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#138582 no need for --udev w/ genkernel anymore, how to reuse config with genkernel

1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/kernel-upgrade.xml,v 1.15 2006/05/04 16:49:14 fox2mike Exp $ -->
3
4 <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
5 <guide link="/doc/en/kernel-upgrade.xml">
6 <title>Gentoo Linux Kernel Upgrade Guide</title>
7 <author title="Author">
8 <mail link="dsd@gentoo.org">Daniel Drake</mail>
9 </author>
10
11 <abstract>
12 This document describes the process of upgrading your kernel from one release
13 to another.
14 </abstract>
15
16 <!-- The content of this document is licensed under the CC-BY-SA license -->
17 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
18 <license/>
19
20 <version>0.5</version>
21 <date>2006-07-23</date>
22
23 <chapter>
24 <title>Introduction</title>
25 <section>
26 <body>
27
28 <p>
29 The kernel is one of the few package classes in portage that requires some
30 manual intervention to complete the upgrade. Portage will download and
31 install the kernel source for you, but then it is up to you to step in and
32 compile the new kernel before any changes will take effect.
33 </p>
34
35 <p>
36 Although this guide is targeted at users upgrading from one kernel release
37 to another, it will also be useful for users migrating from one kernel
38 package to another.
39 </p>
40
41 <p>
42 <c>gentoo-sources</c> is used as an example in this document, however, the
43 instructions here also apply to the other packages present in our tree.
44 </p>
45
46 </body>
47 </section>
48 </chapter>
49
50 <chapter>
51 <title>Why upgrade the kernel?</title>
52 <section>
53 <body>
54
55 <p>
56 Generally, upgrading from one minor kernel release to the next won't bring any
57 major differences. There are several reasons to upgrade the kernel. One is to
58 take advantage of a specific new feature or driver; another is to be protected
59 against a security vulnerability, or just to maintain an up-to-date and healthy
60 system.
61 </p>
62
63 <p>
64 Even if you choose not to update to every new kernel revision, it is
65 recommended that you at least upgrade from time to time. It is strongly
66 recommended that you immediately upgrade to a new kernel if that new release
67 solves a security problem.
68 </p>
69
70 </body>
71 </section>
72 </chapter>
73
74 <chapter>
75 <title>Obtaining the newer sources through Portage</title>
76 <section>
77 <body>
78
79 <p>
80 You upgrade the kernel sources like you would upgrade any other package -
81 using the <c>emerge</c> utility. It will probably be the case that you want to
82 upgrade your kernel when you see the upgrade appearing on your world updates
83 list. For example:
84 </p>
85
86 <pre caption="New kernel sources appearing on update list">
87 # <i>emerge -Dup world</i>
88 Calculating dependencies ...done!
89 [ebuild NS ] sys-kernel/gentoo-sources-2.6.9-r2 [2.6.8-r5]
90 </pre>
91
92 <note>
93 The "NS" label in the above output means that the new kernel will be installed
94 in a New Slot, i.e. the sources of your old kernel will be kept around, until
95 you manually remove them.
96 </note>
97
98 <p>
99 You can then go ahead and install the update, e.g.:
100 </p>
101
102 <pre caption="Upgrading your kernel sources">
103 # <i>emerge -u gentoo-sources</i>
104 </pre>
105
106 <p>
107 The kernel sources will then be installed into a subdirectory of
108 <path>/usr/src</path>. In the above example, the new kernel sources will be
109 installed at <path>/usr/src/linux-2.6.9-gentoo-r2</path>.
110 </p>
111
112 </body>
113 </section>
114 </chapter>
115
116 <chapter>
117 <title>Updating the /usr/src/linux symbolic link</title>
118 <section>
119 <body>
120
121 <p>
122 Gentoo requires that the <path>/usr/src/linux</path> symbolic link points to
123 the sources of the kernel you are running.
124 </p>
125
126 <p>
127 Portage can update the symlink automatically when you emerge new kernel
128 sources. All you have to do is add the <c>symlink</c> flag to the USE variable
129 in <path>/etc/make.conf</path>.
