headers through /sys/kernel/kheaders.tar.xz
227 </parameter>
228 </term>
229 <listitem>
230 <para>This will require <command>cpio</command> building the kernel.
231 <command>cpio</command> is not installed by LFS.</para>
232 </listitem>
233 </varlistentry>
235 <varlistentry>
236 <term><parameter>Strong Stack Protector</parameter></term>
237 <listitem>
238 <para>Enable SSP for the kernel. We've enabled it for the entire
239 userspace with <parameter>--enable-default-ssp</parameter>
240 configuring GCC, but the kernel does not use GCC default setting
241 for SSP. We enable it explicitly here.</para>
242 </listitem>
243 </varlistentry>
245 <varlistentry>
246 <term><parameter>Support for uevent helper</parameter></term>
247 <listitem>
248 <para>Having this option set may interfere with device
249 management when using Udev/Eudev. </para>
250 </listitem>
251 </varlistentry>
253 <varlistentry>
254 <term><parameter>Maintain a devtmpfs</parameter></term>
255 <listitem>
256 <para>This will create automated device nodes which are populated by the
257 kernel, even without Udev running. Udev then runs on top of this,
258 managing permissions and adding symlinks. This configuration
259 item is required for all users of Udev/Eudev.</para>
260 </listitem>
261 </varlistentry>
263 <varlistentry>
264 <term><parameter>Automount devtmpfs at /dev</parameter></term>
265 <listitem>
266 <para>This will mount the kernel view of the devices on /dev
267 upon switching to root filesystem just before starting
268 init.</para>
269 </listitem>
270 </varlistentry>
272 <varlistentry>
273 <term><parameter>Support x2apic</parameter></term>
274 <listitem>
275 <para>Support running the interrupt controller of 64-bit x86
276 processors in x2APIC mode. x2APIC may be enabled by firmware on
277 64-bit x86 systems, and a kernel without this option enabled will
278 panic on boot if x2APIC is enabled by firmware. This option has
279 has no effect, but also does no harm if x2APIC is disabled by the
280 firmware.</para>
281 </listitem>
282 </varlistentry>
284 </variablelist>
286 <para>Alternatively, <command>make oldconfig</command> may be more
287 appropriate in some situations. See the <filename>README</filename>
288 file for more information.</para>
290 <para>If desired, skip kernel configuration by copying the kernel
291 config file, <filename>.config</filename>, from the host system
292 (assuming it is available) to the unpacked <filename
293 class="directory">linux-&linux-version;</filename> directory. However,
294 we do not recommend this option. It is often better to explore all the
295 configuration menus and create the kernel configuration from
296 scratch.</para>
298 <para>Compile the kernel image and modules:</para>
300<screen><userinput remap="make">make</userinput></screen>
302 <para>If using kernel modules, module configuration in <filename
303 class="directory">/etc/modprobe.d</filename> may be required.
304 Information pertaining to modules and kernel configuration is
305 located in <xref linkend="ch-config-udev"/> and in the kernel
306 documentation in the <filename
307 class="directory">linux-&linux-version;/Documentation</filename> directory.
308 Also, <filename>modprobe.d(5)</filename> may be of interest.</para>
310 <para>Unless module support has been disabled in the kernel configuration,
311 install the modules with:</para>
313<screen><userinput remap="install">make modules_install</userinput></screen>
315 <para>After kernel compilation is complete, additional steps are
316 required to complete the installation. Some files need to be copied to
317 the <filename class="directory">/boot</filename> directory.</para>
319 <caution>
320 <para>As the cross-built LFS system has a separate /boot partition,
321 the files copied below should go there. The easiest way to do that is
322 to mount <filename class="directory">/boot</filename> before
323 proceeding. As the &root; user:</para>
325<screen role="nodump"><userinput>mount /boot</userinput></screen>
327 <para>We don't need to specify the path to the device node, as it's
328 already given in <filename>/etc/fstab</filename>.</para>
329 </caution>
331 <para>The path to the kernel image may vary depending on the platform being
332 used. The filename below can be changed to suit your taste, but the stem of
333 the filename should be <emphasis>vmlinuz</emphasis> to be compatible with
334 the automatic setup of the boot process described in the next section. The
335 following command assumes an x86 architecture:</para>
337<screen><userinput remap="install">cp -iv arch/x86/boot/bzImage /boot/vmlinuz-&linux-version;-lfs-&version;</userinput></screen>
339 <para><filename></filename> is a symbol file for the kernel.
340 It maps the function entry points of every function in the kernel API,
341 as well as the addresses of the kernel data structures for the running
342 kernel. It is used as a resource when investigating kernel problems.
