From:	 Justin Piszcz <war@starband.net>
To:	 Jonathan Corbet <corbet@lwn.net>, Linux Gazette <gazette@ssc.com>
Subject: Install Kernel (HTML) + (TXT) + (FIXED) VER
Date:	 Tue, 29 Jan 2002 09:39:56 -0500

ik (Install Kernel) is available at http://www.ramdown.com/war/ik.

In December 2000, after four years of using Linux, compiling and installing
kernels became a waste of my time. I chose to write my own kernel
installation and setup script called Install Kernel, because no other
scripts existed at the time, and I needed something that would install the
Linux kernel and automatically setup my bootloader configuration file with
no user intervention. Install Kernel interfaces with the Linux operating
system by moving and editing files. When not using ik, the majority of time
consumed when updating a kernel mainly consists of moving files around and
setting up configuration files. The ik script has three basic parts:
dependency checks, compiling the kernel and moving the files to their
proper locations, and editing boot loader configuration files. Install
Kernel aims to help people who are either new to installing the kernel or
people who choose to use their time efficiently.

Every operating system has some type of kernel; the kernel is the core of
the operating system. The current kernel version as of this writing is
Linux 2.4.17. Most users either recompile or upgrade their kernels. One may
choose to upgrade his or her kernel in order to add support for a certain
device attached to his or her computer. For instance, if one bought a
Universal Serial Bus (USB) scanner, he or she would have to make the
appropriate changes to the kernel configuration file, and recompile and
install the new kernel. Reasons for upgrading the kernel may include a
better virtual memory subsystem, or important security fixes. An example
would be Linux kernel version 2.4.11.  This kernel was vulnerable to a
symlink denial of service attack, prompting users running 2.4.11 to
immediately upgrade to 2.4.12 when it became available due to this
vulnerability. These are the fundamental reasons of why one may want to
either recompile or upgrade his or her kernel.

Install Kernel interfaces with the Linux operating system by running a
series of functions or groups of commands that automate the compiling or
recompiling and installation process. It consists of three groups of
functions: checking dependencies, building the kernel and moving files, and
editing the boot loader configuration file. Grouping all of the functions
in these three groups makes maintaining and altering the script much
easier. Install Kernel can also be considered a program, because a program
does checking and makes choices accordingly. A script is usually a file,
which contains a certain number of commands with no logic in
mind. Therefore, while ik is technically a script, it can also be called a
program.

Dependency checks are to make sure the current system configuration and
settings are properly setup before proceeding with the kernel build. There
are seven dependency checks, they are: a root check, space check, link
check, boot check, boot loader check, configuration check, and a module
check. First, the root check makes sure the user is a super user; which
means they are capable of editing important system files only accessible to
the root account. The space check makes sure there is at least 200
megabytes available. The kernel source these days is around 150 megabytes
just for the source code. When one compiles the kernel, it may increase the
size to 50 megabytes or more.  Therefore, ik checks for at least 200MB
available in order to successfully compile the kernel without running out
of space. Next, it is not required, but it is standard to have a symbolic
link of /usr/src/linux pointing to /usr/src/linux-x.y.z. The fourth check
makes sure the user has a /boot directory, this is where the Linux kernel
files will be installed to. The fifth check determines the bootloader that
will be used. There are two main boot loaders in Linux. LILO and GRUB are
the two most popular for booting the operating system. This check
accurately finds whether the kernel was booted from either LILO or GRUB by
checking which bootloader was used last. It then tells the rest of the
script to edit the correct one accordingly. The sixth configuration check
is to make sure users have created a proper kernel configuration file,
which is used in the process of building the Linux kernel. The final check
is a module check, if modules are turned off, the script will determine
this and alter the installation process to install with no module
support. The main idea behind the depdency checks is to make sure the user
cannot damage his or her system if they do not do something right.

The installation process also contains seven functions. The installation
process is usually several commands. However, because of the differences
that can occur in a user's configuration file, each part of the building
process must be checked and the building process may need to be
altered. The first function makes sure the dependencies are setup correctly
for all files in the kernel source tree. The second function deletes stale
object files and or old kernel files. Next, the third function is the
kernel build function; this function runs a command to build the Linux
kernel. Next, functions four and five make and install modules if the user
had specified module support in his or her kernel configuration file. The
sixth function moves the Linux kernel and its System dependency map to the
boot partition. The last function of the build process sets up module
dependencies for the new kernel if modules were defined. The installation
process also includes a small error check for each part of the kernel build
process. If any part of the kernel build process fails; the script will
abort, not modifying any boot loader configuration files. This is
important; because if it did not abort, it may alter the boot loader
configuration files, thus rendering the system unbootable. It is important
to support every Linux configuration possible because of the wide use of
this script.

The boot loader configuration and setup process is probably the most
important aspect of installing a new kernel. An improper boot loader
configuration may leave one with system that does not boot; or simply does
not boot the new kernel.  It is also important, as some systems may have
two or more boot loaders installed. There are four functions defined for
this process. The first function uses the boot loader, which was defined
during the configuration checks. The second function defines where the LILO
or GRUB configuration files are located.  Next, depending on which boot
loader is found, either LILO or GRUB configuration files are edited
automatically by sed. Sed is a stream editor, which edits a file with no
user intervention. If user intervention were required, the user would have
to be present between certain parts of the kernel installation. With ik, it
makes efficient use of a user's time because only one command needs to be
entered to complete the entire installation and setup process.

Install Kernel is a useful tool for those who are new to Linux, rebuild
their kernel often, or value their time. It reduces the commands for
installing the kernel from about thirteen to one. Users new to Linux may
find this attractive. This is because the entire process is automated; and
if something is not correct, in most cases ik will notify the user what is
incorrect, and how to fix the error. On the other side, for experienced
users who do not wish to spend valuable time installing a new kernel, this
is also very handy. Install Kernel is efficient by requiring no user
intervention and reducing time spent on kernel installs, and effective by
giving new to Linux the option for an easy kernel upgrade.