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1 <?xml version='1.0' encoding='UTF-8'?>
2 <!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
4 <!-- The content of this document is licensed under the CC-BY-SA license -->
5 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
6
7 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-install-x86+amd64-kernel.xml,v 1.57 2014/08/07 16:15:41 swift Exp $ -->
8
9 <sections>
10
11 <abstract>
12 The Linux kernel is the core of every distribution. This chapter
13 explains how to configure your kernel.
14 </abstract>
15
16 <version>27</version>
17 <date>2014-08-07</date>
18
19 <section>
20 <title>Installing the Sources</title>
21 <subsection>
22 <title>Choosing a Kernel</title>
23 <body>
24
25 <p>
26 The core around which all distributions are built is the Linux kernel. It is the
27 layer between the user programs and your system hardware. Gentoo provides its
28 users several possible kernel sources. A full listing with description is
29 available at the <uri link="https://wiki.gentoo.org/wiki/Kernel/Overview">Gentoo Kernel
30 Guide</uri>.
31 </p>
32
33 <p>
34 For <keyval id="arch"/>-based systems we have <c>gentoo-sources</c>
35 (kernel source patched for extra features).
36 </p>
37
38 <p>
39 Choose your kernel source and install it using <c>emerge</c>.
40 </p>
41
42 <pre caption="Installing a kernel source">
43 # <i>emerge gentoo-sources</i>
44 </pre>
45
46 <p>
47 When you take a look in <path>/usr/src</path> you should see a symlink called
48 <path>linux</path> pointing to your kernel source. In this case, the installed
49 kernel source points to <c>gentoo-sources-<keyval id="kernel-version"/></c>.
50 Your version may be different, so keep this in mind.
51 </p>
52
53 <pre caption="Viewing the kernel source symlink">
54 # <i>ls -l /usr/src/linux</i>
55 lrwxrwxrwx 1 root root 12 Oct 13 11:04 /usr/src/linux -&gt; linux-<keyval id="kernel-version"/>
56 </pre>
57
58 <p>
59 Now it is time to configure and compile your kernel source. You can use
60 <c>genkernel</c> for this, which will build a generic kernel as used by the
61 Installation CD. We explain the "manual" configuration first though, as it is
62 the best way to optimize your environment.
63 </p>
64
65 <p>
66 If you want to manually configure your kernel, continue now with <uri
67 link="#manual">Default: Manual Configuration</uri>. If you want to use
68 <c>genkernel</c> you should read <uri link="#genkernel">Alternative: Using
69 genkernel</uri> instead.
70 </p>
71
72 </body>
73 </subsection>
74 </section>
75 <section id="manual">
76 <title>Default: Manual Configuration</title>
77 <subsection>
78 <title>Introduction</title>
79 <body>
80
81 <p>
82 Manually configuring a kernel is often seen as the most difficult procedure a
83 Linux user ever has to perform. Nothing is less true -- after configuring a
84 couple of kernels you don't even remember that it was difficult ;)
85 </p>
86
87 <p>
88 However, one thing <e>is</e> true: you must know your system when you start
89 configuring a kernel manually. Most information can be gathered by emerging
90 pciutils (<c>emerge pciutils</c>) which contains <c>lspci</c>. You will now
91 be able to use <c>lspci</c> within the chrooted environment. You may safely
92 ignore any <e>pcilib</e> warnings (like pcilib: cannot open
93 /sys/bus/pci/devices) that <c>lspci</c> throws out. Alternatively, you can run
94 <c>lspci</c> from a <e>non-chrooted</e> environment. The results are the same.
95 You can also run <c>lsmod</c> to see what kernel modules the Installation CD
96 uses (it might provide you with a nice hint on what to enable).
97 </p>
98
99 <p>
100 Now go to your kernel source directory and execute <c>make menuconfig</c>. This
101 will fire up an ncurses-based configuration menu.
