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Why I wrote Install Kernel (ik) and How It Works

By Justin Piszcz

ik (Install Kernel) is available at and

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. 

Copyright © 2002, Justin Piszcz.
Copying license
Published in Issue 75 of Linux Gazette, February 2002

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