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<!-- retain these comments for translator revision tracking -->
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<!-- $Id: kernel-baking.xml 11648 2004-03-22 00:37:46Z joeyh $ -->
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<sect1 id="kernel-baking"><title>Compiling a New Kernel</title>
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<para>
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Why would someone want to compile a new kernel? It is often not
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necessary since the default kernel shipped with Debian handles most
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configurations. However, it is useful to compile a new kernel in order
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to:
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<itemizedlist>
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<listitem><para>
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handle special hardware needs, or hardware conflicts with the pre-supplied
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kernels
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</para></listitem>
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<listitem><para>
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handle hardware or options not included in the stock kernel, such as
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APM or SMP
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</para></listitem>
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<listitem arch="i386"><para>
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The compact and idepci flavors don't come with sound. Although
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the vanilla kernel does, it might not work for other reasons.
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</para></listitem>
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<listitem><para>
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optimize the kernel by removing useless drivers to speed up boot
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time
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</para></listitem>
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<listitem><para>
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use options of the kernel which are not supported by the default
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kernel (such as network firewalling)
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</para></listitem>
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<listitem><para>
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run a updated or development kernel
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</para></listitem>
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<listitem><para>
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impress your friends, try new things
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</para></listitem>
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</itemizedlist>
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</para>
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<sect2><title>Kernel Image Management</title>
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<para>
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Don't be afraid to try compiling the kernel. It's fun and profitable.
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</para><para>
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To compile a kernel the Debian way, you need some packages:
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<classname>kernel-package</classname>,
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<classname>kernel-source-&kernelversion;</classname> (the most recent version
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at the time of this writing), <classname>fakeroot</classname> and a
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few others which are probably already installed (see
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<filename>/usr/share/doc/kernel-package/README.gz</filename> for the
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complete list).
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</para><para>
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This method will make a .deb of your kernel source, and, if you have
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non-standard modules, make a synchronized dependent .deb of those
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too. It's a better way to manage kernel images;
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<filename>/boot</filename> will hold the kernel, the System.map, and a
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log of the active config file for the build.
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</para><para>
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Note that you don't <emphasis>have</emphasis> to compile your kernel
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the ``Debian way''; but we find that using the packaging system to
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manage your kernel is actually safer and easier. In fact, you can get
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your kernel sources right from Linus instead of
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<classname>kernel-source-&kernelversion;</classname>, yet still use the
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<classname>kernel-package</classname> compilation method.
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</para><para>
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Note that you'll find complete documentation on using
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<classname>kernel-package</classname> under
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<filename>/usr/share/doc/kernel-package</filename>. This section just
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contains a brief tutorial.
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</para><para arch="sparc">
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If you are compiling a kernel for UltraSPARC you will need to be sure
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you have installed the <classname>egcs64</classname> package. This is
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the preferred compiler for 64bit SPARC kernels. The default
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<command>gcc</command> will also compile 64bit kernels, but is not as
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stable. Plus, if you do not use <classname>egcs64</classname> and you
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encounter kernel problems, you will most likely be asked to recompile
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the kernel using <classname>egcs64</classname> in order to verify your
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problem still exists. After installing <classname>egcs64</classname>
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be sure to run <userinput>update-alternatives --config
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sparc64-linux-gcc</userinput> as root, and be sure that
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<classname>egcs64</classname> is being used for this program.
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</para><para>
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Hereafter, we'll assume your kernel source will be located in
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<filename>/usr/local/src</filename> and that your kernel version is
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&kernelversion;. As root, create a directory under
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<filename>/usr/local/src</filename> and change the owner of that
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directory to your normal non-root account. As your normal non-root
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account, change your directory to where you want to unpack the kernel
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sources (<userinput>cd /usr/local/src</userinput>), extract the kernel
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sources (<userinput>tar xIf
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/usr/src/kernel-source-&kernelversion;.tar.bz2</userinput>), change your
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directory to it (<userinput>cd
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kernel-source-&kernelversion;/</userinput>).
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</para><para>
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Now, you can configure your kernel. Run <userinput>make
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xconfig</userinput> if X11 is installed, configured and being run,
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<userinput>make menuconfig</userinput> otherwise (you'll need
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<classname>ncurses-dev</classname> installed). Take the time to read
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the online help and choose carefully. When in doubt, it is typically
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better to include the device driver (the software which manages
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hardware peripherals, such as Ethernet cards, SCSI controllers, and so
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on) you are unsure about. Be careful: other options, not related to a
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specific hardware, should be left at the default value if you do not
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understand them. Do not forget to select ``Kernel module loader'' in
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``Loadable module support''
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<phrase arch="alpha"> and ``Enhanced Real Time
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Clock Support'' in ``Character devices'' (they are </phrase>
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<phrase arch="not-alpha"> (it is </phrase>
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not selected by default). If not included, your Debian installation
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will experience problems.
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</para><para>
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Clean the source tree and reset the <classname>kernel-package</classname>
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parameters. To do that, do <userinput>make-kpkg clean</userinput>.
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</para><para>
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Now, compile the kernel:
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<userinput>fakeroot make-kpkg --revision=custom.1.0 kernel_image</userinput>.
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The version number of ``1.0'' can be changed at will; this is just a
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version number that you will use to track your kernel builds.
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Likewise, you can put any word you like in place of ``custom'' (e.g.,
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a host name). Kernel compilation may take quite a while, depending on
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the power of your machine.
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</para><para condition="supports-pcmcia">
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If you require PCMCIA support, you'll also need to install the
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<classname>pcmcia-source</classname> package. Unpack the gzipped tar file
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as root in the directory <filename>/usr/src</filename> (it's important that
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modules are found where they are expected to be found, namely,
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<filename>/usr/src/modules</filename>). Then, as root, do <userinput>make-kpkg
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modules_image</userinput>.
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</para><para>
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Once the compilation is complete, you can install your custom kernel
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like any package. As root, do <userinput>dpkg -i
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../kernel-image-&kernelversion;-<replaceable>subarchitecture</replaceable>_custom.1.0_&architecture;.deb</userinput>.
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The <replaceable>subarchitecture</replaceable> part is an optional
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sub-architecture,
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<phrase arch="i386"> such as ``i586'', </phrase>
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depending on what kernel options you set.
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<userinput>dpkg -i kernel-image...</userinput> will install the
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kernel, along with some other nice supporting files. For instance,
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the <filename>System.map</filename> will be properly installed
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(helpful for debugging kernel problems), and
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<filename>/boot/config-&kernelversion;</filename> will be installed,
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containing your current configuration set. Your new
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<classname>kernel-image-&kernelversion;</classname> package is also clever
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enough to automatically use your platform's boot-loader to run an
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update on the booting, allowing you to boot without re-running the
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boot loader. If you have created a modules package, e.g., if you have
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PCMCIA, you'll need to install that package as well.
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</para><para>
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It is time to reboot the system: read carefully any warning that the
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above step may have produced, then <userinput>shutdown -r now</userinput>.
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</para><para>
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For more information on <classname>kernel-package</classname>, read
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the fine documentation in <filename>/usr/share/doc/kernel-package</filename>.
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</para>
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</sect2>
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</sect1>
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