102 </p>
103
104 <pre caption="Invoking menuconfig">
105 # <i>cd /usr/src/linux</i>
106 # <i>make menuconfig</i>
107 </pre>
108
109 <p>
110 You will be greeted with several configuration sections. We'll first list some
111 options you must activate (otherwise Gentoo will not function, or not function
112 properly without additional tweaks). We also have a <uri
113 link="https://wiki.gentoo.org/wiki/Kernel/Gentoo_Kernel_Configuration_Guide">Gentoo
114 Kernel Configuration Guide</uri> on the Gentoo wiki that might help you further.
115 </p>
116
117 </body>
118 </subsection>
119 <subsection>
120 <title>Activating Required Options</title>
121 <body>
122
123 <p>
124 Make sure that every driver that is vital to the booting of your system (such as
125 SCSI controller, ...) is compiled <e>in</e> the kernel and not as a module,
126 otherwise your system will not be able to boot completely.
127 </p>
128
129 </body>
130 <body test="func:keyval('arch')='AMD64'">
131
132 <p>
133 We shall then select the exact processor type. The x86_64 kernel maintainer
134 strongly recommends users enable MCE features so that they are able to be
135 notified of any hardware problems. On x86_64, these errors are not printed to
136 <c>dmesg</c> like on other architectures, but to <path>/dev/mcelog</path>. This
137 requires the <c>app-admin/mcelog</c> package. Make sure you select IA32
138 Emulation if you want to be able to run 32-bit programs. Gentoo will install a
139 multilib system (mixed 32-bit/64-bit computing) by default, so this option is
140 required.
141 </p>
142
143 <note>
144 If you plan to use a non-multilib profile (for a pure 64-bit system), then you
145 don't have to select IA32 Emulation support. However, you'll also need to follow
146 the <uri link="?part=1&amp;chap=6#doc_chap2_sect4">instructions</uri> for
147 switching to a <uri link="https://wiki.gentoo.org/wiki/AMD64/FAQ">non-multilib
148 profile</uri>, as well as choosing the correct <uri
149 link="?part=1&amp;chap=10#doc_chap2_sect2">bootloader</uri>.
150 </note>
151
152 <pre caption="Selecting processor type and features">
153 Processor type and features --->
154 [ ] Machine Check / overheating reporting
155 [ ] Intel MCE Features
156 [ ] AMD MCE Features
157 Processor family (AMD-Opteron/Athlon64) --->
158 ( ) Opteron/Athlon64/Hammer/K8
159 ( ) Intel P4 / older Netburst based Xeon
160 ( ) Core 2/newer Xeon
161 ( ) Intel Atom
162 ( ) Generic-x86-64
163 Executable file formats / Emulations --->
164 [*] IA32 Emulation
165 </pre>
166
167 </body>
168 <body test="func:keyval('arch')='x86'">
169
170 <p>
171 Now select the correct processor family:
172 </p>
173
174 <pre caption="Selecting correct processor family">
175 Processor type and features ---&gt;
176 <comment>(Change according to your system)</comment>
177 (<i>Athlon/Duron/K7</i>) Processor family
178 </pre>
179
180 </body>
181 <body>
182
183 <p>
184 Next select <e>Maintain a devtmpfs file system to mount at /dev</e> so that
185 critical device files are already available early in the boot process.
186 </p>
187
188 <pre caption="Enabling devtmpfs support">
189 Device Drivers ---&gt;
190 Generic Driver Options ---&gt;
191 [*] Maintain a devtmpfs filesystem to mount at /dev
192 [ ] Automount devtmpfs at /dev, after the kernel mounted the rootfs
193 </pre>
194
195 <p>
196 Now go to <c>File Systems</c> and select support for the filesystems you use.
197 <e>Don't</e> compile the file system you use for the root filesystem as module,
198 otherwise your Gentoo system will not be able to mount your partition. Also
199 select <c>Virtual memory</c> and <c>/proc file system</c>.
200 </p>
201
202 <pre caption="Selecting necessary file systems">
203 File systems ---&gt;
204 <comment>(Select one or more of the following options as needed by your system)</comment>
205 &lt;*&gt; Second extended fs support
206 &lt;*&gt; Ext3 journalling file system support
207 &lt;*&gt; The Extended 4 (ext4) filesystem
208 &lt;*&gt; Reiserfs support
209 &lt;*&gt; JFS filesystem support
210 &lt;*&gt; XFS filesystem support
211 ...