130 </p>
131
132 <pre caption="Example of USE variable in /etc/make.conf">
133 <comment>(Add the symlink keyword)</comment>
134 USE="<i>symlink</i> x86 3dnow 3dnowex X aac aalib adns alsa apache2"
135 </pre>
136
137 <p>
138 Alternatively, you could use <c>app-admin/eselect</c> to modify the symlink.
139 </p>
140
141 <pre caption="Using eselect to symlink">
142 <comment>(Install eselect if you don't have it)</comment>
143 # <i>emerge eselect</i>
144 <comment>(See the list of available kernels)</comment>
145 # <i>eselect kernel list</i>
146 Available kernel symlink targets:
147 [1] linux-2.6.9-gentoo-r1
148 [2] linux-2.6.9-gentoo-r2
149 <comment>(Select the correct kernel)</comment>
150 # <i>eselect kernel set 1</i>
151 </pre>
152
153 <p>
154 If you really want to do it yourself, the following example shows you how to
155 make the link point to <path>linux-2.6.9-gentoo-r2</path>:
156 </p>
157
158 <pre caption="Updating the /usr/src/linux softlink manually">
159 # <i>cd /usr/src</i>
160 # <i>ln -sfn linux-2.6.9-gentoo-r2 linux</i>
161 </pre>
162
163 </body>
164 </section>
165 </chapter>
166
167 <chapter id="install">
168 <title>Configuring, compiling and installing the new kernel</title>
169 <section>
170 <body>
171
172 <p>
173 For either of these options, you should refer to the instructions given in the
174 <uri link="/doc/en/handbook/">Gentoo Handbook</uri> relating to <e>Configuring
175 the Kernel</e> and <e>Configuring the Bootloader</e>. Below is an outline of
176 the required actions:
177 </p>
178
179 </body>
180 </section>
181 <section>
182 <title>Option 1: Automatic kernel setup with Genkernel</title>
183 <body>
184
185 <p>
186 If you are a genkernel user, you just need to repeat the stages you went
187 through when installing your kernel for the first time.
188 </p>
189
190 <p>
191 Simply run genkernel in the normal way:
192 </p>
193
194 <pre caption="Invoking genkernel">
195 # <i>genkernel all</i>
196 </pre>
197
198 <p>
199 You can also use extra parameters for other genkernel functionality. For
200 example, if you wish to configure some extra kernel options using
201 <c>menuconfig</c> and you wish genkernel to automatically update your grub boot
202 loader configuration, then invoke genkernel as follows:
203 </p>
204
205 <pre caption="Invoking genkernel with some common arguments">
206 # <i>genkernel --menuconfig --bootloader=grub all</i>
207 </pre>
208
209 <p>
210 For more info, follow the <uri link="/doc/en/genkernel.xml">Gentoo Linux
211 Genkernel Guide</uri>, or refer to the <uri link="/doc/en/handbook/">Gentoo
212 Handbook</uri>. Many of the options can be set in the configuration file for
213 <c>genkernel</c>, <path>/etc/genkernel.conf</path>.
214 </p>
215
216 </body>
217 </section>
218 <section>
219 <title>Option 2: Manual configuration</title>
220 <body>
221
222 <p>
223 To begin, open the <c>menuconfig</c> utility in the kernel source tree:
224 </p>
225
226 <pre caption="Invoking menuconfig">
227 # <i>cd /usr/src/linux</i>
228 # <i>make menuconfig</i>
229 </pre>
230
231 <p>
232 Select the options required for your hardware and operating environment. For
233 additional information on kernel configuration, refer to the chapter entitled
234 <e>Configuring the Kernel</e> of the <uri
235 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
236 </p>
237
238 <p>
239 Next, compile your kernel and copy it over to your boot partition. Again,
240 follow the <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
241 instructions outlined in the chapter on <e>Configuring the Bootloader</e>. If
242 <path>/boot</path> is a separate partition, ensure it is mounted before copying
243 the compiled kernel to this directory! Failing to do so would keep you from
244 booting the system with your new kernel.
