Slackware Linux Essentials
Prev	Chapter 4 System Configuration	Next

4.2 Selecting a Kernel

+ +

The kernel is the part of the operating system that provides hardware access, process +control, and overall system control. The kernel contains support for your hardware +devices, so picking one for your system is an important setup step.

+ +

Slackware provides more than a dozen precompiled kernels that you can pick from, each +with a standard set of drivers and additional specific drivers. You can run one of the +precompiled kernels or you can build your own kernel from source. Either way, you need to +make sure that your kernel has the hardware support your system needs.

+ +

4.2.1 The `/kernels` Directory on the Slackware CD-ROM

+ +

The precompiled Slackware kernels are available in the /kernels directory on the Slackware CD-ROM or on the FTP site in +the main Slackware directory. The available kernels change as new releases are made, so +the documentation in that directory is always the authoritative source. The /kernels directory has subdirectories for each kernel available. +The subdirectories have the same name as their accompanying boot disk. In each +subdirectory you will find the following files:

+ +

+ +++ + + + + + + + + + + + + + + + + + + + + + + +

File	Purpose
`System.map`	The system map file for this kernel
`bzImage`	The actual kernel image
`config`	The source configuration file for this kernel

+ +

To use a kernel, copy the System.map and config files to your /boot directory and +copy the kernel image to /boot/vmlinuz. Run /sbin/lilo(8) to install LILO for the new kernel, and then reboot +your system. That's all there is to installing a new kernel.

+ +

The kernels that end with a .i are IDE kernels. That is, they include no SCSI support +in the base kernel. The kernels that end with .s are SCSI kernels. They include all the +IDE support in .i kernels, plus SCSI support.

+ +

4.2.2 Compiling a Kernel from Source

+ +

The question “Should I compile a kernel for my system?” is often asked by +new users. The answer is a definite maybe. There are few instances where you will need to +compile a kernel specific to your system. Most users can use a precompiled kernel and the +loadable kernel modules to achieve a fully working system. You will want to compile a +kernel for your system if you are upgrading kernel versions to one that we do not +currently offer in Slackware, or if you have patched the kernel source to get special +device support that is not in the native kernel source. Anyone with an SMP system will +definitely want to compile a kernel with SMP support. Also, many users find a custom +compiled kernel runs much faster on their machine. You may find it useful to compile the +kernel with optimizations for the specific processor in your machine.

+ +

Building your own kernel is not that hard. The first step is to make sure you have the +kernel source installed on your system. Make sure that you installed the packages from +the K series during the installation. You will also want to make sure you have the D +series installed, specifically the C compiler, GNU make, and GNU binutils. In general, +it's a good idea to have the entire D series installed if you plan on doing any kind of +development. You can also download the latest kernel source from http://www.kernel.org/mirrors.

+ +

4.2.2.1 Linux Kernel version 2.4.x +Compilation

+ + + + + +

+% su -
+Password:
+# cd /usr/src/linux
+

+ +

The first step is to bring the kernel source into its base state. We issue this +command to do that (note, you may wish to back-up the .config +file as this command will delete it without warning):

+ + + + + +

+# make mrproper
+

+ +

Now you can configure the kernel for your system. The current kernel offers three ways +of doing this. The first is the original text-based question and answer system. It asks a +bunch of questions and then builds a configuration file. The problem with this method is +that if you mess up, you must start over. The method that most people prefer is the menu +driven one. Lastly, there is an X-based kernel configuration tool. Pick the one you want +and issue the appropriate command:

+ + + + + +

+# make config           (text-based Q&A version)
+# make menuconfig       (menu driven, text-based version)
+# make xconfig          (X-based version, make sure you are in X first)
+

+ +

Figure 4-1. Kernel Configuration Menu

+ +

New users will probably find menuconfig to be the easiest to +use. Help screens are provided that explain the various parts of the kernel. After +configuring your kernel, exit the configuration program. It will write the necessary +configuration files. Now we can prepare the source tree for a build:

+ + + + + +

+# make dep
+# make clean
+

+ +

The next step is to compile the kernel. First try issuing the bzImage command below.

+ + + + + +

+# make bzImage
+

+ +

This may take a while, depending on your CPU speed. During the build process, you will +see the compiler messages. After building the kernel image, you will want to build any +parts of the kernel that you flagged as modular.

+ + + + + +

+# make modules
+

+ +

We can now install the kernel and modules that you compiled. To install the kernel on +a Slackware system, these commands should be issued:

+ + + + + +

+# mv /boot/vmlinuz /boot/vmlinuz.old
+# cat arch/i386/boot/bzImage > /vmlinuz
+# mv /boot/System.map /boot/System.map.old
+# cp System.map /boot/System.map
+# make modules_install
+

+ +

You will want to edit /etc/lilo.conf and add a section to +boot your old kernel in case your new one does not work. After doing that, run /sbin/lilo to install the new boot block. You can now reboot with +your new kernel.

+ +

4.2.2.2 Linux Kernel Version +2.6.x

+ +

The compilation of a 2.6 kernel is only slightly different from a 2.4 or a 2.2 kernel, +but it is important that you understand the differences before delving in. It's no longer +necessary to run make dep and make +clean. Also, the kernel compilation process is not as verbose in the 2.6 kernel +series. This results in a build process that is easier to understand, but has some short +comings as well. If you have trouble building the kernel, it's highly recommended that +you turn verbosity back up. You do this simply by appending V=1 +to the build. This allows you to log more information that could help a kernel developer +or other friendly geek aid you in resolving the issue.

+ + + + + +

+# make bzImage V=1
+

+ +

4.2.3 Using Kernel Modules

+ +

Kernel modules are another name for device drivers that can be inserted into a running +kernel. They allow you to extend the hardware supported by your kernel without needing to +pick another kernel or compile one yourself.

+ +

Modules can also be loaded and unloaded at any time, even when the system is running. +This makes upgrading specific drivers easy for system administrators. A new module can be +compiled, the old one removed, and the new one loaded, all without rebooting the +machine.

+ +

Modules are stored in the /lib/modules/kernel version directory on your system. They can be +loaded at boot time through the rc.modules file. This file is +very well commented and offers examples for major hardware components. To see a list of +modules that are currently active, use the lsmod(1) command:

+ + + + + +

+# lsmod
+Module                  Size  Used by
+parport_pc              7220   0 
+parport                 7844   0  [parport_pc]
+

+ +

You can see here that I only have the parallel port module loaded. To remove a module, +you use the rmmod(1) command. Modules can be loaded by the modprobe(1) or insmod(1) command. modprobe is usually safer because it will load any modules that the +one you're trying to load depends on.

+ +

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 kmod in its kernels. kmod is a kernel +option that enables the kernel to automatically load modules as they are requested. For +more information on kmod and how it is configured, see /usr/src/linux/Documentation/kmod.txt. You'll have needed to have +the kernel source package, or downloaded kernel source from http://kernel.org.

+ +

More information can be found in the man pages for each of these commands, plus the +rc.modules file.

4.2 Selecting a Kernel

4.2.1 The /kernels Directory on the Slackware CD-ROM

4.2.2 Compiling a Kernel from Source

4.2.2.1 Linux Kernel version 2.4.x +Compilation

4.2.2.2 Linux Kernel Version +2.6.x

4.2.3 Using Kernel Modules

4.2.1 The `/kernels` Directory on the Slackware CD-ROM