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1 <?xml version="1.0" encoding="UTF-8"?>
2 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/kernel-upgrade.xml,v 1.7 2005/05/25 17:17:27 swift 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/2.0 -->
18 <license/>
19
20 <version>0.1.6</version>
21 <date>2005-06-04</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 If you really want to do it yourself, the following example shows you how to
139 make the link point to <path>linux-2.6.9-gentoo-r2</path>:
140 </p>
141
142 <pre caption="Updating the /usr/src/linux softlink manually">
143 # <i>cd /usr/src</i>
144 # <i>ln -sfn linux-2.6.9-gentoo-r2 linux</i>
145 </pre>
146
147 </body>
148 </section>
149 </chapter>
150
151 <chapter id="install">
152 <title>Configuring, compiling and installing the new kernel</title>
153 <section>
154 <body>
155
156 <p>
157 For either of these options, you should refer to the instructions given in the
158 <uri link="/doc/en/handbook/index.xml">Gentoo
159 Handbook</uri> relating to <e>Configuring the Kernel</e> and <e>Configuring
160 the Bootloader</e>. Below is an outline of the required actions:
161 </p>
162
163 </body>
164 </section>
165 <section>
166 <title>Option 1: Automatic kernel setup with Genkernel</title>
167 <body>
168
169 <p>
170 If you are a genkernel user, you just need to repeat the stages you went
171 through when installing your kernel for the first time.
172 </p>
173
174 <p>
175 Simply run genkernel in the normal way:
176 </p>
177
178 <pre caption="Invoking genkernel">
179 <comment>(For 2.4 kernels:)</comment>
180 # <i>genkernel all</i>
181
182 <comment>(For 2.6 kernels:)</comment>
183 # <i>genkernel --udev all</i>
184 </pre>
185
186 <p>
187 You can also use extra parameters for other genkernel functionality. For
188 example, if you wish to configure some extra kernel options using
189 <c>menuconfig</c> and you wish genkernel to automatically update your grub
190 boot loader configuration, then invoke genkernel as follows:
191 </p>
192
193 <pre caption="Invoking genkernel with some common arguments">
194 # <i>genkernel --menuconfig --bootloader=grub all</i>
195 </pre>
196
197 <p>
198 For more info, follow the
199 <uri link="/doc/en/genkernel.xml">Gentoo Linux Genkernel
200 Guide</uri>, or refer to the <uri link="/doc/en/handbook/index.xml">Gentoo
201 Handbook</uri>. Many of the options can be set in the configuration file for
202 <c>genkernel</c>, <path>/etc/genkernel.conf</path>.
203 </p>
204
205 </body>
206 </section>
207 <section>
208 <title>Option 2: Manual configuration</title>
209 <body>
210
211 <p>
212 To begin, open the <c>menuconfig</c> utility in the kernel source tree:
213 </p>
214
215 <pre caption="Invoking menuconfig">
216 # <i>cd /usr/src/linux</i>
217 # <i>make menuconfig</i>
218 </pre>
219
220 <p>
221 Select the options required for your hardware and operating environment. For
222 additional information on kernel configuration, refer to the chapter entitled
223 <e>Configuring the Kernel</e> of the <uri
224 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
225 </p>
226
227 <p>
228 Next, compile your kernel and copy it over to your boot partition. Again,
229 follow the <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
230 instructions outlined in the chapter on <e>Configuring the Bootloader</e>. If
231 <path>/boot</path> is a separate partition, ensure it is mounted before copying
232 the compiled kernel to this directory! Failing to do so would keep you from
233 booting the system with your new kernel.
234 </p>
235
236 <pre caption="Compiling and installing the new kernel">
237 # <i>make &amp;&amp; make modules_install</i>
238 # <i>mount /boot</i>
239 # <i>cp arch/i386/boot/bzImage /boot/bzImage-2.6.9-gentoo-r2</i>
240 # <i>cp System.map /boot/System.map-2.6.9-gentoo-r2</i>
241 </pre>
242
243 <p>
244 Finally, you should update your boot loader configuration, adding an entry for
245 the new kernel (don't delete the old one just yet!) and unmount the
246 <path>/boot</path> partition. Again, refer to the
247 <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
248 for detailed instructions on this procedure.
249 </p>
250
251 </body>
252 </section>
253 </chapter>
254
255 <chapter>
256 <title>Reinstalling external modules</title>
257 <section>
258 <body>
259
260 <p>
261 If you use any kernel modules that are not included in the kernel source tree
262 but are provided elsewhere in portage (e.g. NVIDIA or ATI graphics drivers),
263 then you must reinstall these after upgrading the kernel. This is as simple as
264 re-merging the packages involved. For more information, refer to the chapter on
265 <e>Configuring the Kernel</e> in the <uri
266 link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
267 To ensure these packages will build against the source tree at
268 <path>/usr/src/linux</path>, first uninstall the packages, then re-emerge them.
269 If old sources for these packages are kept by portage, this uninstall/re-emerge
270 procedure will make sure that they are rebuilt to work with the new kernel.
271 </p>
272
273 </body>
274 </section>
275 </chapter>
276
277 <chapter>
278 <title>Rebooting into the new kernel</title>
279 <section>
280 <body>
281
282 <p>
283 Next, close all applications and reboot your system. If you followed the above
284 instructions correctly, the boot loader menu should include an entry for the
285 new kernel. Select the new kernel and let the system boot.
