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<title>Selecting a Kernel</title>
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<th colspan="3" align="center">Slackware Linux Essentials</th>
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<tr>
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<td width="10%" align="left" valign="bottom"><a href="system-configuration.html"
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accesskey="P">Prev</a></td>
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<td width="80%" align="center" valign="bottom">Chapter 4 System Configuration</td>
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accesskey="N">Next</a></td>
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</div>
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<div class="SECT1">
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<h1 class="SECT1"><a id="SYSTEM-CONFIGURATION-KERNEL"
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name="SYSTEM-CONFIGURATION-KERNEL">4.2 Selecting a Kernel</a></h1>
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<p>The kernel is the part of the operating system that provides hardware access, process
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control, and overall system control. The kernel contains support for your hardware
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devices, so picking one for your system is an important setup step.</p>
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<p>Slackware provides more than a dozen precompiled kernels that you can pick from, each
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with a standard set of drivers and additional specific drivers. You can run one of the
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precompiled kernels or you can build your own kernel from source. Either way, you need to
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make sure that your kernel has the hardware support your system needs.</p>
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<div class="SECT2">
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<h2 class="SECT2"><a id="AEN1581" name="AEN1581">4.2.1 The <tt
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class="FILENAME">/kernels</tt> Directory on the Slackware CD-ROM</a></h2>
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<p>The precompiled Slackware kernels are available in the <tt
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class="FILENAME">/kernels</tt> directory on the Slackware CD-ROM or on the FTP site in
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the main Slackware directory. The available kernels change as new releases are made, so
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the documentation in that directory is always the authoritative source. The <tt
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class="FILENAME">/kernels</tt> directory has subdirectories for each kernel available.
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The subdirectories have the same name as their accompanying boot disk. In each
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subdirectory you will find the following files:</p>
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<div class="INFORMALTABLE"><a id="AEN1587" name="AEN1587"></a>
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<table border="0" frame="void" width="100%" class="CALSTABLE">
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<col width="33%" />
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<col width="67%" />
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<thead>
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<tr>
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<th>File</th>
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<th>Purpose</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><tt class="FILENAME">System.map</tt></td>
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<td>The system map file for this kernel</td>
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</tr>
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<tr>
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<td><tt class="FILENAME">bzImage</tt></td>
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<td>The actual kernel image</td>
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</tr>
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<tr>
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<td><tt class="FILENAME">config</tt></td>
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<td>The source configuration file for this kernel</td>
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</tr>
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</tbody>
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</table>
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</div>
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<p>To use a kernel, copy the <tt class="FILENAME">System.map</tt> and <tt
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class="FILENAME">config</tt> files to your <tt class="FILENAME">/boot</tt> directory and
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copy the kernel image to <tt class="FILENAME">/boot/vmlinuz</tt>. Run <tt
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class="COMMAND">/sbin/lilo</tt>(8) to install LILO for the new kernel, and then reboot
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your system. That's all there is to installing a new kernel.</p>
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<p>The kernels that end with a .i are IDE kernels. That is, they include no SCSI support
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in the base kernel. The kernels that end with .s are SCSI kernels. They include all the
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IDE support in .i kernels, plus SCSI support.</p>
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</div>
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<div class="SECT2">
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<h2 class="SECT2"><a id="SYSTEM-CONFIGURATION-KERNEL-COMPILE"
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name="SYSTEM-CONFIGURATION-KERNEL-COMPILE">4.2.2 Compiling a Kernel from Source</a></h2>
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<p>The question “Should I compile a kernel for my system?” is often asked by
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new users. The answer is a definite maybe. There are few instances where you will need to
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compile a kernel specific to your system. Most users can use a precompiled kernel and the
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loadable kernel modules to achieve a fully working system. You will want to compile a
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kernel for your system if you are upgrading kernel versions to one that we do not
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currently offer in Slackware, or if you have patched the kernel source to get special
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device support that is not in the native kernel source. Anyone with an SMP system will
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definitely want to compile a kernel with SMP support. Also, many users find a custom
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compiled kernel runs much faster on their machine. You may find it useful to compile the
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kernel with optimizations for the specific processor in your machine.</p>
