10.3. Linux-5.10.17

10.3.1. 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.

There are several ways to configure the kernel options. Usually, This is done through a menu-driven interface, for example:

make menuconfig

For general information on kernel configuration see http://www.linuxfromscratch.org/hints/downloads/files/kernel-configuration.txt. BLFS has some information regarding particular kernel configuration requirements of packages outside of LFS at http://www.linuxfromscratch.org/blfs/view/10.1/longindex.html#kernel-config-index. Additional information about configuring and building the kernel can be found at http://www.kroah.com/lkn/

There are several other options that may be desired depending on the requirements for the system. For a list of options needed for BLFS packages, see the BLFS Index of Kernel Settings (http://www.linuxfromscratch.org/blfs/view/10.1/longindex.html#kernel-config-index).

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-5.10.17 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.

Compile the kernel image and modules:

make

If using kernel modules, module configuration in /etc/modprobe.d may be required. Information pertaining to modules and kernel configuration is located in Section 9.3, “Overview of Device and Module Handling” and in the kernel documentation in the linux-5.10.17/Documentation directory. Also, modprobe.d(5) may be of interest.

Unless module support has been disabled in the kernel configuration, install the modules with:

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 filename below can be changed to suit your taste, but the stem of the filename should be vmlinuz to be compatible with the automatic setup of the boot process described in the next section. The following command assumes a MIPS architecture:

cp -iv vmlinuz /boot/vmlinuz-5.10.17-lfs-10.1-mips64el

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. It is used as a resource when investigating kernel problems. Issue the following command to install the map file:

cp -iv System.map /boot/System.map-5.10.17

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 -iv .config /boot/config-5.10.17

Install the documentation for the Linux kernel:

install -d /usr/share/doc/linux-5.10.17
cp -r Documentation/* /usr/share/doc/linux-5.10.17

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.

install -v -m755 -d /etc/modprobe.d
cat > /etc/modprobe.d/usb.conf << "EOF"
# Begin /etc/modprobe.d/usb.conf

install ohci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i ohci_hcd ; true
install uhci_hcd /sbin/modprobe ehci_hcd ; /sbin/modprobe -i uhci_hcd ; true

# End /etc/modprobe.d/usb.conf
EOF