8.3. Linux-

The Linux package contains the Linux kernel.

Approximate build time: 4.20 SBU
Required disk space: 181 MB
Installation depends on: Bash, Binutils, Coreutils, Findutils, GCC, Glibc, Grep, Gzip, Make, Modutils, Perl, and Sed

8.3.1. Installation of the kernel

Building the kernel involves a few steps—configuration, compilation, and installation. Read the README file in the kernel source tree for alternative methods to the way this book configures the kernel.

Prepare for compilation by running the following command:

make mrproper

This ensures that the kernel tree is absolutely clean. The kernel team recommends that this command be issued prior to each kernel compilation. Do not rely on the source tree being clean after un-tarring.

If, in Section 7.6, “Configuring the Linux Console,” it was decided to compile the keymap into the kernel, issue the command below:

loadkeys -m /usr/share/kbd/keymaps/[path to  keymap] > \

For example, if using a Dutch keyboard, use /usr/share/kbd/keymaps/i386/qwerty/nl.map.gz.

Configure the kernel via a menu-driven interface. BLFS has some information regarding particular kernel configuration requirements of packages outside of LFS at http://www.linuxfromscratch.org/blfs/view/svn/longindex.html#kernel-config-index:

make menuconfig

Alternatively, make oldconfig may be more appropriate in some situations. See the README file for more information.

If desired, skip kernel configuration by copying the kernel config file, .config, from the host system (assuming it is available) to the unpacked linux- directory. However, we do not recommend this option. It is often better to explore all the configuration menus and create the kernel configuration from scratch.



NPTL requires the kernel to be compiled with GCC-3.x, in this case 3.4.3. It is not recommended to compile the kernel with GCC-2.95.x, as this causes failures in the Glibc test suite. Normally, this wouldn't be mentioned as LFS doesn't build GCC-2.95.x. Unfortunately, the kernel documentation is outdated and still claims GCC-2.95.3 is the recommended compiler.

Compile the kernel image and modules:


If using kernel modules, an /etc/modprobe.conf file may be needed. Information pertaining to modules and kernel configuration is located in the kernel documentation in the linux- directory. Also, modprobe.conf(5) may be of interest.

Be very careful when reading other documentation relating to kernel modules because it usually applies to 2.4.x kernels only. As far as we know, kernel configuration issues specific to Hotplug and Udev are not documented. The problem is that Udev will create a device node only if Hotplug or a user-written script inserts the corresponding module into the kernel, and not all modules are detectable by Hotplug. Note that statements like the one below in the /etc/modprobe.conf file do not work with Udev:

alias char-major-XXX some-module

Because of the complications with Hotplug, Udev, and modules, we strongly recommend starting with a completely non-modular kernel configuration, especially if this is the first time using Udev.

Install the modules, if the kernel configuration uses them:

make modules_install

After kernel compilation is complete, additional steps are required to complete the installation. Some files need to be copied to the /boot directory.

The path to the kernel image may vary depending on the platform being used. The following command assumes an x86 architecture:

cp arch/i386/boot/bzImage /boot/lfskernel-

System.map is a symbol file for the kernel. It maps the function entry points of every function in the kernel API, as well as the addresses of the kernel data structures for the running kernel. Issue the following command to install the map file:

cp System.map /boot/System.map-

The kernel configuration file .config produced by the make menuconfig step above contains all the configuration selections for the kernel that was just compiled. It is a good idea to keep this file for future reference:

cp .config /boot/config-

It is important to note that the files in the kernel source directory are not owned by root. Whenever a package is unpacked as user root (like we did inside chroot), the files have the user and group IDs of whatever they were on the packager's computer. This is usually not a problem for any other package to be installed because the source tree is removed after the installation. However, the Linux source tree is often retained for a long time. Because of this, there is a chance that whatever user ID the packager used will be assigned to somebody on the machine. That person would then have write access to the kernel source.

If the kernel source tree is going to be retained, run chown -R 0:0 on the linux- directory to ensure all files are owned by user root.



Some kernel documentation recommends creating a symlink from /usr/src/linux pointing to the kernel source directory. This is specific to kernels prior to the 2.6 series and must not be created on an LFS system as it can cause problems for packages you may wish to build once your base LFS system is complete.

Also, the headers in the system's include directory should always be the ones against which Glibc was compiled, that is, the ones from the Linux-Libc-Headers package, and therefore, should never be replaced by the kernel headers.

8.3.2. Contents of Linux

Installed files: config-, lfskernel-, and System.map-

Short Descriptions


Contains all the configuration selections for the kernel


The engine of the Linux system. When turning on the computer, the kernel is the first part of the operating system that gets loaded. It detects and initializes all components of the computer's hardware, then makes these components available as a tree of files to the software and turns a single CPU into a multitasking machine capable of running scores of programs seemingly at the same time


A list of addresses and symbols; it maps the entry points and addresses of all the functions and data structures in the kernel