Always Set Zoom Level for a Webcam

	# /etc/udev/rules.d/99-local-webcam.rules
	# Logitech C925e webcam zoom
	SUBSYSTEM=="video4linux", SUBSYSTEMS=="usb", ATTRS{idVendor}=="046d", ATTRS{idProduct}=="085b", PROGRAM="/usr/bin/v4l2-ctl --set-ctrl zoom_absolute=150 --device /dev/%k"

view raw 99-local-webcam.rules hosted with ❤ by GitHub

XDG Base Directory Compliant ~/.python_history

	# Store interactive Python shell history in ~/.cache/python_history
	# instead of ~/.python_history.
	#
	# Create the following .config/pythonstartup.py file
	# and export its path using PYTHONSTARTUP environment variable:
	#
	# export PYTHONSTARTUP="${XDG_CONFIG_HOME:-$HOME/.config}/pythonstartup.py"
	import atexit
	import os
	import readline
	histfile = os.path.join(os.getenv("XDG_CACHE_HOME", os.path.expanduser("~/.cache")), "python_history")
	try:
	readline.read_history_file(histfile)
	# default history len is -1 (infinite), which may grow unruly
	readline.set_history_length(1000)
	except FileNotFoundError:
	pass
	atexit.register(readline.write_history_file, histfile)

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ZTE Speedport Entry 2i Key Generator

	#!/usr/bin/env python
	#
	# ZTE Speedport Entry 2i Key Generator
	#
	# The script generates the key for decryption and encryption
	# of ZTE Speedport Entry 2i configuration file using
	# https://github.com/mkst/zte-config-utility
	#
	# Usage:
	#
	# ./zte-speedport-entry-2i-key-generator.py
	# MAC address: c85a9fa21821
	# Serial: 268EG8JL4M16271
	# Factory SSID: ZTE-ABCDEF
	# Factory WLAN Key: zxcvbnmasdfg
	# Factory Username: admin
	# Factory Password: qwertyui
	# Hardware Version: V1.0.1
	# ade8b5e3e9c57a5f
	#
	# Configuration decryption:
	#
	# PYTHONPATH=./zte-config-utility
	# python ./zte-config-utility/examples/decode.py config.bin config.xml --key ade8b5e3e9c57a5f
	#
	# Configuration encryption:
	#
	# PYTHONPATH=./zte-config-utility
	# python ./zte-config-utility/examples/encode.py config.xml config.bin --key ade8b5e3e9c57a5f --signature "Speedport Entry 2i"
	from hashlib import md5
	l = lambda s: len(s).to_bytes(3, "little")
	a = lambda s: s.encode("ascii")
	mac = int(input("MAC address: "), 16)
	serial = a(input("Serial: "))
	ssid = a(input("Factory SSID: "))
	wlan_key = a(input("Factory WLAN Key: "))
	username = a(input("Factory Username: "))
	password = a(input("Factory Password: "))
	mac_zte = a("54BE53")
	version = a(input("Hardware Version: "))
	zero = a("0")
	print(md5(
	b"\x01\x00\x00\x06\x00\x00" + (mac).to_bytes(6, "big") + \
	b"\x01\x01\x00\x06\x00\x00" + (mac + 1).to_bytes(6, "big") + \
	b"\x01\x02\x00\x06\x00\x00" + (mac + 2).to_bytes(6, "big") + \
	b"\x01\x03\x00\x06\x00\x00" + (mac + 3).to_bytes(6, "big") + \
	b"\x02\x00\x00" + l(serial) + serial + \
	b"\x04\x00\x00" + l(ssid) + ssid + \
	b"\x05\x10\x00" + l(wlan_key) + wlan_key + \
	b"\x06\x01\x00" + l(username) + username + \
	b"\x07\x01\x00" + l(password) + password + \
	b"\x03\x00\x00" + l(mac_zte) + mac_zte + \
	b"\x08\x06\x00" + l(version) + version + \
	b"\x08\x07\x00" + l(zero) + zero
	).hexdigest()[:16])

view raw zte-speedport-entry-2i-key-generator.py hosted with ❤ by GitHub

GPT Backup and Restore

	# GPT Backup
	sudo sgdisk --backup=nvme0n1.gpt /dev/nvme0n1
	# GPT Restore
	sudo sgdisk --load-backup=nvme0n1.gpt /dev/nvme0n1

view raw gpt-backup-restore.sh hosted with ❤ by GitHub

Python’s math.prod vs functools.reduce(operator.mul)

Simple Python code performance measurement of math.prod and functools.reduce with operator.mul using timeit module.