212 Pseudo Filesystems ---&gt;
213 [*] /proc file system support
214 [*] Virtual memory file system support (former shm fs)
215
216 <comment>(Enable GPT partition label support if you used that previously)</comment>
217 -*- Enable the block layer --->
218 ...
219 Partition Types --->
220 [*] Advanced partition selection
221 ...
222 [*] EFI GUID Partition support
223 </pre>
224
225 <p>
226 If you are using PPPoE to connect to the Internet or you are using a dial-up
227 modem, you will need the following options in the kernel:
228 </p>
229
230 <pre caption="Selecting PPPoE necessary drivers">
231 Device Drivers ---&gt;
232 Network device support ---&gt;
233 &lt;*&gt; PPP (point-to-point protocol) support
234 &lt;*&gt; PPP support for async serial ports
235 &lt;*&gt; PPP support for sync tty ports
236 </pre>
237
238 <p>
239 The two compression options won't harm but are not definitely needed, neither
240 does the <c>PPP over Ethernet</c> option, that might only be used by <c>ppp</c>
241 when configured to do kernel mode PPPoE.
242 </p>
243
244 <p>
245 If you require it, don't forget to include support in the kernel for your
246 ethernet card.
247 </p>
248
249 <p test="func:keyval('arch')='x86'">
250 If you have an Intel CPU that supports HyperThreading (tm), or you have a
251 multi-CPU system, you should activate "Symmetric multi-processing support":
252 </p>
253
254 <p test="func:keyval('arch')='AMD64'">
255 If you have a multi-CPU Opteron or a multi-core (e.g. AMD64 X2) system, you
256 should activate "Symmetric multi-processing support":
257 </p>
258
259 <pre caption="Activating SMP support">
260 Processor type and features ---&gt;
261 [*] Symmetric multi-processing support
262 </pre>
263
264 <note>
265 In multi-core systems, each core counts as one processor.
266 </note>
267
268 <p test="func:keyval('arch')='x86'">
269 If you have more than 4GB of RAM, you need to enable "High Memory Support
270 (64G)".
271 </p>
272
273 <p>
274 If you use USB Input Devices (like Keyboard or Mouse) don't forget to enable
275 those as well:
276 </p>
277
278 <pre caption="Activating USB Support for Input Devices">
279 Device Drivers ---&gt;
280 [*] HID Devices ---&gt;
281 &lt;*&gt; USB Human Interface Device (full HID) support
282 </pre>
283
284 </body>
285 <body test="func:keyval('arch')='x86'">
286
287 <p>
288 If you want PCMCIA support for your laptop, don't forget to enable
289 support for the PCMCIA card bridge present in your system:
290 </p>
291
292 <pre caption="Enabling PCMCIA support">
293 Bus options (PCI etc.) ---&gt;
294 PCCARD (PCMCIA/CardBus) support ---&gt;
295 &lt;*&gt; PCCard (PCMCIA/CardBus) support
296 <comment>(select 16 bit if you need support for older PCMCIA cards. Most people want this.)</comment>
297 &lt;*&gt; 16-bit PCMCIA support
298 [*] 32-bit CardBus support
299 <comment>(select the relevant bridges below)</comment>
300 *** PC-card bridges ***
301 &lt;*&gt; CardBus yenta-compatible bridge support (NEW)
302 &lt;*&gt; Cirrus PD6729 compatible bridge support (NEW)
303 &lt;*&gt; i82092 compatible bridge support (NEW)
304 </pre>
305
306 <p>
307 When you've finished configuring the kernel, continue with <uri
308 link="#compiling">Compiling and Installing</uri>.
