This post is automatically translated from the Chinese version with LLM. The translation content has been edited and verified by the author. Yes, you read that right. Without the need for Faraday cages or signal-blocking measures, you can build a legal LTE network at home (in the US) for around $100, capable of transmitting continuously 24/7. Regarding "legal": I am not a lawyer or a wireless expert. Based on my research into the relevant policies and regulations, my entire setup should be legal. However, I take no responsibility if you encounter any legal issues after following the instructions in this post. CBRS Band: Unlicensed LTE/5G Band in the US The challenge in building your own LTE network lies not in the technology but in legally acquiring radio spectrum resources....

Preface The mobile phone I'm using today is Motorola Edge+ 2023, an Android phone. To better customize my phone's functionalities, I unlocked its bootloader, and obtained root privileges, in order to install LSPosed and various LSPosed based plugins. The root mechanism I'm using is KernelSU , which works by modifying the Linux kernel to grant and only grant root permissions to certain apps. Although KernelSU provides official GKI kernel images that work on most phones, I also flashed LineageOS onto my phone, which is not compatible with GKI images. Therefore, I have to compile my own kernel. Since modifying the kernel's binary image is difficult, we usually obtain the kernel source code under the GPLv2 license from the phone manufacturer, modify it according to KernelSU's official guide ,...

List of NixOS series posts: NixOS Series 1: Why I fell in love NixOS Series 2: Basic Config, Nix Flake & Batch Deploy NixOS Series 3: Software Packaging 101 NixOS Series 4: "Stateless" Operating System NixOS Series 5: Creating Disk Image for Low RAM VPS (current post) Black friday has passed. Some readers, I believe, have perchased some VPSes or cloud servers on sale, and want to install NixOS on them. However, since NixOS is nowhere as famous as popular Linux distros, such as CentOS, Debian and Ubuntu, almost no VPS provider will offer a disk image preinstalled with NixOS. This lefts the user one of the following options to perform the installation manually: Mounting NixOS's installer ISO, and then partition and install manually....

(Title image sourced from: Wikipedia - Trigonometry ) Why I wanted to calculate the network latency between all my VPS nodes, and add the latency into the configuration file of Bird BGP daemon, so the network packets are forwarded through the lowest latency route. However, I have 17 nodes as of today, and I didn't want to manually run a ping command between each pair. So I came up with a solution: I can mark the latitudes and longitudes of the physical locations of my nodes, calculate the physical distance, and divide that by half the light speed to get the approximate latencies. I randomly sampled a few node pairs, and found that the Internet routing between them are mostly straightforward, with no significant detours. In this case,...

A year ago, to simultaneously browse webpages and write codes on my Arch Linux installation and use Windows to run tasks infeasible on Linux (such as gaming), I tried GPU passthrough on my Lenovo R720 gaming laptop . But since that laptop has an Optimus MUXless architecture (as mentioned in that post), its dedicated GPU doesn't have output ports, and the integrated GPU is in charge of all the displays. Therefore, severe limitations exist for that setup, and I eventually gave up on it. But now, I've purchased a new laptop. The HDMI output port on this laptop is directly connected to its NVIDIA dedicated graphics card, or in other words, it has an Optimus MUXed architecture. Since there is a way to make the virtual machine aware of a "monitor on the dedicated GPU",...

List of NixOS series posts: NixOS Series 1: Why I fell in love NixOS Series 2: Basic Config, Nix Flake & Batch Deploy NixOS Series 3: Software Packaging 101 NixOS Series 4: "Stateless" Operating System (current post) NixOS Series 5: Creating Disk Image for Low RAM VPS Changelog: 2023-02-18: Fix config not applied to the root user, in the "Move Temp Directory of Nix Daemon" section. One of the most famous features of NixOS is that most software configurations on the system are generated and managed exclusively by a Nix-language config file. Even if such software modifies its config file while running, the config file will still be overwritten on the next Nix config switch or the next reboot. For example, if you run ls -alh /etc on a computer running NixOS,...

List of NixOS series posts: NixOS Series 1: Why I fell in love NixOS Series 2: Basic Config, Nix Flake & Batch Deploy NixOS Series 3: Software Packaging 101 (current post) NixOS Series 4: "Stateless" Operating System NixOS Series 5: Creating Disk Image for Low RAM VPS One characteristic of NixOS is that all binary applications and libraries are stored in /nix/store directory and managed by Nix package manager. This means that NixOS doesn't conform to the FHS standard of Linux , and there's not even a dynamic library loader like ld-linux-x86-64.so.2 in /lib or /lib64 , let alone other shared libraries like libc.so . Therefore, unless the program is statically linked, binaries compiled for other Linux distros will not run on NixOS at all. Therefore,...

I got a new laptop some time ago, an HP OMEN 17t-ck000. While it's a nice laptop with excellent build quality and performance, it has one problem: it's drivers under Linux are far from complete. No support for fan speed control. You can see the fan speed but that's it. In addition, HP's default fan control strategy is very agressive, in the sense that even with fan spin down enabled in BIOS, the fan keeps running with the CPU being around 40 degrees celsius and GPU being idle. Actually, NBFC can be used to control the fan speed by directly writing to EC registers, but in an unfortunate accident I lost my configuration file. I was trying NixOS on my new laptop when I set up NBFC. When the accident happened, I had removed NixOS from the laptop,...

Changelog 2022-07-21: Add starting GVT-g on startup. Thanks to comment from Owsmyf (on Chinese version of this post). 2022-01-22: Revisions on NVIDIA driver updates and comments. I successfully passed through an Optimus MUXed GPU on my new laptop. Abstract (Spoiler Alert!) I successfully passed through Intel's GVT-g virtual GPU, as well as the dedicated NVIDIA GPU itself, into a virtual machine on Lenovo R720 gaming laptop. However, due to the limitation of the architecture itself, this GPU passthrough scheme is severely limited. For example, the dGPU is unusable in many games, and the performance is still relatively worse despite the complicated setup it needs. Therefore, you may attempt the passthrough purely for the fun of tinkering,...

Welcome to my third development log. In the two previous logs, I discussed the pitfalls I met in the RoboMaster competition and FPGA course final project . This time I will be talking about my graduate design project, an air quality sensor network built by a 3-person group. The whole project is structured as follow: Obtain data from installed sensor modules and upload them to InfluxDB running on a server Sensors we used: MiCS6814, measures NO2, CO, and NH3 Analog output BME680, measures temperature, humidity, atmospheric pressure, and TVOC I2C interface PMS5003, measures particle matters UART serial output Extra modules: ATGM336H, global positioning module with GPS+BeiDou support UART serial output ESP8266, a widely used Wi-Fi module UART serial output MH-CD42,...