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Bug #113417 - Added a few lines on using eselect to change the kernel symlink. Thanks to Federico Galassi<federico@serversidestudio.it> for reporting.

1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/kernel-upgrade.xml,v 1.14 2006/02/22 20:30:20 nightmorph 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>0.4</version>
21 <date>2006-05-04</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/index.xml">Gentoo
175 Handbook</uri> relating to <e>Configuring the Kernel</e> and <e>Configuring
176 the Bootloader</e>. Below is an outline of 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 <comment>(For 2.4 kernels:)</comment>
196 # <i>genkernel all</i>
197
198 <comment>(For 2.6 kernels:)</comment>
199 # <i>genkernel --udev all</i>
200 </pre>
201
202 <p>
203 You can also use extra parameters for other genkernel functionality. For
204 example, if you wish to configure some extra kernel options using
205 <c>menuconfig</c> and you wish genkernel to automatically update your grub
206 boot loader configuration, then invoke genkernel as follows:
207 </p>
208
209 <pre caption="Invoking genkernel with some common arguments">
210 # <i>genkernel --menuconfig --bootloader=grub all</i>
211 </pre>
212
213 <p>
214 For more info, follow the
215 <uri link="/doc/en/genkernel.xml">Gentoo Linux Genkernel
216 Guide</uri>, or refer to the <uri link="/doc/en/handbook/index.xml">Gentoo
217 Handbook</uri>. Many of the options can be set in the configuration file for
218 <c>genkernel</c>, <path>/etc/genkernel.conf</path>.
219 </p>
220
221 </body>
222 </section>
223 <section>
224 <title>Option 2: Manual configuration</title>
225 <body>
226
227 <p>
228 To begin, open the <c>menuconfig</c> utility in the kernel source tree:
229 </p>
230
231 <pre caption="Invoking menuconfig">
232 # <i>cd /usr/src/linux</i>
233 # <i>make menuconfig</i>
234 </pre>
235
236 <p>
237 Select the options required for your hardware and operating environment. For
238 additional information on kernel configuration, refer to the chapter entitled
239 <e>Configuring the Kernel</e> of the <uri
240 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
241 </p>
242
243 <p>
244 Next, compile your kernel and copy it over to your boot partition. Again,
245 follow the <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
246 instructions outlined in the chapter on <e>Configuring the Bootloader</e>. If
247 <path>/boot</path> is a separate partition, ensure it is mounted before copying
248 the compiled kernel to this directory! Failing to do so would keep you from
249 booting the system with your new kernel.
250 </p>
251
252 <pre caption="Compiling and installing the new kernel">
253 # <i>make &amp;&amp; make modules_install</i>
254 # <i>mount /boot</i>
255 # <i>cp arch/i386/boot/bzImage /boot/bzImage-2.6.9-gentoo-r2</i>
256 </pre>
257
258 <p>
259 Finally, you should update your boot loader configuration, adding an entry for
260 the new kernel (don't delete the old one just yet!) and unmount the
261 <path>/boot</path> partition. Again, refer to the
262 <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
263 for detailed instructions on this procedure.
264 </p>
265
266 </body>
267 </section>
268 </chapter>
269
270 <chapter>
271 <title>Reinstalling external modules</title>
272 <section>
273 <body>
274
275 <p>
276 If you use any kernel modules that are not included in the kernel source tree
277 but are provided elsewhere in Portage (e.g. ALSA drivers and NVIDIA or ATI
278 graphics drivers), then you must reinstall these after upgrading the kernel.
279 This is as simple as re-merging the packages involved. For more information,
280 refer to the chapter on <e>Configuring the Kernel</e> in the <uri
281 link="/doc/en/handbook/">Gentoo Handbook</uri>.
282 </p>
283
284 <p>
285 We provide you with an easy tool (<c>sys-kernel/module-rebuild</c>) which
286 rebuilds all the kernel modules you have installed using separate ebuilds for
287 the kernel at <path>/usr/src/linux</path>. Its use is straightforward. After
288 emerging it, simply run <c>module-rebuild populate</c> to populate the
289 database with a list of packages that will need to be rebuilt after upgrading
290 the kernel. Once you have finished upgrading or recompiling your kernel, run
291 <c>module-rebuild rebuild</c> to rebuild the drivers for your new kernel.
292 </p>
293
294 <p>
295 For more information, run <c>module-rebuild</c> without any options to see a
296 list of commands that can be passed to the utility.
297 </p>
298
299 </body>
300 </section>
301 </chapter>
302
303 <chapter>
304 <title>Rebooting into the new kernel</title>
305 <section>
306 <body>
307
308 <p>
309 Next, close all applications and reboot your system. If you followed the above
310 instructions correctly, the boot loader menu should include an entry for the
311 new kernel. Select the new kernel and let the system boot.
312 </p>
313
314 <p>
315 Hopefully, your system successfully boots with the new kernel, and you can log
316 in to resume whatever you were doing. If this is the case, then the upgrade is
317 complete.