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<p>Building your own kernel is not that hard. The first step is to make sure you have the
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kernel source installed on your system. Make sure that you installed the packages from
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the K series during the installation. You will also want to make sure you have the D
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series installed, specifically the C compiler, GNU make, and GNU binutils. In general,
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it's a good idea to have the entire D series installed if you plan on doing any kind of
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development. You can also download the latest kernel source from <a
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href="http://www.kernel.org/mirrors" target="_top">http://www.kernel.org/mirrors</a>.</p>
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<div class="SECT3">
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<h3 class="SECT3"><a id="AEN1624" name="AEN1624">4.2.2.1 Linux Kernel version 2.4.x
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Compilation</a></h3>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre class="SCREEN">
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<samp class="PROMPT">%</samp> <kbd class="USERINPUT">su -</kbd>
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Password:
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">cd /usr/src/linux</kbd>
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</pre>
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</td>
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</tr>
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</table>
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<p>The first step is to bring the kernel source into its base state. We issue this
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command to do that (note, you may wish to back-up the <tt class="FILENAME">.config</tt>
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file as this command will delete it without warning):</p>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre class="SCREEN">
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">make mrproper</kbd>
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</pre>
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</td>
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</tr>
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</table>
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<p>Now you can configure the kernel for your system. The current kernel offers three ways
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of doing this. The first is the original text-based question and answer system. It asks a
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bunch of questions and then builds a configuration file. The problem with this method is
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that if you mess up, you must start over. The method that most people prefer is the menu
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driven one. Lastly, there is an X-based kernel configuration tool. Pick the one you want
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and issue the appropriate command:</p>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre class="SCREEN">
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<samp class="PROMPT">#</samp> <kbd
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class="USERINPUT">make config</kbd> (text-based Q&A version)
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<samp class="PROMPT">#</samp> <kbd
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class="USERINPUT">make menuconfig</kbd> (menu driven, text-based version)
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<samp class="PROMPT">#</samp> <kbd
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class="USERINPUT">make xconfig</kbd> (X-based version, make sure you are in X first)
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</pre>
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</td>
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</tr>
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</table>
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<div class="FIGURE"><a id="SYSTEM-CONFIGURATION-MAKE-MENUCONFIG"
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name="SYSTEM-CONFIGURATION-MAKE-MENUCONFIG"></a>
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<p><b>Figure 4-1. Kernel Configuration Menu</b></p>
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<p><img src="system-configuration/make-menuconfig-w.png" /></p>
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</div>
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<p>New users will probably find <tt class="COMMAND">menuconfig</tt> to be the easiest to
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use. Help screens are provided that explain the various parts of the kernel. After
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configuring your kernel, exit the configuration program. It will write the necessary
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configuration files. Now we can prepare the source tree for a build:</p>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre class="SCREEN">
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">make dep</kbd>
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">make clean</kbd>
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</pre>
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</td>
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</tr>
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</table>
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<p>The next step is to compile the kernel. First try issuing the <tt
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class="COMMAND">bzImage</tt> command below.</p>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre class="SCREEN">
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">make bzImage</kbd>
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</pre>
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</td>
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</tr>
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</table>
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<p>This may take a while, depending on your CPU speed. During the build process, you will
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see the compiler messages. After building the kernel image, you will want to build any
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parts of the kernel that you flagged as modular.</p>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre class="SCREEN">
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">make modules</kbd>
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</pre>
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</td>
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</tr>
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</table>
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<p>We can now install the kernel and modules that you compiled. To install the kernel on
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a Slackware system, these commands should be issued:</p>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre class="SCREEN">
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<samp class="PROMPT">#</samp> <kbd
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class="USERINPUT">mv /boot/vmlinuz /boot/vmlinuz.old</kbd>
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<samp class="PROMPT">#</samp> <kbd
