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<?xml version="1.0" encoding="UTF-8"?>
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<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/kernel-upgrade.xml,v 1.9 2005/10/06 19:13:03 jkt Exp $ -->
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<!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
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<guide link="/doc/en/kernel-upgrade.xml">
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<title>Gentoo Linux Kernel Upgrade Guide</title>
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<author title="Author">
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<mail link="dsd@gentoo.org">Daniel Drake</mail>
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</author>
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<abstract>
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This document describes the process of upgrading your kernel from one release
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to another.
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</abstract>
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<!-- The content of this document is licensed under the CC-BY-SA license -->
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<!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
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<license/>
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<version>0.1.7</version>
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<date>2005-10-06</date>
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<chapter>
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<title>Introduction</title>
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<section>
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<body>
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<p>
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The kernel is one of the few package classes in portage that requires some
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manual intervention to complete the upgrade. Portage will download and
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install the kernel source for you, but then it is up to you to step in and
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compile the new kernel before any changes will take effect.
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</p>
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<p>
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Although this guide is targeted at users upgrading from one kernel release
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to another, it will also be useful for users migrating from one kernel
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package to another.
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</p>
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<p>
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<c>gentoo-sources</c> is used as an example in this document, however, the
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instructions here also apply to the other packages present in our tree.
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Why upgrade the kernel?</title>
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<section>
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<body>
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<p>
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Generally, upgrading from one minor kernel release to the next won't bring any
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major differences. There are several reasons to upgrade the kernel. One is to
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take advantage of a specific new feature or driver; another is to be protected
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against a security vulnerability, or just to maintain an up-to-date and healthy
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system.
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</p>
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<p>
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Even if you choose not to update to every new kernel revision, it is
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recommended that you at least upgrade from time to time. It is strongly
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recommended that you immediately upgrade to a new kernel if that new release
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solves a security problem.
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Obtaining the newer sources through Portage</title>
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<section>
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<body>
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<p>
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You upgrade the kernel sources like you would upgrade any other package -
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using the <c>emerge</c> utility. It will probably be the case that you want to
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upgrade your kernel when you see the upgrade appearing on your world updates
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list. For example:
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</p>
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<pre caption="New kernel sources appearing on update list">
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# <i>emerge -Dup world</i>
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Calculating dependencies ...done!
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[ebuild NS ] sys-kernel/gentoo-sources-2.6.9-r2 [2.6.8-r5]
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</pre>
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<note>
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The "NS" label in the above output means that the new kernel will be installed
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in a New Slot, i.e. the sources of your old kernel will be kept around, until
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you manually remove them.
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</note>
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<p>
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You can then go ahead and install the update, e.g.:
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</p>
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<pre caption="Upgrading your kernel sources">
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# <i>emerge -u gentoo-sources</i>
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</pre>
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<p>
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The kernel sources will then be installed into a subdirectory of
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<path>/usr/src</path>. In the above example, the new kernel sources will be
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installed at <path>/usr/src/linux-2.6.9-gentoo-r2</path>.
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Updating the /usr/src/linux symbolic link</title>
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<section>
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<body>
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<p>
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Gentoo requires that the <path>/usr/src/linux</path> symbolic link points to
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the sources of the kernel you are running.
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</p>
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<p>
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Portage can update the symlink automatically when you emerge new kernel
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sources. All you have to do is add the <c>symlink</c> flag to the USE variable
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in <path>/etc/make.conf</path>.
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</p>
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<pre caption="Example of USE variable in /etc/make.conf">
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<comment>(Add the symlink keyword)</comment>
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USE="<i>symlink</i> x86 3dnow 3dnowex X aac aalib adns alsa apache2"
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</pre>
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<p>
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If you really want to do it yourself, the following example shows you how to
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make the link point to <path>linux-2.6.9-gentoo-r2</path>:
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</p>
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<pre caption="Updating the /usr/src/linux softlink manually">
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# <i>cd /usr/src</i>
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# <i>ln -sfn linux-2.6.9-gentoo-r2 linux</i>
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</pre>
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</body>
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</section>
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</chapter>
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<chapter id="install">
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<title>Configuring, compiling and installing the new kernel</title>
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<section>
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<body>
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<p>
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For either of these options, you should refer to the instructions given in the
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<uri link="/doc/en/handbook/index.xml">Gentoo
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Handbook</uri> relating to <e>Configuring the Kernel</e> and <e>Configuring
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the Bootloader</e>. Below is an outline of the required actions:
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</p>
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</body>
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</section>
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<section>
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<title>Option 1: Automatic kernel setup with Genkernel</title>
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<body>
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<p>
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If you are a genkernel user, you just need to repeat the stages you went
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through when installing your kernel for the first time.
