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1 swift 1.1 <?xml version="1.0" encoding="UTF-8"?>
2 swift 1.20 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/kernel-upgrade.xml,v 1.19 2011/05/29 00:39:18 nightmorph Exp $ -->
3 swift 1.1
4     <!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
5 neysx 1.3 <guide link="/doc/en/kernel-upgrade.xml">
6 swift 1.1 <title>Gentoo Linux Kernel Upgrade Guide</title>
7     <author title="Author">
8 neysx 1.12 <mail link="dsd@gentoo.org">Daniel Drake</mail>
9 swift 1.1 </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 jkt 1.9 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
18 swift 1.1 <license/>
19    
20 swift 1.20 <version>2</version>
21     <date>2011-09-04</date>
22 swift 1.1
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 swift 1.4 Although this guide is targeted at users upgrading from one kernel release
37 swift 1.1 to another, it will also be useful for users migrating from one kernel
38     package to another.
39     </p>
40    
41     <p>
42 neysx 1.3 <c>gentoo-sources</c> is used as an example in this document, however, the
43 swift 1.1 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 swift 1.4 <title>Why upgrade the kernel?</title>
52 swift 1.1 <section>
53     <body>
54    
55     <p>
56     Generally, upgrading from one minor kernel release to the next won't bring any
57 swift 1.4 major differences. There are several reasons to upgrade the kernel. One is to
58 swift 1.18 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 swift 1.4 system.
61 swift 1.1 </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 swift 1.20 [ebuild NS ] sys-kernel/gentoo-sources-2.6.39-r3 [2.6.38-r6]
90 swift 1.1 </pre>
91    
92 neysx 1.3 <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 swift 1.1 <p>
99     You can then go ahead and install the update, e.g.:
100     </p>
101    
102     <pre caption="Upgrading your kernel sources">
103 neysx 1.3 # <i>emerge -u gentoo-sources</i>
104 swift 1.1 </pre>
105    
106     <p>
107 swift 1.18 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 swift 1.20 installed at <path>/usr/src/linux-2.6.39-gentoo-r3</path>.
110 swift 1.1 </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 neysx 1.8 Gentoo requires that the <path>/usr/src/linux</path> symbolic link points to
123     the sources of the kernel you are running.
124 swift 1.1 </p>
125    
126     <p>
127 neysx 1.8 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 swift 1.1 </p>
131    
132 neysx 1.8 <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 fox2mike 1.15 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 swift 1.20 [1] linux-2.6.39-gentoo-r3
148     [2] linux-2.6.38-gentoo-r6 *
149 fox2mike 1.15 <comment>(Select the correct kernel)</comment>
150     # <i>eselect kernel set 1</i>
151 nightmorph 1.19 <comment>(Verify the kernel was symlinked)</comment>
152     # <i>eselect kernel list</i>
153 swift 1.20 [1] linux-2.6.39-gentoo-r3 *
154     [2] linux-2.6.38-gentoo-r6
155 fox2mike 1.15 </pre>
156    
157     <p>
158 neysx 1.8 If you really want to do it yourself, the following example shows you how to
159 swift 1.20 make the link point to <path>linux-2.6.39-gentoo-r3</path>:
160 neysx 1.8 </p>
161    
162     <pre caption="Updating the /usr/src/linux softlink manually">
163 swift 1.1 # <i>cd /usr/src</i>
164 swift 1.20 # <i>ln -sfn linux-2.6.39-gentoo-r3 linux</i>
165 swift 1.1 </pre>
166    
167     </body>
168     </section>
169     </chapter>
170    
171     <chapter id="install">
172     <title>Configuring, compiling and installing the new kernel</title>
173     <section>
174     <body>
175    
176     <p>
177     For either of these options, you should refer to the instructions given in the
178 neysx 1.16 <uri link="/doc/en/handbook/">Gentoo Handbook</uri> relating to <e>Configuring
179     the Kernel</e> and <e>Configuring the Bootloader</e>. Below is an outline of
180     the required actions:
181 swift 1.1 </p>
182    
183     </body>
184     </section>
185     <section>
186     <title>Option 1: Automatic kernel setup with Genkernel</title>
187     <body>
188    
189     <p>
190     If you are a genkernel user, you just need to repeat the stages you went
191     through when installing your kernel for the first time.
