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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 1.1 2004/11/02 09:36:23 swift Exp $ -->
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<!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
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<guide link="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/2.0 -->
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<license/>
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<version>0.1.1</version>
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<date>2004-12-06</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 targetted 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-dev-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 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. Reasons for upgrading kernel are generally either to take
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advantage of a specific new feature or driver, to be protected against a
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security vulnerability, or just to maintain an up-to-date and healthy 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 U ] sys-kernel/gentoo-dev-sources-2.6.9-r2 [2.6.8-r5]
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</pre>
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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-dev-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, my 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 you to maintain a symbolic link, located at
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<path>/usr/src/linux</path>. This should point to the sources of the
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kernel you are running.
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</p>
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<p>
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In this case, we need to update the symbolic link to point at the kernel
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sources that we are about to upgrade to. Continuing our example:
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</p>
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<pre caption="Updating the /usr/src/linux softlink">
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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="http://www.gentoo.org/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>. A quick summary is provided here.
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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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# <i>genkernel 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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bootloader config, 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="http://www.gentoo.org/doc/en/genkernel.xml">Gentoo Linux Genkernel
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Guide</uri>, or refer to the handbook.
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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. Refer
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to the <e>Gentoo Handbook</e> for additional guidance on this.
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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 handbook instructions here, but don't forget to mount your /boot
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partition first! In the initial installation, you would have already mounted
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this at a much earlier stage.
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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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# <i>cp System.map /boot/System.map-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 bootloader config, adding an entry for the
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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 handbook for instructions
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here.
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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 on every kernel upgrade. This is as simple as
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re-merging the packages involved. Refer again to the
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<uri link="http://www.gentoo.org/doc/en/handbook/index.xml">Gentoo
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Handbook</uri> <e>Configuring the Kernel</e> chapter for more info here.
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Re-merging these packages will ensure they build against the source tree at
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<path>/usr/src/linux</path> - therefore they will actually being installed
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for the kernel we just compiled.
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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, you will see an entry for your new kernel on your
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bootloader. 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 will boot without problem and you can log in and start
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working as usual. If everything is working, then the upgrade is complete at
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this stage.
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</p>
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<p>
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If you have made a mistake and your system will not boot into the new kernel,
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then you can simply reboot and boot into your previous working kernel. You can
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then restart from the <uri link="#install">Configuring, compiling, and
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installing the new kernel</uri> stage - making the appropriate changes to
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correct your mistake. In some cases (e.g. you just missed a network driver)
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then you might not even need to reboot to do this.
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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 and
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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 bootloader
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config). Every time you boot up, you will be presented with a choice of which
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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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advantages of emerge's <e>prune</e> option. Continuing the example using
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gentoo-dev-sources:
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</p>
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<pre caption="Pruning old versions">
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# <i>emerge -P gentoo-dev-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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<p>
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Finally, you can mount your <path>/boot</path> partition and remove the
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<path>bzImage</path> and <path>System.map</path> files for the kernel(s)
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you are pruning. You should also edit your bootloader config so that it
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no longer references this 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>Problems after a kernel upgrade?</title>
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<section>
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<body>
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<p>
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With the rapid development of the Linux kernel, it is inevitable that some
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changes made from one kernel release to another may cause some problems. If
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you have any issues with the latest versions of
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<uri link="http://www.gentoo.org/doc/en/gentoo-kernel.xml#doc_chap2">
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Gentoo-supported kernels</uri> then please do report the issues to us.
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</p>
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</body>
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</section>
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</chapter>
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</guide>
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