Kernel

lz4 is faster to compress than gzip
lz4 is blazingly fast to decompress
lzma is dog slow to compress and decompress, but is tiny
lz4 size weight over gzip is marginal (14%) but imho worth the improved boot time & initrd creation time
xz is potentially even slower and even smaller than lzma
zstd compress at speeds approaching lz4, decompressions at speeds more than twice as fast as zlib, and quality approaching lzma

Device Drivers

Writing a Linux Kernel Module — Part 1: Introduction | derekmolloy.ie
Writing a Linux Kernel Module — Part 2: A Character Device | derekmolloy.ie
Writing a Linux Loadable Kernel Module (LKM) - Interfacing to GPIOs | derekmolloy.ie
Writing a Linux Loadable Kernel Module (LKM) - Interfacing to GPIOs | derekmolloy.ie
exploringBB/extras/kernel at master · derekmolloy/exploringBB

Understanding the Structure of a Linux Kernel Device Driver - Sergio Prado, Toradex - YouTube

Kernel modules

/etc/modules-load.d/
/usr/lib/modules-load.d/

systemctl status systemd-modules-load.service

DKMS

Dynamic Kernel Module Support - Wikiwand
Dynamic Kernel Module Support - ArchWiki
Kernel Korner - Exploring Dynamic Kernel Module Support (DKMS) | Linux Journal

Recompiles drivers against kernel header on host on every driver update OR kernel update.

Device Tree

Index of /doc/Documentation/devicetree/
Device tree - Wikiwand

Device Tree Tutorial (ARM) – Linux Kernel For Newbies
Device Tree Reference - eLinux.org
Device Tree for Dummies (PDF)

A Tutorial on the Device Tree (Zynq) -- Part I | xillybus.com
A Tutorial on the Device Tree (Zynq) -- Part II | xillybus.com
A Tutorial on the Device Tree (Zynq) -- Part III | xillybus.com
A Tutorial on the Device Tree (Zynq) -- Part IV | xillybus.com
A Tutorial on the Device Tree (Zynq) -- Part V | xillybus.com

USB subsystem

Ubuntu Buzz !: Reset USB 2.0 (ehci) & USB 3.0 (xhci) Without Reboot in Linux Kernel
Linux USB FAQ

Audio subsystem

Linux Audio Explained (ALSA vs PulseAudio vs JACK vs Pipewire Explained) - YouTube

sysctl

sysctl - read/write system parameters - System Calls
Sysctl Explorer

GPIO/sysfs

One way of accessing GPIO is to modify the device tree and write a device driver for it.
We could also expose the GPIO via Sysfs interface ("pinctrl" driver) (/sys/class/gpio) to allow access on user space.

GPIO - eLinux.org
Access GPIO from Linux user space
Working with GPIO on the Wandboard and Writing an Android Driver for GPIO Interrupts – Using Android in Industrial Automation with poll()
关于 /sys/class/gpio 简介 - cjsycyl 的专栏 - CSDN 博客
 GPIO 接口解析-wangbaolin719-ChinaUnix 博客
 Controlling GPIO from Linux User Space
RK3399 用户空间 IO 控制 - zhuyong006 的博客 - CSDN 博客

Index of /doc/Documentation/gpio/
https://www.kernel.org/doc/Documentation/gpio/sysfs.txt Sysfs GPIO interface is deprecated
https://www.kernel.org/doc/Documentation/gpio/gpio-legacy.txt
https://www.kernel.org/doc/Documentation/ABI/obsolete/sysfs-gpio
linux/tools/gpio at master · torvalds/linux new interface

vitiral/gpio: python gpio module for linux using the sysfs file access (/sys/class/gpio). Mimics similar Raspberry Pi IO libraries

# get GPIO number in kernel
# 1. refer to spec
# 2. check debug info
cat /sys/kernel/debug/gpio

# export a GPIO pin to userspace
echo $GPIO_NUMBER > /sys/class/gpio/export

echo $GPIO_DIRECTION > /sys/class/gpio/gpio$GPIO_NUMBER/direction  # "in" or "out"
# read and write to pin
cat /sys/class/gpio/gpio$GPIO_NUMBER/value
echo 1 > /sys/class/gpio/gpio$GPIO_NUMBER/value

# clean up
echo $GPIO_NUMBER > /sys/class/gpio/unexport

# debug
mount -t debugfs debugfs /sys/kernel/debug
cat /sys/kernel/debug/gpio

I2C

Index of /doc/Documentation/i2c/
https://www.kernel.org/doc/Documentation/i2c/smbus-protocol
On Linux with proper driver installed, it is exposed as /dev/i2c-N

bjornt/pysmbus
kplindegaard/smbus2: A drop-in replacement for smbus-cffi/smbus-python in pure Python

SPI

Index of /doc/Documentation/spi/
https://www.kernel.org/doc/Documentation/spi/spi-summary

On Linux with proper driver installed, it is exposed as /dev/spidevX.Y

Video Driver

Proprietary (non-free) drivers is a source of problem. You will have to rebuild the driver every time the kernel is updated. Otherwise X will fail to start.
If performance is not an issue it is recommended to use the free drivers.

