Ritiek Malhotra ritiek

GROKKING NOTES

I liked the way Grokking the coding interview organized problems into learnable patterns. However, the course is expensive and the majority of the time the problems are copy-pasted from leetcode. As the explanations on leetcode are usually just as good, the course really boils down to being a glorified curated list of leetcode problems.

So below I made a list of leetcode problems that are as close to grokking problems as possible.

Pattern: Sliding Window

Think twice before abandoning Xorg. Wayland breaks everything!

Hence, if you are interested in existing applications to "just work" without the need for adjustments, then you may be better off avoiding Wayland.

Wayland solves no issues I have but breaks almost everything I need. Even the most basic, most simple things (like xkill) - in this case with no obvious replacement. And usually it stays broken, because the Wayland folks mostly seem to care about Automotive, Gnome, maybe KDE - and alienating everyone else (e.g., people using just an X11 window manager or something like GNUstep) in the process.

Update 06/2025: X11 is alive and well, despite what Red Hat wants you to believe. https://github.com/X11Libre/xserver revitalizes the Xorg X11 server as a community project under new leadership.

Encrypted Btrfs storage setup and maintenance guide

Initial setup with LUKS/dm-crypt

This exemplary initial setup uses two devices /dev/sdb and /dev/sdc but can be applied to any amount of devices by following the steps with additional devices.

Create keyfile:

dd bs=64 count=1 if=/dev/urandom of=/etc/cryptkey iflag=fullblock
chmod 600 /etc/cryptkey

Linux Kernel Modules for NixOS

You can find what kernel modules are loaded using lsmod.

However some kernel modules are required at stage 1 boot. Basically preloaded in the initial ram disk before switching to the root filesystem. These kernel modules are mostly needed to deal with peripherals, storage devices, filesystems and network devices. You may need to be wary of these required modules:

sd_mod - SCSI, SATA, and PATA (IDE) devices

Open a webpage that uses the CA with Firefox
Click the lock-icon in the addressbar -> show information -> show certificate
the certificate viewer will open
click details and choose the certificate of the certificate-chain, you want to import to CentOS
click "Export..." and save it as .crt file
Copy the .crt file to /etc/pki/ca-trust/source/anchors on your CentOS machine
run update-ca-trust extract
test it with wget https://example.com

On Manjaro (arch) the location for the certificates is: /usr/share/ca-certificates/trust-source/anchors (low priority) or /etc/ca-certificates/trust-source/anchors/ (high priority) and the command to update is update-ca-trust extract.

After installing mitmproxy run it (just type mitmproxy) in a terminal session and quit. This will create the necessaries certificates files at ~/.mitmproxy.
Extract the certificate to .crt format:
openssl x509 -in ~/.mitmproxy/mitmproxy-ca.pem -inform PEM -out ca.crt
Trust the certificate into CA:
sudo trust anchor ca.crt
Run the mitmproxy again

Running Windows software on the Raspberry Pi (and other ARM devices) with Wine

	{ lib, buildUBoot, fetchFromGitHub, armTrustedFirmwareRK3328 }:
	let
	rkbin = fetchFromGitHub {
	owner = "ayufan-rock64";
	repo = "rkbin";
	rev = "f79a708978232a2b6b06c2e4173c5314559e0d3a";
	sha256 = "0h7xm4ck3p3380c6bqm5ixrkxwcx6z5vysqdwvfa7gcqx5d6x5zz";
	};
	in buildUBoot {
	extraMakeFlags = [ "all" "u-boot.itb" ];

	#include <SDL2/SDL.h>
	#include <cstdio>
	#include <list>
	#include <signal.h>

	std::list<std::pair<SDL_Joystick, SDL_Haptic>> joysticks;

	void shutdown_joysticks() {
	SDL_Log("Closing joysticks");
	for (std::pair<SDL_Joystick, SDL_Haptic> joystick : joysticks) {

	ffmpeg -f x11grab -thread_queue_size 64 -video_size 1920x1080 -framerate 30 -i :1 \
	-f v4l2 -thread_queue_size 64 -video_size 320x180 -framerate 30 -i /dev/video0 \
	-filter_complex 'overlay=main_w-overlay_w:main_h-overlay_h:format=yuv444' \
	-vcodec libx264 -preset ultrafast -qp 0 -pix_fmt yuv444p \
	video.mkv