doc/en/kernel-upgrade.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/kernel-upgrade.xml,v 1.14 2006/02/22 20:30:20 nightmorph Exp $ -->

<!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
<guide link="/doc/en/kernel-upgrade.xml">
<title>Gentoo Linux Kernel Upgrade Guide</title>
<author title="Author">
  <mail link="dsd@gentoo.org">Daniel Drake</mail>
</author>

<abstract>
This document describes the process of upgrading your kernel from one release
to another.
</abstract>

<!-- The content of this document is licensed under the CC-BY-SA license -->
<!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
<license/>

<version>0.4</version>
<date>2006-05-04</date>

<chapter>
<title>Introduction</title>
<section>
<body>

<p>
The kernel is one of the few package classes in portage that requires some
manual intervention to complete the upgrade. Portage will download and
install the kernel source for you, but then it is up to you to step in and
compile the new kernel before any changes will take effect.
</p>

<p>
Although this guide is targeted at users upgrading from one kernel release
to another, it will also be useful for users migrating from one kernel
package to another.
</p>

<p>
<c>gentoo-sources</c> is used as an example in this document, however, the
instructions here also apply to the other packages present in our tree.
</p>

</body>
</section>
</chapter>

<chapter>
<title>Why upgrade the kernel?</title>
<section>
<body>

<p>
Generally, upgrading from one minor kernel release to the next won't bring any
major differences. There are several reasons to upgrade the kernel. One is to
take advantage of a specific new feature or driver; another is to be protected 
against a security vulnerability, or just to maintain an up-to-date and healthy 
system.
</p>

<p>
Even if you choose not to update to every new kernel revision, it is
recommended that you at least upgrade from time to time. It is strongly
recommended that you immediately upgrade to a new kernel if that new release
solves a security problem.
</p>

</body>
</section>
</chapter>

<chapter>
<title>Obtaining the newer sources through Portage</title>
<section>
<body>

<p>
You upgrade the kernel sources like you would upgrade any other package -
using the <c>emerge</c> utility. It will probably be the case that you want to
upgrade your kernel when you see the upgrade appearing on your world updates
list. For example:
</p>

<pre caption="New kernel sources appearing on update list">
# <i>emerge -Dup world</i>
Calculating dependencies ...done!
[ebuild    NS ] sys-kernel/gentoo-sources-2.6.9-r2 [2.6.8-r5]
</pre>

<note>
The "NS" label in the above output means that the new kernel will be installed
in a New Slot, i.e. the sources of your old kernel will be kept around, until
you manually remove them.
</note>

<p>
You can then go ahead and install the update, e.g.:
</p>

<pre caption="Upgrading your kernel sources">
# <i>emerge -u gentoo-sources</i>
</pre>

<p>
The kernel sources will then be installed into a subdirectory of 
<path>/usr/src</path>. In the above example, the new kernel sources will be 
installed at <path>/usr/src/linux-2.6.9-gentoo-r2</path>.
</p>

</body>
</section>
</chapter>

<chapter>
<title>Updating the /usr/src/linux symbolic link</title>
<section>
<body>

<p>
Gentoo requires that the <path>/usr/src/linux</path> symbolic link points to
the sources of the kernel you are running.
</p>

<p>
Portage can update the symlink automatically when you emerge new kernel
sources. All you have to do is add the <c>symlink</c> flag to the USE variable
in <path>/etc/make.conf</path>.
</p>

<pre caption="Example of USE variable in /etc/make.conf">
<comment>(Add the symlink keyword)</comment>
USE="<i>symlink</i> x86 3dnow 3dnowex X aac aalib adns alsa apache2"
</pre>

<p>
Alternatively, you could use <c>app-admin/eselect</c> to modify the symlink.
</p>

<pre caption="Using eselect to symlink">
<comment>(Install eselect if you don't have it)</comment>
# <i>emerge eselect</i>
<comment>(See the list of available kernels)</comment>
# <i>eselect kernel list</i>
Available kernel symlink targets:
  [1]   linux-2.6.9-gentoo-r1
  [2]   linux-2.6.9-gentoo-r2
<comment>(Select the correct kernel)</comment>
# <i>eselect kernel set 1</i>
</pre>

<p>
If you really want to do it yourself, the following example shows you how to
make the link point to <path>linux-2.6.9-gentoo-r2</path>:
</p>