245 </p>
246
247 <pre caption="Compiling and installing the new kernel">
248 # <i>make &amp;&amp; make modules_install</i>
249 # <i>mount /boot</i>
250 # <i>cp arch/i386/boot/bzImage /boot/bzImage-2.6.9-gentoo-r2</i>
251 </pre>
252
253 <p>
254 Finally, you should update your boot loader configuration, adding an entry for
255 the new kernel (don't delete the old one just yet!) and unmount the
256 <path>/boot</path> partition. Again, refer to the
257 <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
258 for detailed instructions on this procedure.
259 </p>
260
261 </body>
262 </section>
263 </chapter>
264
265 <chapter>
266 <title>Reinstalling external modules</title>
267 <section>
268 <body>
269
270 <p>
271 If you use any kernel modules that are not included in the kernel source tree
272 but are provided elsewhere in Portage (e.g. ALSA drivers and NVIDIA or ATI
273 graphics drivers), then you must reinstall these after upgrading the kernel.
274 This is as simple as re-merging the packages involved. For more information,
275 refer to the chapter on <e>Configuring the Kernel</e> in the <uri
276 link="/doc/en/handbook/">Gentoo Handbook</uri>.
277 </p>
278
279 <p>
280 We provide you with an easy tool (<c>sys-kernel/module-rebuild</c>) which
281 rebuilds all the kernel modules you have installed using separate ebuilds for
282 the kernel at <path>/usr/src/linux</path>. Its use is straightforward. After
283 emerging it, simply run <c>module-rebuild populate</c> to populate the
284 database with a list of packages that will need to be rebuilt after upgrading
285 the kernel. Once you have finished upgrading or recompiling your kernel, run
286 <c>module-rebuild rebuild</c> to rebuild the drivers for your new kernel.
287 </p>
288
289 <p>
290 For more information, run <c>module-rebuild</c> without any options to see a
291 list of commands that can be passed to the utility.
292 </p>
293
294 </body>
295 </section>
296 </chapter>
297
298 <chapter>
299 <title>Rebooting into the new kernel</title>
300 <section>
301 <body>
302
303 <p>
304 Next, close all applications and reboot your system. If you followed the above
305 instructions correctly, the boot loader menu should include an entry for the
306 new kernel. Select the new kernel and let the system boot.
307 </p>
308
309 <p>
310 Hopefully, your system successfully boots with the new kernel, and you can log
311 in to resume whatever you were doing. If this is the case, then the upgrade is
312 complete.
313 </p>
314
315 <p>
316 If you made a mistake and the system fails to boot with the new kernel, reboot
317 the system and select the entry from the boot loader that corresponds to the
318 last known working kernel. You can then restart from the <uri link="#install">
319 Configuring, compiling, and installing the new kernel</uri> stage -- making
320 the appropriate changes to correct your mistake. In some cases, you might not
321 even need to reboot to do this (e.g. you missed a driver for an audio device,
322 Ethernet adapter, etc.)
323 </p>
324
325 </body>
326 </section>
327 </chapter>
328
329 <chapter>
330 <title>Running multiple kernels</title>
331 <section>
332 <body>
333
334 <p>
335 You may have noticed, that when installing the sources for your newer kernel,
336 the sources for your existing kernel were not removed. This is by design -- it
337 allows you to easily switch between running different kernels.
338 </p>
339
340 <p>
341 Switching between multiple kernels is as simple as leaving the kernel sources
342 under <path>/usr/src/</path> and leaving the <path>bzImage</path> binaries on
343 your <path>/boot</path> partition (referenced by entries in your boot loader
344 configuration). Every time you boot up, you will be presented with a choice of
345 which kernel to boot into.