309 </p>
310
311 </body>
312 </subsection>
313 <subsection id="compiling">
314 <title>Compiling and Installing</title>
315 <body>
316
317 <p>
318 Now that your kernel is configured, it is time to compile and install it. Exit
319 the configuration and start the compilation process:
320 </p>
321
322 <pre caption="Compiling the kernel">
323 # <i>make &amp;&amp; make modules_install</i>
324 </pre>
325
326 <p>
327 When the kernel has finished compiling, copy the kernel image to
328 <path>/boot</path>. This is handled by the <c>make install</c> command:
329 </p>
330
331 <pre caption="Installing the kernel">
332 # <i>make install</i>
333 </pre>
334
335 <p>
336 This will copy the kernel image into <path>/boot</path> together with the
337 <path>System.map</path> file and the kernel configuration file.
338 </p>
339
340 </body>
341 </subsection>
342 <subsection>
343 <include href="hb-install-initramfs.xml"/>
344 </subsection>
345
346 </section>
347 <section id="genkernel">
348 <title>Alternative: Using genkernel</title>
349 <body>
350
351 <p>
352 If you are reading this section, you have chosen to use our <c>genkernel</c>
353 script to configure your kernel for you.
354 </p>
355
356 <p>
357 Now that your kernel source tree is installed, it's now time to compile your
358 kernel by using our <c>genkernel</c> script to automatically build a kernel for
359 you. <c>genkernel</c> works by configuring a kernel nearly identically to the
360 way our Installation CD kernel is configured. This means that when you use
361 <c>genkernel</c> to build your kernel, your system will generally detect all
362 your hardware at boot-time, just like our Installation CD does. Because
363 genkernel doesn't require any manual kernel configuration, it is an ideal
364 solution for those users who may not be comfortable compiling their own kernels.
365 </p>
366
367 <p>
368 Now, let's see how to use genkernel. First, emerge the genkernel ebuild:
369 </p>
370
371 <pre caption="Emerging genkernel">
372 # <i>emerge genkernel</i>
373 </pre>
374
375 <p>
376 Next, edit the <path>/etc/fstab</path> file so that the line containing
377 <path>/boot</path> as second field has the first field pointing to the right
378 device. If the partitioning example from the handbook is followed, then this
379 device is most likely <path><keyval id="/boot"/></path> with the ext2 file
380 system. This would make the entry in the file look like so:
381 </p>
382
383 <pre caption="Editing /etc/fstab for the /boot entry">
384 # <i>nano -w /etc/fstab</i>
385 ...
386 <keyval id="/boot"/> /boot ext2 defaults 0 2
387 </pre>
388
389 <p>
390 The remainder of the <path>/etc/fstab</path> will be updated in the next section,
391 but as <c>genkernel</c> reads this information we need to update the
392 <path>/boot</path> line up front.
393 </p>
394
395 <p>
396 Now, compile your kernel sources by running <c>genkernel all</c>. Be aware
397 though, as <c>genkernel</c> compiles a kernel that supports almost all
398 hardware, this compilation will take quite a while to finish!
399 </p>
400
401 <p>
402 Note that, if your boot partition doesn't use ext2 or ext3 as filesystem you
403 might need to manually configure your kernel using <c>genkernel --menuconfig
404 all</c> and add support for your filesystem <e>in</e> the kernel (i.e.
405 <e>not</e> as a module). Users of LVM2 will probably want to add <c>--lvm</c>
406 as an argument as well.
407 </p>
408
409 <pre caption="Running genkernel">
410 # <i>genkernel all</i>
411 </pre>
412
413 <p>
414 Once <c>genkernel</c> completes, a kernel, full set of modules and
415 <e>initial ram disk</e> (initramfs) will be created. We will use the kernel
416 and initrd when configuring a boot loader later in this document. Write
417 down the names of the kernel and initrd as you will need it when writing
418 the bootloader configuration file. The initrd will be started immediately after
419 booting to perform hardware autodetection (just like on the Installation CD)
420 before your "real" system starts up.
421 </p>
422
423 <pre caption="Checking the created kernel image name and initrd">
424 # <i>ls /boot/kernel* /boot/initramfs*</i>
425 </pre>
426
427 </body>
428 </section>
429 <section id="kernel_modules">
430 <title>Kernel Modules</title>
431
432 <subsection>
433 <include href="hb-install-kernelmodules.xml"/>
434 </subsection>
435
436 </section>
437 </sections>

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