<pre caption="Updating the /usr/src/linux softlink manually">
# <i>cd /usr/src</i>
# <i>ln -sfn linux-2.6.9-gentoo-r2 linux</i>
</pre>

</body>
</section>
</chapter>

<chapter id="install">
<title>Configuring, compiling and installing the new kernel</title>
<section>
<body>

<p>
For either of these options, you should refer to the instructions given in the
<uri link="/doc/en/handbook/index.xml">Gentoo
Handbook</uri> relating to <e>Configuring the Kernel</e> and <e>Configuring
the Bootloader</e>. Below is an outline of the required actions:
</p>

</body>
</section>
<section>
<title>Option 1: Automatic kernel setup with Genkernel</title>
<body>

<p>
If you are a genkernel user, you just need to repeat the stages you went
through when installing your kernel for the first time.
</p>

<p>
Simply run genkernel in the normal way:
</p>

<pre caption="Invoking genkernel">
<comment>(For 2.4 kernels:)</comment>
# <i>genkernel all</i>

<comment>(For 2.6 kernels:)</comment>
# <i>genkernel --udev all</i>
</pre>

<p>
You can also use extra parameters for other genkernel functionality. For
example, if you wish to configure some extra kernel options using
<c>menuconfig</c> and you wish genkernel to automatically update your grub
boot loader configuration, then invoke genkernel as follows:
</p>

<pre caption="Invoking genkernel with some common arguments">
# <i>genkernel --menuconfig --bootloader=grub all</i>
</pre>

<p>
For more info, follow the
<uri link="/doc/en/genkernel.xml">Gentoo Linux Genkernel
Guide</uri>, or refer to the <uri link="/doc/en/handbook/index.xml">Gentoo
Handbook</uri>. Many of the options can be set in the configuration file for
<c>genkernel</c>, <path>/etc/genkernel.conf</path>.
</p>

</body>
</section>
<section>
<title>Option 2: Manual configuration</title>
<body>

<p>
To begin, open the <c>menuconfig</c> utility in the kernel source tree:
</p>

<pre caption="Invoking menuconfig">
# <i>cd /usr/src/linux</i>
# <i>make menuconfig</i>
</pre>

<p>
Select the options required for your hardware and operating environment. For
additional information on kernel configuration, refer to the chapter entitled
<e>Configuring the Kernel</e> of the <uri
link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
</p>

<p>
Next, compile your kernel and copy it over to your boot partition. Again,
follow the <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
instructions outlined in the chapter on <e>Configuring the Bootloader</e>. If
<path>/boot</path> is a separate partition, ensure it is mounted before copying
the compiled kernel to this directory! Failing to do so would keep you from
booting the system with your new kernel.
</p>

<pre caption="Compiling and installing the new kernel">
# <i>make &amp;&amp; make modules_install</i>
# <i>mount /boot</i>
# <i>cp arch/i386/boot/bzImage /boot/bzImage-2.6.9-gentoo-r2</i>
</pre>

<p>
Finally, you should update your boot loader configuration, adding an entry for 
the new kernel (don't delete the old one just yet!) and unmount the
<path>/boot</path> partition. Again, refer to the 
<uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
for detailed instructions on this procedure.
</p>

</body>
</section>
</chapter>

<chapter>
<title>Reinstalling external modules</title>
<section>
<body>

<p>
If you use any kernel modules that are not included in the kernel source tree
but are provided elsewhere in Portage (e.g. ALSA drivers and NVIDIA or ATI
graphics drivers), then you must reinstall these after upgrading the kernel.
This is as simple as re-merging the packages involved. For more information,
refer to the chapter on <e>Configuring the Kernel</e> in the <uri
link="/doc/en/handbook/">Gentoo Handbook</uri>.
</p>

<p>
We provide you with an easy tool (<c>sys-kernel/module-rebuild</c>) which
rebuilds all the kernel modules you have installed using separate ebuilds for
the kernel at <path>/usr/src/linux</path>. Its use is straightforward. After
emerging it, simply run <c>module-rebuild populate</c> to populate the
database with a list of packages that will need to be rebuilt after upgrading
the kernel. Once you have finished upgrading or recompiling your kernel, run
<c>module-rebuild rebuild</c> to rebuild the drivers for your new kernel.
</p>

<p>
For more information, run <c>module-rebuild</c> without any options to see a
list of commands that can be passed to the utility.
</p>