Bumblebee - ArchWiki

Hybrid graphics

Hybrid graphics - ArchWiki
Bumblebee - ArchWiki
NVIDIA Optimus - ArchWiki

Optimus Technology|NVIDIA
HybridGraphics - Community Help Wiki
How To Switch Between Intel and Nvidia Graphics Card on Ubuntu

The State of NVIDIA Optimus on Linux | The Linux Rain

wildtruc/nvidia-prime-select: This a fork of FedoraPrime enhanced for all linux distributions

File Locks

flock - apply or remove an advisory lock on an open file ("BSD Locks")
fcntl - manipulate file descriptor - System Calls | ManKier ("POSIX Locks")

lockf - apply, test or remove a POSIX lock on an open file
lsof - list open files - man page | ManKier

Checking locked files:

sudo lsof -n <file>
sudo lsof +f -- /dev/mapper/cachedev1

udev

udev - ArchWiki
Writing udev rules
Scripting with udev - jasonwryan.com

procfs

/proc Talk » Linux Magazine
Troubleshoot using the proc filesystem on Linux | Opensource.com

RPi

Department of Computer Science and Technology – Raspberry Pi: Baking Pi – Operating Systems Development
Tutorial | Building an Operating System for the Raspberry Pi
dwelch67/raspberrypi: Raspberry Pi ARM based bare metal examples

Embedded System

Mastering Embedded Linux • &> /dev/null

Unikernel

Unikernel - Wikiwand

oscarlab/graphene: Graphene / Graphene-SGX Library OS - a library OS for Linux multi-process applications, with Intel SGX support
Mini-OS-DevNotes - Xen

Unikernels [Book]

Joyent | Unikernels are unfit for production

Unikernel Linux

Unikernel Linux - Red Hat Research
Unikernel Linux - YouTube

Experimental Patches Adapt Linux For A Unikernel Design - Phoronix
Turning Linux Into A Library Operating System??? - YouTube

Unikernel

Unikernels - Rethinking Cloud Infrastructure (bought by Docker)
Projects | Unikernels Kernel as a lib

Unikernel Systems Joins Docker | Docker Blog
Docker’s Unikernel Experiment Begins Paying Off with Mac OS Libraries - The New Stack
Improving Docker with Unikernels: Introducing HyperKit, VPNKit and DataKit | Docker Blog
docker/hyperkit: A toolkit for embedding hypervisor capabilities in your application

IncludeOS

Unikernels with Idit Levine | Software Engineering Daily Mirage, Rump, UniK

MirageOS

MirageOS build unikernel for network applications, deploy minimum app, written in OCaml
Episode 204: Anil Madhavapeddy on the Mirage Cloud Operating System and the OCaml Language : Software Engineering Radio
My Other Internet is a Mirage

Boots domain 0 OS

Qubes OS

Qubes OS: A reasonably secure operating system | Qubes OS

Rump

POSIX compatible unikernel
Rump Kernels
rumpkernel/rumprun: The Rumprun unikernel and toolchain for various platforms

UniK

unikernels and unik with Scott Weiss | Software Engineering Daily

emc-advanced-dev/unik: The Unikernel Compilation and Deployment Platform Kubernetes for unikernel, supports different providers

Unikernel power comes to Java, Node.js, Go, and Python apps | InfoWorld

Light kernel

see mobile-os.md#google-fuchsia

littlekernel/lk: LK embedded kernel

Microkernel

Microkernel - Wikiwand
Is Linux kernel design outdated? : linux

Kernel

Operating Systems

Linux Kernel

Memory/Virtual Memory

Books

System Calls

Scheduler

Compression

Device Drivers

Kernel modules

DKMS

Device Tree

USB subsystem

Audio subsystem

sysctl

GPIO/sysfs

I2C

SPI

Video Driver

Hybrid graphics

File Locks

udev

procfs

RPi

Embedded System

Unikernel

Unikernel Linux

Unikernel

MirageOS

Qubes OS

Rump

UniK

Light kernel

Microkernel