318 </p>
319
320 <p>
321 If you made a mistake and the system fails to boot with the new kernel, reboot
322 the system and select the entry from the boot loader that corresponds to the
323 last known working kernel. You can then restart from the <uri link="#install">
324 Configuring, compiling, and installing the new kernel</uri> stage -- making
325 the appropriate changes to correct your mistake. In some cases, you might not
326 even need to reboot to do this (e.g. you missed a driver for an audio device,
327 Ethernet adapter, etc.)
328 </p>
329
330 </body>
331 </section>
332 </chapter>
333
334 <chapter>
335 <title>Running multiple kernels</title>
336 <section>
337 <body>
338
339 <p>
340 You may have noticed, that when installing the sources for your newer kernel,
341 the sources for your existing kernel were not removed. This is by design -- it
342 allows you to easily switch between running different kernels.
343 </p>
344
345 <p>
346 Switching between multiple kernels is as simple as leaving the kernel sources
347 under <path>/usr/src/</path> and leaving the <path>bzImage</path> binaries on
348 your <path>/boot</path> partition (referenced by entries in your boot loader
349 configuration). Every time you boot up, you will be presented with a choice of
350 which kernel to boot into.
351 </p>
352
353 </body>
354 </section>
355 </chapter>
356
357 <chapter>
358 <title>Removing older kernels</title>
359 <section>
360 <body>
361
362 <p>
363 Continuing on from the last section, you may be happy with your new kernel and
364 not have any need to keep older kernel versions around. To easily remove all
365 sources for a particular kernel except for the newest one, you can take
366 advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
367 the example using <c>gentoo-sources</c>:
368 </p>
369
370 <pre caption="Pruning old versions">
371 # <i>emerge -P gentoo-sources</i>
372 </pre>
373
374 <p>
375 In most cases, temporary files used during compilation will still remain under
376 the appropriate source directory under <path>/usr/src</path>. It is safe to
377 remove these using <c>rm</c>.
378 </p>
379
380 <p>
381 You can also safely delete any modules that were used by this kernel. This can
382 be done by removing the appropriate directories under <path>/lib/modules/</path>
383 that relate to the kernel versions you are removing. Be careful not to delete
384 modules belonging to kernels that you still use!
385 </p>
386
387 <p>
388 Finally, you can mount your <path>/boot</path> partition and remove the
389 <path>bzImage</path> file(s) for the kernel(s) you are pruning. You should also
390 edit your boot loader configuration so that it no longer references such
391 kernel(s).
392 </p>
393
394 </body>
395 </section>
396 </chapter>
397
398 <chapter>
399 <title>Advanced: Using your old kernel .config to configure a new one</title>
400 <section>
401 <body>
402
403 <p>
404 It is sometimes possible to save time by re-using the configuration file from
405 your old kernel when configuring the new one. Note that this is generally
406 unsafe -- too many changes between every kernel release for this to be a
407 reliable upgrade path.
408 </p>
409
410 <p>
411 The only situation where this is appropriate is when upgrading from one Gentoo
412 kernel revision to another. For example, the changes made between
413 <c>gentoo-sources-2.6.9-r1</c> and <c>gentoo-sources-2.6.9-r2</c> will be very
414 small, so it is usually OK to use the following method. However, it is not
415 appropriate to use it in the example used throughout this document: upgrading
416 from 2.6.8 to 2.6.9. Too many changes between the official releases, and the
417 method described below does not display enough context to the user, often
418 resulting in the user running into problems because they disabled options that
419 they really didn't want to.
420 </p>
421
422 <p>
423 To reuse your old <path>.config</path>, you simply need to copy it over and then
424 run <c>make oldconfig</c>. In the following example, we take the configuration
425 from <c>gentoo-sources-2.6.9-r1</c> and import it into
426 <c>gentoo-sources-2.6.9-r2</c>.
427 </p>
428
429 <pre caption="Reusing your old config">
430 # <i>cd /usr/src/linux-2.6.9-gentoo-r2</i>
431 # <i>cp ../linux-2.6.9-gentoo-r1/.config .</i>
432 # <i>make oldconfig</i>
433 </pre>
434
435 <p>
436 At this point, you may be asked to produce answers for configuration options
437 which have changed between the two versions. Once you have done that, you can
438 compile and install your kernel as normal, without having to go through the
439 <c>menuconfig</c> configuration process.
440 </p>
441
442 </body>
443 </section>
444 </chapter>
445
446 <chapter>
447 <title>Problems after a kernel upgrade?</title>
448 <section>
449 <body>
450
451 <p>
452 With the rapid development of the Linux kernel, it is inevitable that some
453 changes made from one kernel release to another may cause some problems. If you
454 have any issues with the latest versions of <uri
455 link="/doc/en/gentoo-kernel.xml#doc_chap2"> Gentoo-supported kernels</uri> then
456 please do report the issues to us.
457 </p>
458
459 </body>
460 </section>
461 </chapter>
462
463 </guide>

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