	#!/usr/bin/env python
	# An example of Python code benchmarking.
	# In this case math.prod vs functools.reduce(operator.mul).
	# As can be seen, math.prod is almost twice as fast as the other option:
	#
	# ./timeit-test.py
	# 4.723656065994874
	# 7.586232994995953
	# 18.008398708996538
	# 31.734708059004333
	from operator import mul
	from functools import reduce
	from math import prod
	from itertools import combinations
	from random import shuffle
	from timeit import timeit
	def msolve(numbers, length):
	for c in combinations(numbers, length):
	prod(c)
	def rsolve(numbers, length):
	for c in combinations(numbers, length):
	reduce(mul, c)
	x = list(range(1000))
	shuffle(x)
	print(timeit(lambda: msolve(x, 2), number=100))
	print(timeit(lambda: rsolve(x, 2), number=100))
	print(timeit(lambda: msolve(x, 3), number=1))
	print(timeit(lambda: rsolve(x, 3), number=1))

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Proxy ARP

Enable cross connection between two segments inside the same LAN without NAT. For example an access point connected to a laptop via Wi-Fi and a Raspberry Pi connected to the same laptop via Ethernet.

	#!/bin/sh
	# Enable connection between AP and RPi without NAT
	# AP --- wifi --- laptop --- ethernet --- RPi
	# Reference: https://wiki.debian.org/BridgeNetworkConnectionsProxyArp
	# 0. Assign static IP to RPi
	# 1. Enable Proxy ARP and routing on the laptop
	echo 1 > /proc/sys/net/ipv4/conf/all/proxy_arp
	echo 1 > /proc/sys/net/ipv4/ip_forward
	# 2. Add static route for RPi on the laptop
	ip route add 192.168.1.254/32 dev eth0

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Disk Backup and Restore

An example how to backup and restore an SD card containing Raspberry Pi OS.

	# Backup
	sudo dd if=/dev/mmcblk0 count=1 bs=512 of=mmcblk0.mbr
	sudo fsarchiver savefs mmcblk0.fsa /dev/mmcblk0p1 /dev/mmcblk0p2 -v -j 4
	# Info
	fsarchiver archinfo mmcblk0.fsa
	# Restore
	sudo dd if=mmcblk0.mbr count=1 bs=512 of=/dev/mmcblk0
	sudo partprobe /dev/mmcblk0
	sudo fsarchiver restfs mmcblk0.fsa id=0,dest=/dev/mmcblk0p1 id=1,dest=/dev/mmcblk0p2 -v

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Enable TCP BBR

Speed up TCP connections be enabling TCP BBR on Arch Linux:

	# Enable TCP BBR module
	echo tcp_bbr | sudo tee /etc/modules-load.d/tcp-bbr.conf
	# Set TCP to use BBR
	sudo tee /etc/sysctl.d/99-tcp-bbr.conf > /dev/null <<'EOF'
	net.core.default_qdisc=fq
	net.ipv4.tcp_congestion_control=bbr
	EOF
	# Apply the changes
	sudo modprobe tcp_bbr
	sudo sysctl --system

view raw tcp-bbr.sh hosted with ❤ by GitHub

Turn Python into HTTP server serving local directory

	# Python 3
	sudo python -m http.server 80
	# Python 2
	sudo python2 -m SimpleHTTPServer 80

view raw python-http-server.sh hosted with ❤ by GitHub

System Benchmarking

Using OpenBenchmarking.org and Phoronix Test Suite for system benchmarking and online result comparison.

• Registering an account on OpenBenchmarking.org
• Download and install the latest Phoronix Test Suite:

  wget https://github.com/phoronix-test-suite/phoronix-test-suite/archive/v9.6.0m3.tar.gz
  tar xvf v9.6.0m3.tar.gz
  cd phoronix-test-suite-9.6.0m3/
  sudo ./install-sh
  

  In case of Raspbian or Ubuntu running on Raspberry Pi, install also additional packages:

  sudo apt install php-cli php-xml php-curl php-zip
  

• Pair your (future) benchmarks with your OpenBenchmarking.org account:

  phoronix-test-suite openbenchmarking-login
  

• Useful commands to list available test suites, test profiles, search tests and estimate test runtime:

  phoronix-test-suite list-available-suites
  phoronix-test-suite list-available-tests
  phoronix-test-suite search mp3
  phoronix-test-suite estimate-run-time pts/video-encoding
  

• Run a single or multiple benchmarks in interactive mode:

  phoronix-test-suite benchmark pts/smallpt
  phoronix-test-suite benchmark pts/encode-flac pts/encode-mp3 pts/vpxenc pts/x264 pts/x265
  

• Run a benchmark in non-interactive mode against a previously uploaded test result. Useful for running the same test on a new system to compare the results:

  phoronix-test-suite batch-setup
  phoronix-test-suite batch-benchmark 2004190-V110-RPIENCO26