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</p>
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<p>
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Simply run genkernel in the normal way:
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</p>
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<pre caption="Invoking genkernel">
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<comment>(For 2.4 kernels:)</comment>
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# <i>genkernel all</i>
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<comment>(For 2.6 kernels:)</comment>
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# <i>genkernel --udev all</i>
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</pre>
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<p>
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You can also use extra parameters for other genkernel functionality. For
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example, if you wish to configure some extra kernel options using
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<c>menuconfig</c> and you wish genkernel to automatically update your grub
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boot loader configuration, then invoke genkernel as follows:
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</p>
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<pre caption="Invoking genkernel with some common arguments">
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# <i>genkernel --menuconfig --bootloader=grub all</i>
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</pre>
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<p>
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For more info, follow the
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<uri link="/doc/en/genkernel.xml">Gentoo Linux Genkernel
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Guide</uri>, or refer to the <uri link="/doc/en/handbook/index.xml">Gentoo
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Handbook</uri>. Many of the options can be set in the configuration file for
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<c>genkernel</c>, <path>/etc/genkernel.conf</path>.
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</p>
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</body>
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</section>
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<section>
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<title>Option 2: Manual configuration</title>
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<body>
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<p>
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To begin, open the <c>menuconfig</c> utility in the kernel source tree:
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</p>
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<pre caption="Invoking menuconfig">
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# <i>cd /usr/src/linux</i>
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# <i>make menuconfig</i>
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</pre>
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<p>
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Select the options required for your hardware and operating environment. For
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additional information on kernel configuration, refer to the chapter entitled
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<e>Configuring the Kernel</e> of the <uri
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link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
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</p>
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<p>
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Next, compile your kernel and copy it over to your boot partition. Again,
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follow the <uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
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instructions outlined in the chapter on <e>Configuring the Bootloader</e>. If
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<path>/boot</path> is a separate partition, ensure it is mounted before copying
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the compiled kernel to this directory! Failing to do so would keep you from
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booting the system with your new kernel.
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</p>
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<pre caption="Compiling and installing the new kernel">
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# <i>make && make modules_install</i>
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# <i>mount /boot</i>
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# <i>cp arch/i386/boot/bzImage /boot/bzImage-2.6.9-gentoo-r2</i>
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</pre>
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<p>
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Finally, you should update your boot loader configuration, adding an entry for
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the new kernel (don't delete the old one just yet!) and unmount the
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<path>/boot</path> partition. Again, refer to the
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<uri link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>
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for detailed instructions on this procedure.
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Reinstalling external modules</title>
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<section>
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<body>
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<p>
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If you use any kernel modules that are not included in the kernel source tree
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but are provided elsewhere in portage (e.g. NVIDIA or ATI graphics drivers),
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then you must reinstall these after upgrading the kernel. This is as simple as
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re-merging the packages involved. For more information, refer to the chapter on
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<e>Configuring the Kernel</e> in the <uri
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link="/doc/en/handbook/index.xml">Gentoo Handbook</uri>.
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To ensure these packages will build against the source tree at
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<path>/usr/src/linux</path>, first uninstall the packages, then re-emerge them.
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If old sources for these packages are kept by portage, this uninstall/re-emerge
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procedure will make sure that they are rebuilt to work with the new kernel.
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Rebooting into the new kernel</title>
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<section>
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<body>
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<p>
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Next, close all applications and reboot your system. If you followed the above
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instructions correctly, the boot loader menu should include an entry for the
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new kernel. Select the new kernel and let the system boot.
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</p>
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<p>
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Hopefully, your system successfully boots with the new kernel, and you can log
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in to resume whatever you were doing. If this is the case, then the upgrade is
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complete.
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</p>
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<p>
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If you made a mistake and the system fails to boot with the new kernel, reboot
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the system and select the entry from the boot loader that corresponds to the
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last known working kernel. You can then restart from the <uri link="#install">
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Configuring, compiling, and installing the new kernel</uri> stage -- making
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the appropriate changes to correct your mistake. In some cases, you might not
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even need to reboot to do this (e.g. you missed a driver for an audio device,
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Ethernet adapter, etc.)
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Running multiple kernels</title>
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<section>
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<body>
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<p>
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You may have noticed, that when installing the sources for your newer kernel,
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the sources for your existing kernel were not removed. This is by design -- it
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allows you to easily switch between running different kernels.
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</p>
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<p>
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Switching between multiple kernels is as simple as leaving the kernel sources
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under <path>/usr/src/</path> and leaving the <path>bzImage</path> binaries on
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your <path>/boot</path> partition (referenced by entries in your boot loader
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configuration). Every time you boot up, you will be presented with a choice of
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which kernel to boot into.