343 Issue the following command to install the map file:</para>
345<screen><userinput remap="install">cp -iv /boot/;</userinput></screen>
347 <para>The kernel configuration file <filename>.config</filename>
348 produced by the <command>make menuconfig</command> step
349 above contains all the configuration selections for the kernel
350 that was just compiled. It is a good idea to keep this file for future
351 reference:</para>
353<screen><userinput remap="install">cp -iv .config /boot/config-&linux-version;</userinput></screen>
355 <para>Install the documentation for the Linux kernel:</para>
357<screen><userinput remap="install">install -d /usr/share/doc/linux-&linux-version;
358cp -r Documentation/* /usr/share/doc/linux-&linux-version;</userinput></screen>
360 <para>It is important to note that the files in the kernel source
361 directory are not owned by <emphasis>root</emphasis>. Whenever a
362 package is unpacked as user <emphasis>root</emphasis> (like we did
363 inside chroot), the files have the user and group IDs of whatever
364 they were on the packager's computer. This is usually not a problem
365 for any other package to be installed because the source tree is
366 removed after the installation. However, the Linux source tree is
367 often retained for a long time. Because of this, there is a chance
368 that whatever user ID the packager used will be assigned to somebody
369 on the machine. That person would then have write access to the kernel
370 source.</para>
372 <note>
373 <para>In many cases, the configuration of the kernel will need to be
374 updated for packages that will be installed later in BLFS. Unlike
375 other packages, it is not necessary to remove the kernel source tree
376 after the newly built kernel is installed.</para>
378 <para>If the kernel source tree is going to be retained, run
379 <command>chown -R 0:0</command> on the <filename
380 class="directory">linux-&linux-version;</filename> directory to ensure
381 all files are owned by user <emphasis>root</emphasis>.</para>
382 </note>
384 <warning>
385 <para>Some kernel documentation recommends creating a symlink from
386 <filename class="symlink">/usr/src/linux</filename> pointing to the kernel
387 source directory. This is specific to kernels prior to the 2.6 series and
388 <emphasis>must not</emphasis> be created on an LFS system as it can cause
389 problems for packages you may wish to build once your base LFS system is
390 complete.</para>
391 </warning>
393 <warning>
394 <para>The headers in the system's <filename
395 class="directory">include</filename> directory (<filename
396 class="directory">/usr/include</filename>) should
397 <emphasis>always</emphasis> be the ones against which Glibc was compiled,
398 that is, the sanitised headers installed in <xref
399 linkend="ch-tools-linux-headers"/>. Therefore, they should
400 <emphasis>never</emphasis> be replaced by either the raw kernel headers
401 or any other kernel sanitized headers.</para>
402 </warning>
404 </sect2>
406 <sect2 id="conf-modprobe" role="configuration">
407 <title>Configuring Linux Module Load Order</title>
409 <indexterm zone="conf-modprobe">
410 <primary sortas="e-/etc/modprobe.d/usb.conf">/etc/modprobe.d/usb.conf</primary>
411 </indexterm>
413 <para>Most of the time Linux modules are loaded automatically, but
414 sometimes it needs some specific direction. The program that loads
415 modules, <command>modprobe</command> or <command>insmod</command>, uses
416 <filename>/etc/modprobe.d/usb.conf</filename> for this purpose. This file
417 needs to be created so that if the USB drivers (ehci_hcd, ohci_hcd and
418 uhci_hcd) have been built as modules, they will be loaded in the correct
419 order; ehci_hcd needs to be loaded prior to ohci_hcd and uhci_hcd in order
420 to avoid a warning being output at boot time.</para>
422 <para>Create a new file <filename>/etc/modprobe.d/usb.conf</filename> by running
423 the following:</para>
425<screen><userinput>install -v -m755 -d /etc/modprobe.d
426cat &gt; /etc/modprobe.d/usb.conf &lt;&lt; "EOF"
427<literal># Begin /etc/modprobe.d/usb.conf
429install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
430install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true
432# End /etc/modprobe.d/usb.conf</literal>
435 </sect2>
437 <sect2 id="contents-kernel" role="content">
438 <title>Contents of Linux</title>
440 <segmentedlist>
441 <segtitle>Installed files</segtitle>
442 <segtitle>Installed directories</segtitle>
444 <seglistitem>
445 <seg>config-&linux-version;,
446 vmlinuz-&linux-version;-lfs-&version;,
447 and;</seg>
448 <seg>/lib/modules, /usr/share/doc/linux-&linux-version;</seg>
449 </seglistitem>
450 </segmentedlist>
452 <variablelist>
453 <bridgehead renderas="sect3">Short Descriptions</bridgehead>
454 <?dbfo list-presentation="list"?>
455 <?dbhtml list-presentation="table"?>
457 <varlistentry id="config">
458 <term><filename>config-&linux-version;</filename></term>
459 <listitem>
460 <para>Contains all the configuration selections for the kernel</para>
461 <indexterm zone="ch-bootable-kernel config">
462 <primary sortas="e-/boot/config">/boot/config-&linux-version;</primary>
463 </indexterm>
464 </listitem>
465 </varlistentry>
467 <varlistentry id="lfskernel">
468 <term><filename>vmlinuz-&linux-version;-lfs-&version;</filename></term>
469 <listitem>
470 <para>The engine of the Linux system. When turning on the computer,
471 the kernel is the first part of the operating system that gets loaded.
472 It detects and initializes all components of the computer's hardware,
473 then makes these components available as a tree of files to the
474 software and turns a single CPU into a multitasking machine capable
475 of running scores of programs seemingly at the same time</para>
476 <indexterm zone="ch-bootable-kernel lfskernel">
477 <primary sortas="b-lfskernel">lfskernel-&linux-version;</primary>
478 </indexterm>
479 </listitem>
480 </varlistentry>
482 <varlistentry id="">
483 <term><filename>;</filename></term>
484 <listitem>
485 <para>A list of addresses and symbols; it maps the entry points and
486 addresses of all the functions and data structures in the
487 kernel</para>
488 <indexterm zone="ch-bootable-kernel">
489 <primary sortas="e-/boot/">/boot/;</primary>
490 </indexterm>
491 </listitem>
492 </varlistentry>
494 </variablelist>
496 </sect2>
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