ch01.xml

<chapter id="LKN-introduction">

<title>Introduction</title>

<para>
Despite its large code base (over 7 million lines of code), the Linux
kernel is the most flexible operating system that has ever been created.
It can be tuned for a wide range of different systems, running on
everything from a radio-controlled model helicoptor, to a cellphone, to the
majority of the largest supercomputers in the world.  By customizing the
kernel for your specific environment, it is possible to create something
that is both smaller and faster than the kernel provided by most Linux
distributions.  This book will go into how to build and install a custom
kernel, and provide some hints on how to enable specific options that you
will probably wish to use for different situations.
</para>

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<para>
No Linux distribution provides the exact kernel most of its users want.
Modern distributions have gotten very accommodating, compiling in support
for every known device, for sound, and even for power conservation.  But
you will likely have a need that's different from the majority of users
(and every distribution has to try to meet the needs of the majority). You
may just have different hardware. And when a new kernel comes out, you may
want to start using it without waiting for a distribution to be built
around it.
</para>

<para>
For a host of reasons, you will want during your Linux career to sometimes
build a kernel, or to tweak the parameters of one you are running. This
book gives you the information you need to understand the kernel from a
user's point of view, and to make the most common changes.
</para>

<para>
There are also good reasons to take features out of the kernel,
particularly if you are running it on an embedded system or one with a
small form factor.
</para>

<para>
When tweaking, it's helpful to understand the internals of kernel behavior.
These are beyond the scope of this book, except for brief summaries that
appear with certain options. The bibliography includes references to other
books and material that can give you more background.
</para>

<sect1>
<title>Using this book</title>

<warning>
<para>
Do not configure or build your kernel with superuser permissions enabled!
</para>
</warning>

<para>
The previous warning is the most important thing to remember while working through the steps in
this book.
Everything in this book, from downloading the kernel source code,
uncompressing it, configuring the kernel, and building it should be done as
a normal user on the machine.  Only the two or three commands it takes to
install a new kernel should be done as the superuser (<emphasis>root</emphasis>).
</para>

<para>
There have been bugs in the kernel build process in the past, causing some
special files in the <filename>/dev</filename> directory to be deleted if
the user had superuser permissions while building the Linux kernel.
<footnote>
<para>
This took quite a while to fix, as none of the primary kernel
developers build kernels as root, so they did not suffer from the bug.
A number of weeks went by before it was finally determined that the act of
building the kernel was the problem.
A number of kernel developers half-jokingly suggested that the bug remain
in, to help prevent anyone from building the kernel as root, but calmer
heads prevailed and the bug in the build system was fixed.
</para>
</footnote>
There are also issues that can easily arise when uncompressing the Linux
kernel with superuser rights, as some of the files in the kernel
source package will not end up with the proper permissions and will cause build
errors later.
</para>

<para>
The kernel source code should also never be placed in the
<filename>/usr/src/linux/</filename> directory, as that is the location of
the kernel that the system libraries were built against, not your new
custom kernel.  Do not do any kernel development under the
<filename>/usr/src/</filename> directory tree at all, but only in a local
user directory where nothing bad can happen to the system.
</para>


</sect1>


</chapter>

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