Linux Kernel

Documentation

kernel option docs	https://www.kernel.org/doc/html/v4.14/admin-guide/kernel-parameters.html
tut: kernel programming guide	https://sysprog21.github.io/lkmpg/

Locations

/etc/modprobe.d/*.conf	load kernel modules on startup
/lib/modules/$(uname -r)/*	kernel modules (modules.builtin lists builtin modules)

Notes

linux kernel configuration

linux kernel event queue

Kernel Options

Your can add boot options for your kernel.
The location depends on your bootloader, for systemd-boot it would be in a file like /boot/loader/entries/archlinux.conf.

# /boot/loader/entries/archlinux.conf

# ...
options rdblacklist=nouveau nofb nomodeset

Some useful kernel options

nofb       # disable framebuffer
nomodeset  # disable kernel modesetting (increased resolution)

Kernel Modules

/etc/modprobe.d/*.conf

location of kernel-module files

Managing Kernel Modules

lsmod                                          # list loaded kernel modules
modinfo btusb                                  # list kernel options for btusb
modprobe btusb                                 # load 'btusb' kernel module
cat /lib/modules/$(uname -r)/modules.builtin   # list builtin kernel modules

Automatically loading kernel modules

Similar to other systemd files, you can gather a bunch of kernel modules in a single file. The syntax of the file is a newline separated list of modules. Their names will be exactly as they would be called by modprobe. A newline with a first character of '#', marks a comment.

/etc/modprobe.d/wiimote.conf

# /etc/modprobe.d/{yourname}.conf
uinput
btusb

Dynamic Kernel Modules (DKMS)

DKMS packages include kernel modules that are recompiled every time a new kernel is installed.
You can safely install/build these modules after an update without reboot, but you'll need to restart to use them (so the new kernel is used).
Most distros use the -dkms suffix to indicate a package like this.

Kernel Downgrades

Boot your distro off a USB stick, and chroot into your existing installation. You'll need to uninstall all packages that are particular to your kernel version like linux, linux-headers, virtualbox-host-modules, virtualbox-guest-modules.

# Connect to the internet
sudo mount /dev/sda2 /mnt
arch-chroot /mnt /bin/bash
cd /var/cache/pacman/pkg

pacman -Rs linux-3.9.7 linux-headers-3.9.7 virtualbox-host-modules virtualbox-guest-modules
pacman -U linux-3.7.1 linux-headers 3.7.1
exit

sudo reboot