13.2. Linux-3.14.21

The Linux package contains the Linux kernel.

13.2.1. 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.

Apply the latest Linux sublevel patch:

xzcat ../patch-3.14.21.xz | patch -Np1 -i -

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.



A good starting place for setting up the kernel configuration is to run make defconfig. This will set the base configuration to a good state that takes your current system architecture into account.

Be sure to configure the following options as shown, or the system might not work correctly or boot at all:

Device Drivers  --->
  Generic Driver Options  --->
    ()  path to uevent helper (CONFIG_UEVENT_HELPER_PATH)
    [*] Maintain a devtmpfs filesystem to mount at /dev (CONFIG_DEVTMPFS)
    [ ] Fallback user-helper invocation for firmware loading (CONFIG_FW_LOADER_USER_HELPER)


"EFI Variable support" and "EFI GUID Partition support" are for UEFI systems.

Configure the kernel via a menu-driven interface. CBLFS has some information regarding particular kernel configuration requirements of packages outside of CLFS at http://cblfs.cross-lfs.org/:

make menuconfig

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

Compile the kernel image and modules:


If using kernel modules, a configuration file in /etc/modprobe.d file may be needed. Information pertaining to modules and kernel configuration is located in the kernel documentation in the Documentation directory of the kernel sources tree. Also, modprobe.d(5) may be of interest.

Install the modules, if the kernel configuration uses them:

make modules_install

Install the firmware, if the kernel configuration uses them:

make firmware_install

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

Issue the following command to install the kernel:

cp -v vmlinux /boot/vmlinux-3.14.21
gzip -9 /boot/vmlinux-3.14.21

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 -v System.map /boot/System.map-3.14.21

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 -v .config /boot/config-3.14.21

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 do inside the final-system build environment), 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 retained, run chown -R 0:0 on the linux-3.14 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 a CLFS system as it can cause problems for packages you may wish to build once your base CLFS system is complete.

Also, the headers in the system's include directory should always be the ones against which Glibc was compiled and should never be replaced by headers from a different kernel version.

13.2.2. Contents of Linux

Installed files: config-[linux-version], clfskernel-[linux-version], and System.map-[linux-version]
Installed directory: /lib/modules

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