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class="USERINPUT">cat arch/i386/boot/bzImage > /vmlinuz</kbd>
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<samp class="PROMPT">#</samp> <kbd
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class="USERINPUT">mv /boot/System.map /boot/System.map.old</kbd>
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">cp System.map /boot/System.map</kbd>
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">make modules_install</kbd>
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</pre>
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</td>
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</tr>
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</table>
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<p>You will want to edit <tt class="FILENAME">/etc/lilo.conf</tt> and add a section to
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boot your old kernel in case your new one does not work. After doing that, run <tt
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class="COMMAND">/sbin/lilo</tt> to install the new boot block. You can now reboot with
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your new kernel.</p>
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</div>
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<div class="SECT3">
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<h3 class="SECT3"><a id="AEN1686" name="AEN1686">4.2.2.2 Linux Kernel Version
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2.6.x</a></h3>
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<p>The compilation of a 2.6 kernel is only slightly different from a 2.4 or a 2.2 kernel,
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but it is important that you understand the differences before delving in. It's no longer
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necessary to run <tt class="COMMAND">make dep</tt> and <tt class="COMMAND">make
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clean</tt>. Also, the kernel compilation process is not as verbose in the 2.6 kernel
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series. This results in a build process that is easier to understand, but has some short
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comings as well. If you have trouble building the kernel, it's highly recommended that
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you turn verbosity back up. You do this simply by appending <var class="OPTION">V=1</var>
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to the build. This allows you to log more information that could help a kernel developer
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or other friendly geek aid you in resolving the issue.</p>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre class="SCREEN">
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">make bzImage V=1</kbd>
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</pre>
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</td>
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</tr>
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</table>
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</div>
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</div>
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<div class="SECT2">
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<h2 class="SECT2"><a id="SYSTEM-CONFIGURATION-KERNEL-MODULES"
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name="SYSTEM-CONFIGURATION-KERNEL-MODULES">4.2.3 Using Kernel Modules</a></h2>
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<p>Kernel modules are another name for device drivers that can be inserted into a running
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kernel. They allow you to extend the hardware supported by your kernel without needing to
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pick another kernel or compile one yourself.</p>
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<p>Modules can also be loaded and unloaded at any time, even when the system is running.
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This makes upgrading specific drivers easy for system administrators. A new module can be
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compiled, the old one removed, and the new one loaded, all without rebooting the
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machine.</p>
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<p>Modules are stored in the <tt class="FILENAME">/lib/modules/<var
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class="REPLACEABLE">kernel version</var></tt> directory on your system. They can be
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loaded at boot time through the <tt class="FILENAME">rc.modules</tt> file. This file is
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very well commented and offers examples for major hardware components. To see a list of
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modules that are currently active, use the <tt class="COMMAND">lsmod</tt>(1) command:</p>
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<table border="0" bgcolor="#E0E0E0" width="100%">
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<tr>
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<td>
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<pre class="SCREEN">
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<samp class="PROMPT">#</samp> <kbd class="USERINPUT">lsmod</kbd>
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Module Size Used by
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parport_pc 7220 0
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parport 7844 0 [parport_pc]
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</pre>
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</td>
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</tr>
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</table>
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<p>You can see here that I only have the parallel port module loaded. To remove a module,
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you use the <tt class="COMMAND">rmmod</tt>(1) command. Modules can be loaded by the <tt
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class="COMMAND">modprobe</tt>(1) or <tt class="COMMAND">insmod</tt>(1) command. <tt
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class="COMMAND">modprobe</tt> is usually safer because it will load any modules that the
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one you're trying to load depends on.</p>
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<p>A lot of users never have to load or unload modules by hand. They use the kernel
|
||
|
|
autoloader for module management. By default, Slackware includes <var
|
||
|
|
class="OPTION">kmod</var> in its kernels. <var class="OPTION">kmod</var> is a kernel
|
||
|
|
option that enables the kernel to automatically load modules as they are requested. For
|
||
|
|
more information on <var class="OPTION">kmod</var> and how it is configured, see <tt
|
||
|
|
class="FILENAME">/usr/src/linux/Documentation/kmod.txt</tt>. You'll have needed to have
|
||
|
|
the kernel source package, or downloaded kernel source from <a href="http://kernel.org"
|
||
|
|
target="_top">http://kernel.org</a>.</p>
|
||
|
|
|
||
|
|
<p>More information can be found in the man pages for each of these commands, plus the
|
||
|
|
<tt class="FILENAME">rc.modules</tt> file.</p>
|
||
|
|
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|
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