192     </p>
193    
194     <p>
195     Simply run genkernel in the normal way:
196     </p>
197    
198     <pre caption="Invoking genkernel">
199     # <i>genkernel 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 neysx 1.16 <c>menuconfig</c> and you wish genkernel to automatically update your grub boot
206     loader configuration, then invoke genkernel as follows:
207 swift 1.1 </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 neysx 1.16 For more info, follow the <uri link="/doc/en/genkernel.xml">Gentoo Linux
215     Genkernel Guide</uri>, or refer to the <uri link="/doc/en/handbook/">Gentoo
216 swift 1.4 Handbook</uri>. Many of the options can be set in the configuration file for
217 swift 1.6 <c>genkernel</c>, <path>/etc/genkernel.conf</path>.
218 swift 1.1 </p>
219    
220     </body>
221     </section>
222     <section>
223     <title>Option 2: Manual configuration</title>
224     <body>
225    
226     <p>
227     To begin, open the <c>menuconfig</c> utility in the kernel source tree:
228     </p>
229    
230     <pre caption="Invoking menuconfig">
231     # <i>cd /usr/src/linux</i>
232     # <i>make menuconfig</i>
233     </pre>
234    
235     <p>
236 swift 1.4 Select the options required for your hardware and operating environment. For
237     additional information on kernel configuration, refer to the chapter entitled
238     <e>Configuring the Kernel</e> of the <uri
239     link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
240 swift 1.1 </p>
241    
242     <p>
243     Next, compile your kernel and copy it over to your boot partition. Again,
244 swift 1.4 follow the <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
245     instructions outlined in the chapter on <e>Configuring the Bootloader</e>. If
246     <path>/boot</path> is a separate partition, ensure it is mounted before copying
247     the compiled kernel to this directory! Failing to do so would keep you from
248     booting the system with your new kernel.
249 swift 1.1 </p>
250    
251     <pre caption="Compiling and installing the new kernel">
252     # <i>make &amp;&amp; make modules_install</i>
253     # <i>mount /boot</i>
254 swift 1.20 # <i>cp arch/i386/boot/bzImage /boot/bzImage-2.6.39-gentoo-r3</i>
255 swift 1.1 </pre>
256    
257     <p>
258 swift 1.18 Finally, you should update your boot loader configuration, adding an entry for
259 swift 1.5 the new kernel (don't delete the old one just yet!) and unmount the
260 swift 1.18 <path>/boot</path> partition. Again, refer to the
261 swift 1.4 <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
262     for detailed instructions on this procedure.
263 swift 1.1 </p>
264    
265     </body>
266     </section>
267     </chapter>
268    
269     <chapter>
270     <title>Reinstalling external modules</title>
271     <section>
272     <body>
273    
274     <p>
275     If you use any kernel modules that are not included in the kernel source tree
276 neysx 1.13 but are provided elsewhere in Portage (e.g. ALSA drivers and NVIDIA or ATI
277     graphics drivers), then you must reinstall these after upgrading the kernel.
278     This is as simple as re-merging the packages involved. For more information,
279     refer to the chapter on <e>Configuring the Kernel</e> in the <uri
280 nightmorph 1.14 link="/doc/en/handbook/">Gentoo Handbook</uri>.
281 swift 1.1 </p>
282    
283 swift 1.11 <p>
284     We provide you with an easy tool (<c>sys-kernel/module-rebuild</c>) which
285 nightmorph 1.14 rebuilds all the kernel modules you have installed using separate ebuilds for
286     the kernel at <path>/usr/src/linux</path>. Its use is straightforward. After
287     emerging it, simply run <c>module-rebuild populate</c> to populate the
288     database with a list of packages that will need to be rebuilt after upgrading
289     the kernel. Once you have finished upgrading or recompiling your kernel, run
290     <c>module-rebuild rebuild</c> to rebuild the drivers for your new kernel.