</body>
</section>
</chapter>

<chapter>
<title>Rebooting into the new kernel</title>
<section>
<body>

<p>
Next, close all applications and reboot your system. If you followed the above
instructions correctly, the boot loader menu should include an entry for the
new kernel. Select the new kernel and let the system boot.
</p>

<p>
Hopefully, your system successfully boots with the new kernel, and you can log
in to resume whatever you were doing. If this is the case, then the upgrade is
complete.
</p>

<p>
If you made a mistake and the system fails to boot with the new kernel, reboot 
the system and select the entry from the boot loader that corresponds to the 
last known working kernel. You can then restart from the <uri link="#install">
Configuring, compiling, and installing the new kernel</uri> stage -- making 
the appropriate changes to correct your mistake. In some cases, you might not 
even need to reboot to do this (e.g. you missed a driver for an audio device, 
Ethernet adapter, etc.)
</p>

</body>
</section>
</chapter>

<chapter>
<title>Running multiple kernels</title>
<section>
<body>

<p>
You may have noticed, that when installing the sources for your newer kernel,
the sources for your existing kernel were not removed. This is by design -- it
allows you to easily switch between running different kernels.
</p>

<p>
Switching between multiple kernels is as simple as leaving the kernel sources
under <path>/usr/src/</path> and leaving the <path>bzImage</path> binaries on 
your <path>/boot</path> partition (referenced by entries in your boot loader 
configuration). Every time you boot up, you will be presented with a choice of 
which kernel to boot into.
</p>

</body>
</section>
</chapter>

<chapter>
<title>Removing older kernels</title>
<section>
<body>

<p>
Continuing on from the last section, you may be happy with your new kernel and
not have any need to keep older kernel versions around. To easily remove all
sources for a particular kernel except for the newest one, you can take
advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
the example using <c>gentoo-sources</c>:
</p>

<pre caption="Pruning old versions">
# <i>emerge -P gentoo-sources</i>
</pre>

<p>
In most cases, temporary files used during compilation will still remain under
the appropriate source directory under <path>/usr/src</path>. It is safe to 
remove these using <c>rm</c>.
</p>

<p>
You can also safely delete any modules that were used by this kernel. This can
be done by removing the appropriate directories under <path>/lib/modules/</path>
that relate to the kernel versions you are removing. Be careful not to delete
modules belonging to kernels that you still use!
</p>

<p>
Finally, you can mount your <path>/boot</path> partition and remove the 
<path>bzImage</path> file(s) for the kernel(s) you are pruning. You should also
edit your boot loader configuration so that it no longer references such
kernel(s).
</p>

</body>
</section>
</chapter>

<chapter>
<title>Advanced: Using your old kernel .config to configure a new one</title>
<section>
<body>

<p>
It is sometimes possible to save time by re-using the configuration file from
your old kernel when configuring the new one. Note that this is generally
unsafe -- too many changes between every kernel release for this to be a
reliable upgrade path.
</p>

<p>
The only situation where this is appropriate is when upgrading from one Gentoo
kernel revision to another. For example, the changes made between
<c>gentoo-sources-2.6.9-r1</c> and <c>gentoo-sources-2.6.9-r2</c> will be very
small, so it is usually OK to use the following method. However, it is not
appropriate to use it in the example used throughout this document: upgrading
from 2.6.8 to 2.6.9. Too many changes between the official releases, and the
method described below does not display enough context to the user, often
resulting in the user running into problems because they disabled options that
they really didn't want to.
</p>

<p>
To reuse your old <path>.config</path>, you simply need to copy it over and then
run <c>make oldconfig</c>. In the following example, we take the configuration 
from <c>gentoo-sources-2.6.9-r1</c> and import it into 
<c>gentoo-sources-2.6.9-r2</c>.
</p>

<pre caption="Reusing your old config">
# <i>cd /usr/src/linux-2.6.9-gentoo-r2</i>
# <i>cp ../linux-2.6.9-gentoo-r1/.config .</i>
# <i>make oldconfig</i>
</pre>

<p>
At this point, you may be asked to produce answers for configuration options
which have changed between the two versions. Once you have done that, you can
compile and install your kernel as normal, without having to go through the
<c>menuconfig</c> configuration process.
</p>