286 </p>
287
288 <p>
289 Hopefully, your system successfully boots with the new kernel, and you can log
290 in to resume whatever you were doing. If this is the case, then the upgrade is
291 complete.
292 </p>
293
294 <p>
295 If you made a mistake and the system fails to boot with the new kernel, reboot
296 the system and select the entry from the boot loader that corresponds to the
297 last known working kernel. You can then restart from the <uri link="#install">
298 Configuring, compiling, and installing the new kernel</uri> stage -- making
299 the appropriate changes to correct your mistake. In some cases, you might not
300 even need to reboot to do this (e.g. you missed a driver for an audio device,
301 Ethernet adapter, etc.)
302 </p>
303
304 </body>
305 </section>
306 </chapter>
307
308 <chapter>
309 <title>Running multiple kernels</title>
310 <section>
311 <body>
312
313 <p>
314 You may have noticed, that when installing the sources for your newer kernel,
315 the sources for your existing kernel were not removed. This is by design -- it
316 allows you to easily switch between running different kernels.
317 </p>
318
319 <p>
320 Switching between multiple kernels is as simple as leaving the kernel sources
321 under <path>/usr/src/</path> and leaving the <path>bzImage</path> binaries on
322 your <path>/boot</path> partition (referenced by entries in your boot loader
323 configuration). Every time you boot up, you will be presented with a choice of
324 which kernel to boot into.
325 </p>
326
327 </body>
328 </section>
329 </chapter>
330
331 <chapter>
332 <title>Removing older kernels</title>
333 <section>
334 <body>
335
336 <p>
337 Continuing on from the last section, you may be happy with your new kernel and
338 not have any need to keep older kernel versions around. To easily remove all
339 sources for a particular kernel except for the newest one, you can take
340 advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
341 the example using <c>gentoo-sources</c>:
342 </p>
343
344 <pre caption="Pruning old versions">
345 # <i>emerge -P gentoo-sources</i>
346 </pre>
347
348 <p>
349 In most cases, temporary files used during compilation will still remain under
350 the appropriate source directory under <path>/usr/src</path>. It is safe to
351 remove these using <c>rm</c>.
352 </p>
353
354 <p>
355 You can also safely delete any modules that were used by this kernel. This can
356 be done by removing the appropriate directories under <path>/lib/modules/</path>
357 that relate to the kernel versions you are removing. Be careful not to delete
358 modules belonging to kernels that you still use!
359 </p>
360
361 <p>
362 Finally, you can mount your <path>/boot</path> partition and remove the
363 <path>bzImage</path> and <path>System.map</path> files for the kernel(s)
364 you are pruning. You should also edit your boot loader configuration so that it
365 no longer references such kernel(s).
366 </p>
367
368 </body>
369 </section>
370 </chapter>
371
372 <chapter>
373 <title>Advanced: Using your old kernel .config to configure a new one</title>
374 <section>
375 <body>
376
377 <p>
378 It is sometimes possible to save time by re-using the configuration file from
379 your old kernel when configuring the new one. Note that this is generally
380 unsafe -- too many changes between every kernel release for this to be a
381 reliable upgrade path.
382 </p>
383
384 <p>
385 The only situation where this is appropriate is when upgrading from one Gentoo
386 kernel revision to another. For example, the changes made between
387 <c>gentoo-sources-2.6.9-r1</c> and <c>gentoo-sources-2.6.9-r2</c> will be very
388 small, so it is usually OK to use the following method. However, it is not
389 appropriate to use it in the example used throughout this document: upgrading
390 from 2.6.8 to 2.6.9. Too many changes between the official releases, and the
391 method described below does not display enough context to the user, often
392 resulting in the user running into problems because they disabled options that
393 they really didn't want to.
394 </p>
395
396 <p>
397 To reuse your old <path>.config</path>, you simply need to copy it over and then
398 run <c>make oldconfig</c>. In the following example, we take the configuration
399 from <c>gentoo-sources-2.6.9-r1</c> and import it into
400 <c>gentoo-sources-2.6.9-r2</c>.
401 </p>
402
403 <pre caption="Reusing your old config">
404 # <i>cd /usr/src/linux-2.6.9-gentoo-r2</i>
405 # <i>cp ../linux-2.6.9-gentoo-r1/.config .</i>
406 # <i>make oldconfig</i>
407 </pre>
408
409 <p>
410 At this point, you may be asked to produce answers for configuration options
411 which have changed between the two versions. Once you have done that, you can
412 compile and install your kernel as normal, without having to go through the
413 <c>menuconfig</c> configuration process.
414 </p>
415
416 </body>
417 </section>
418 </chapter>
419
420 <chapter>
421 <title>Problems after a kernel upgrade?</title>
422 <section>
423 <body>
424
425 <p>
426 With the rapid development of the Linux kernel, it is inevitable that some
427 changes made from one kernel release to another may cause some problems. If you
428 have any issues with the latest versions of <uri
429 link="/doc/en/gentoo-kernel.xml#doc_chap2"> Gentoo-supported kernels</uri> then
430 please do report the issues to us.
431 </p>
432
433 </body>
434 </section>
435 </chapter>
436
437 </guide>

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