291 neysx 1.13 </p>
292    
293     <p>
294     For more information, run <c>module-rebuild</c> without any options to see a
295     list of commands that can be passed to the utility.
296 swift 1.11 </p>
297    
298 swift 1.1 </body>
299     </section>
300     </chapter>
301    
302     <chapter>
303 swift 1.20 <title>Updating your module configuration</title>
304     <section>
305     <body>
306    
307     <p>
308     If you have put specific module configuration entries in
309     <path>/etc/conf.d/modules</path>, then you might need to update the entries
310     accordingly.
311     </p>
312    
313     <pre caption="Sample /etc/conf.d/modules file">
314     <comment># The following will only auto-load the ieee1394 module in 2.6.38-gentoo-r6 kernels</comment>
315     modules_2_6_38_gentoo_r6="ieee1394"
316    
317     <comment># To support auto-loading on all possible versions, drop any reference to versions:</comment>
318     modules="ohci1394"
319     </pre>
320    
321     </body>
322     </section>
323     </chapter>
324    
325     <chapter>
326 swift 1.1 <title>Rebooting into the new kernel</title>
327     <section>
328     <body>
329    
330     <p>
331     Next, close all applications and reboot your system. If you followed the above
332 swift 1.5 instructions correctly, the boot loader menu should include an entry for the
333 swift 1.4 new kernel. Select the new kernel and let the system boot.
334 swift 1.1 </p>
335    
336     <p>
337 swift 1.4 Hopefully, your system successfully boots with the new kernel, and you can log
338     in to resume whatever you were doing. If this is the case, then the upgrade is
339     complete.
340 swift 1.1 </p>
341 neysx 1.13
342 swift 1.1 <p>
343 swift 1.18 If you made a mistake and the system fails to boot with the new kernel, reboot
344     the system and select the entry from the boot loader that corresponds to the
345 swift 1.4 last known working kernel. You can then restart from the <uri link="#install">
346 swift 1.18 Configuring, compiling, and installing the new kernel</uri> stage -- making
347     the appropriate changes to correct your mistake. In some cases, you might not
348     even need to reboot to do this (e.g. you missed a driver for an audio device,
349 swift 1.5 Ethernet adapter, etc.)
350 swift 1.1 </p>
351    
352     </body>
353     </section>
354     </chapter>
355    
356     <chapter>
357     <title>Running multiple kernels</title>
358     <section>
359     <body>
360    
361     <p>
362     You may have noticed, that when installing the sources for your newer kernel,
363 swift 1.4 the sources for your existing kernel were not removed. This is by design -- it
364 swift 1.1 allows you to easily switch between running different kernels.
365     </p>
366    
367     <p>
368     Switching between multiple kernels is as simple as leaving the kernel sources
369 swift 1.18 under <path>/usr/src/</path> and leaving the <path>bzImage</path> binaries on
370     your <path>/boot</path> partition (referenced by entries in your boot loader
371     configuration). Every time you boot up, you will be presented with a choice of
372 swift 1.5 which kernel to boot into.
373 swift 1.1 </p>
374    
375     </body>
376     </section>
377     </chapter>
378    
379     <chapter>
380     <title>Removing older kernels</title>
381     <section>
382     <body>
383    
384     <p>
385     Continuing on from the last section, you may be happy with your new kernel and
386     not have any need to keep older kernel versions around. To easily remove all
387     sources for a particular kernel except for the newest one, you can take
388 swift 1.4 advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
389     the example using <c>gentoo-sources</c>:
390 swift 1.1 </p>
391    
392     <pre caption="Pruning old versions">
393 neysx 1.3 # <i>emerge -P gentoo-sources</i>
394 swift 1.1 </pre>
395    
396     <p>
397     In most cases, temporary files used during compilation will still remain under
398 swift 1.18 the appropriate source directory under <path>/usr/src</path>. It is safe to
399 swift 1.1 remove these using <c>rm</c>.
400     </p>
401    
402     <p>
403     You can also safely delete any modules that were used by this kernel. This can
404     be done by removing the appropriate directories under <path>/lib/modules/</path>
405     that relate to the kernel versions you are removing. Be careful not to delete
406     modules belonging to kernels that you still use!