</body>
</section>
</chapter>

<chapter>
<title>Problems after a kernel upgrade?</title>
<section>
<body>

<p>
With the rapid development of the Linux kernel, it is inevitable that some
changes made from one kernel release to another may cause some problems. If you
have any issues with the latest versions of <uri
link="/doc/en/gentoo-kernel.xml#doc_chap2"> Gentoo-supported kernels</uri> then
please do report the issues to us.
</p>

</body>
</section>
</chapter>

</guide>
1	swift	1.1	<?xml version="1.0" encoding="UTF-8"?>
2	fox2mike	1.15	<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/kernel-upgrade.xml,v 1.14 2006/02/22 20:30:20 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	fox2mike	1.15	<version>0.4</version>
21			<date>2006-05-04</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			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	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	neysx	1.3	[ebuild NS ] sys-kernel/gentoo-sources-2.6.9-r2 [2.6.8-r5]
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			The kernel sources will then be installed into a subdirectory of
108	swift	1.4	<path>/usr/src</path>. In the above example, the new kernel sources will be
109	swift	1.1	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	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			[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	neysx	1.8	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	swift	1.1	# <i>cd /usr/src</i>
160	swift	1.2	# <i>ln -sfn linux-2.6.9-gentoo-r2 linux</i>
161	swift	1.1	</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	swift	1.6	<uri link="/doc/en/handbook/index.xml">Gentoo
175	swift	1.1	Handbook</uri> relating to <e>Configuring the Kernel</e> and <e>Configuring
176	swift	1.4	the Bootloader</e>. Below is an outline of the required actions:
177	swift	1.1	</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	swift	1.7	<comment>(For 2.4 kernels:)</comment>
196	swift	1.1	# <i>genkernel all</i>
197	swift	1.7
198			<comment>(For 2.6 kernels:)</comment>
199			# <i>genkernel --udev all</i>
200	swift	1.1	</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	swift	1.5	boot 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			For more info, follow the
215	swift	1.6	<uri link="/doc/en/genkernel.xml">Gentoo Linux Genkernel
216	swift	1.4	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	swift	1.6	<c>genkernel</c>, <path>/etc/genkernel.conf</path>.
219	swift	1.1	</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	swift	1.4	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	swift	1.1	</p>
242
243			<p>
244			Next, compile your kernel and copy it over to your boot partition. Again,
245	swift	1.4	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	swift	1.1	</p>
251
252			<pre caption="Compiling and installing the new kernel">
253			# <i>make && 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	swift	1.5	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	swift	1.4	<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	swift	1.1	</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	neysx	1.13	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	nightmorph	1.14	link="/doc/en/handbook/">Gentoo Handbook</uri>.
282	swift	1.1	</p>
283
284	swift	1.11	<p>
285			We provide you with an easy tool (<c>sys-kernel/module-rebuild</c>) which
286	nightmorph	1.14	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	neysx	1.13	</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	swift	1.11	</p>
298
299	swift	1.1	</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	swift	1.5	instructions correctly, the boot loader menu should include an entry for the
311	swift	1.4	new kernel. Select the new kernel and let the system boot.
312	swift	1.1	</p>
313
314			<p>
315	swift	1.4	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	swift	1.1	</p>
319	neysx	1.13
320	swift	1.1	<p>
321	swift	1.4	If you made a mistake and the system fails to boot with the new kernel, reboot
322	swift	1.5	the system and select the entry from the boot loader that corresponds to the
323	swift	1.4	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	swift	1.5	Ethernet adapter, etc.)
328	swift	1.1	</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	swift	1.4	the sources for your existing kernel were not removed. This is by design -- it
342	swift	1.1	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	swift	1.5	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	swift	1.1	</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	swift	1.4	advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
367			the example using <c>gentoo-sources</c>:
368	swift	1.1	</p>
369
370			<pre caption="Pruning old versions">
371	neysx	1.3	# <i>emerge -P gentoo-sources</i>
372	swift	1.1	</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	jkt	1.10	<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	swift	1.1	</p>
393
394			</body>
395			</section>
396			</chapter>
397
398			<chapter>
399	neysx	1.3	<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	swift	1.4	unsafe -- too many changes between every kernel release for this to be a
407	neysx	1.3	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	swift	1.5	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	neysx	1.3	<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	swift	1.1	<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	neysx	1.3	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	swift	1.1	</p>
458
459			</body>
460			</section>
461			</chapter>
462
463			</guide>