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Removing older kernels</title>
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<section>
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<body>
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<p>
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Continuing on from the last section, you may be happy with your new kernel and
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not have any need to keep older kernel versions around. To easily remove all
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sources for a particular kernel except for the newest one, you can take
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advantage of the <e>prune</e> option available through <c>emerge</c>. Continuing
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the example using <c>gentoo-sources</c>:
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</p>
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<pre caption="Pruning old versions">
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# <i>emerge -P gentoo-sources</i>
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</pre>
|
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<p>
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In most cases, temporary files used during compilation will still remain under
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the appropriate source directory under <path>/usr/src</path>. It is safe to
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remove these using <c>rm</c>.
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</p>
|
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<p>
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You can also safely delete any modules that were used by this kernel. This can
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be done by removing the appropriate directories under <path>/lib/modules/</path>
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that relate to the kernel versions you are removing. Be careful not to delete
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modules belonging to kernels that you still use!
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</p>
|
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|
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<p>
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Finally, you can mount your <path>/boot</path> partition and remove the
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<path>bzImage</path> file(s) for the kernel(s) you are pruning. You should also
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edit your boot loader configuration so that it no longer references such
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kernel(s).
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</p>
|
| 366 |
|
| 367 |
</body>
|
| 368 |
</section>
|
| 369 |
</chapter>
|
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|
| 371 |
<chapter>
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<title>Advanced: Using your old kernel .config to configure a new one</title>
|
| 373 |
<section>
|
| 374 |
<body>
|
| 375 |
|
| 376 |
<p>
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| 377 |
It is sometimes possible to save time by re-using the configuration file from
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| 378 |
your old kernel when configuring the new one. Note that this is generally
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unsafe -- too many changes between every kernel release for this to be a
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reliable upgrade path.
|
| 381 |
</p>
|
| 382 |
|
| 383 |
<p>
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| 384 |
The only situation where this is appropriate is when upgrading from one Gentoo
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| 385 |
kernel revision to another. For example, the changes made between
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| 386 |
<c>gentoo-sources-2.6.9-r1</c> and <c>gentoo-sources-2.6.9-r2</c> will be very
|
| 387 |
small, so it is usually OK to use the following method. However, it is not
|
| 388 |
appropriate to use it in the example used throughout this document: upgrading
|
| 389 |
from 2.6.8 to 2.6.9. Too many changes between the official releases, and the
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| 390 |
method described below does not display enough context to the user, often
|
| 391 |
resulting in the user running into problems because they disabled options that
|
| 392 |
they really didn't want to.
|
| 393 |
</p>
|
| 394 |
|
| 395 |
<p>
|
| 396 |
To reuse your old <path>.config</path>, you simply need to copy it over and then
|
| 397 |
run <c>make oldconfig</c>. In the following example, we take the configuration
|
| 398 |
from <c>gentoo-sources-2.6.9-r1</c> and import it into
|
| 399 |
<c>gentoo-sources-2.6.9-r2</c>.
|
| 400 |
</p>
|
| 401 |
|
| 402 |
<pre caption="Reusing your old config">
|
| 403 |
# <i>cd /usr/src/linux-2.6.9-gentoo-r2</i>
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| 404 |
# <i>cp ../linux-2.6.9-gentoo-r1/.config .</i>
|
| 405 |
# <i>make oldconfig</i>
|
| 406 |
</pre>
|
| 407 |
|
| 408 |
<p>
|
| 409 |
At this point, you may be asked to produce answers for configuration options
|
| 410 |
which have changed between the two versions. Once you have done that, you can
|
| 411 |
compile and install your kernel as normal, without having to go through the
|
| 412 |
<c>menuconfig</c> configuration process.
|
| 413 |
</p>
|
| 414 |
|
| 415 |
</body>
|
| 416 |
</section>
|
| 417 |
</chapter>
|
| 418 |
|
| 419 |
<chapter>
|
| 420 |
<title>Problems after a kernel upgrade?</title>
|
| 421 |
<section>
|
| 422 |
<body>
|
| 423 |
|
| 424 |
<p>
|
| 425 |
With the rapid development of the Linux kernel, it is inevitable that some
|
| 426 |
changes made from one kernel release to another may cause some problems. If you
|
| 427 |
have any issues with the latest versions of <uri
|
| 428 |
link="/doc/en/gentoo-kernel.xml#doc_chap2"> Gentoo-supported kernels</uri> then
|
| 429 |
please do report the issues to us.
|
| 430 |
</p>
|
| 431 |
|
| 432 |
</body>
|
| 433 |
</section>
|
| 434 |
</chapter>
|
| 435 |
|
| 436 |
</guide>
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