407     </p>
408    
409     <p>
410 swift 1.18 Finally, you can mount your <path>/boot</path> partition and remove the
411 jkt 1.10 <path>bzImage</path> file(s) for the kernel(s) you are pruning. You should also
412     edit your boot loader configuration so that it no longer references such
413     kernel(s).
414 swift 1.1 </p>
415    
416     </body>
417     </section>
418     </chapter>
419    
420     <chapter>
421 neysx 1.3 <title>Advanced: Using your old kernel .config to configure a new one</title>
422     <section>
423     <body>
424    
425     <p>
426     It is sometimes possible to save time by re-using the configuration file from
427     your old kernel when configuring the new one. Note that this is generally
428 swift 1.4 unsafe -- too many changes between every kernel release for this to be a
429 neysx 1.3 reliable upgrade path.
430     </p>
431    
432     <p>
433     The only situation where this is appropriate is when upgrading from one Gentoo
434     kernel revision to another. For example, the changes made between
435     <c>gentoo-sources-2.6.9-r1</c> and <c>gentoo-sources-2.6.9-r2</c> will be very
436     small, so it is usually OK to use the following method. However, it is not
437     appropriate to use it in the example used throughout this document: upgrading
438     from 2.6.8 to 2.6.9. Too many changes between the official releases, and the
439     method described below does not display enough context to the user, often
440     resulting in the user running into problems because they disabled options that
441     they really didn't want to.
442     </p>
443    
444     <p>
445 neysx 1.16 To reuse your old <path>.config</path>, you simply need to copy it over and
446     then run <c>make oldconfig</c>. In the following example, we take the
447     configuration from <c>gentoo-sources-2.6.9-r1</c> and import it into
448 neysx 1.3 <c>gentoo-sources-2.6.9-r2</c>.
449     </p>
450    
451     <pre caption="Reusing your old config">
452     # <i>cd /usr/src/linux-2.6.9-gentoo-r2</i>
453     # <i>cp ../linux-2.6.9-gentoo-r1/.config .</i>
454     # <i>make oldconfig</i>
455     </pre>
456    
457 neysx 1.16 <pre caption="Reusing your old config with genkernel">
458     # <i>cd /etc/kernels</i>
459     # <i>cp kernel-config-x86-2.6.9-gentoo-r1 kernel-config-x86-2.6.9-gentoo-r2</i>
460     # <i>genkernel all</i>
461     </pre>
462    
463 neysx 1.3 <p>
464     At this point, you may be asked to produce answers for configuration options
465     which have changed between the two versions. Once you have done that, you can
466     compile and install your kernel as normal, without having to go through the
467     <c>menuconfig</c> configuration process.
468     </p>
469    
470 nightmorph 1.17 <p>
471     A much safer upgrading method is to copy your config as previously shown, and
472     then simply run <c>make menuconfig</c>. This avoids the problems of <c>make
473     oldconfig</c> mentioned previously, as <c>make menuconfig</c> will load up your
474     previous configuration as much as possible into the menu. Now all you have to
475     do is go through each option and look for new sections, removals, and so on. By
476     using <c>menuconfig</c>, you gain context for all the new changes, and can
477     easily view the new choices and review help screens much easier. You can even
478     use this for upgrades such as 2.6.8 to 2.6.9; just make sure you read through
479     the options carefully. Once you've finished, compile and install your kernel as
480     normal.
481     </p>
482    
483 neysx 1.3 </body>
484     </section>
485     </chapter>
486    
487     <chapter>
488 swift 1.1 <title>Problems after a kernel upgrade?</title>
489     <section>
490     <body>
491    
492     <p>
493     With the rapid development of the Linux kernel, it is inevitable that some
494 neysx 1.3 changes made from one kernel release to another may cause some problems. If you
495     have any issues with the latest versions of <uri
496     link="/doc/en/gentoo-kernel.xml#doc_chap2"> Gentoo-supported kernels</uri> then
497     please do report the issues to us.
498 swift 1.1 </p>
499    
500     </body>
501     </section>
502     </chapter>
503    
504     </guide>

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