346 </p>
347
348 </body>
349 </section>
350 </chapter>
351
352 <chapter>
353 <title>Removing older kernels</title>
354 <section>
355 <body>
356
357 <p>
358 Continuing on from the last section, you may be happy with your new kernel and
359 not have any need to keep older kernel versions around. To easily remove all
360 sources for a particular kernel except for the newest one, you can take
361 advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
362 the example using <c>gentoo-sources</c>:
363 </p>
364
365 <pre caption="Pruning old versions">
366 # <i>emerge -P gentoo-sources</i>
367 </pre>
368
369 <p>
370 In most cases, temporary files used during compilation will still remain under
371 the appropriate source directory under <path>/usr/src</path>. It is safe to
372 remove these using <c>rm</c>.
373 </p>
374
375 <p>
376 You can also safely delete any modules that were used by this kernel. This can
377 be done by removing the appropriate directories under <path>/lib/modules/</path>
378 that relate to the kernel versions you are removing. Be careful not to delete
379 modules belonging to kernels that you still use!
380 </p>
381
382 <p>
383 Finally, you can mount your <path>/boot</path> partition and remove the
384 <path>bzImage</path> file(s) for the kernel(s) you are pruning. You should also
385 edit your boot loader configuration so that it no longer references such
386 kernel(s).
387 </p>
388
389 </body>
390 </section>
391 </chapter>
392
393 <chapter>
394 <title>Advanced: Using your old kernel .config to configure a new one</title>
395 <section>
396 <body>
397
398 <p>
399 It is sometimes possible to save time by re-using the configuration file from
400 your old kernel when configuring the new one. Note that this is generally
401 unsafe -- too many changes between every kernel release for this to be a
402 reliable upgrade path.
403 </p>
404
405 <p>
406 The only situation where this is appropriate is when upgrading from one Gentoo
407 kernel revision to another. For example, the changes made between
408 <c>gentoo-sources-2.6.9-r1</c> and <c>gentoo-sources-2.6.9-r2</c> will be very
409 small, so it is usually OK to use the following method. However, it is not
410 appropriate to use it in the example used throughout this document: upgrading
411 from 2.6.8 to 2.6.9. Too many changes between the official releases, and the
412 method described below does not display enough context to the user, often
413 resulting in the user running into problems because they disabled options that
414 they really didn't want to.
415 </p>
416
417 <p>
418 To reuse your old <path>.config</path>, you simply need to copy it over and
419 then run <c>make oldconfig</c>. In the following example, we take the
420 configuration from <c>gentoo-sources-2.6.9-r1</c> and import it into
421 <c>gentoo-sources-2.6.9-r2</c>.
422 </p>
423
424 <pre caption="Reusing your old config">
425 # <i>cd /usr/src/linux-2.6.9-gentoo-r2</i>
426 # <i>cp ../linux-2.6.9-gentoo-r1/.config .</i>
427 # <i>make oldconfig</i>
428 </pre>
429
430 <pre caption="Reusing your old config with genkernel">
431 # <i>cd /etc/kernels</i>
432 # <i>cp kernel-config-x86-2.6.9-gentoo-r1 kernel-config-x86-2.6.9-gentoo-r2</i>
433 # <i>genkernel all</i>
434 </pre>
435
436 <p>
437 At this point, you may be asked to produce answers for configuration options
438 which have changed between the two versions. Once you have done that, you can
439 compile and install your kernel as normal, without having to go through the
440 <c>menuconfig</c> configuration process.
441 </p>
442
443 </body>
444 </section>
445 </chapter>
446
447 <chapter>
448 <title>Problems after a kernel upgrade?</title>
449 <section>
450 <body>
451
452 <p>
453 With the rapid development of the Linux kernel, it is inevitable that some
454 changes made from one kernel release to another may cause some problems. If you
455 have any issues with the latest versions of <uri
456 link="/doc/en/gentoo-kernel.xml#doc_chap2"> Gentoo-supported kernels</uri> then
457 please do report the issues to us.
458 </p>
459
460 </body>
461 </section>
462 </chapter>
463
464 </guide>

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