Linux Hacks

535 Articles

Build Your Own Bootable Emacs Environment

April 22, 2023 by 18 Comments

An old joke is that Emacs is a text editor with an operating system included, given that its extensibility and customization often goes far beyond traditional text editors. Part of its well-earned reputation comes from being built in Lisp which allows it to be expanded to do almost anything. Despite this in-joke in the community, though, you will still need an actual operating system to run it, but not much more than that.

This project uses User-Mode Linux (UML) as a foundation to load almost nothing other than an Emacs editor. UML is a virtualization technology that allows running multiple Linux kernel instances as separate virtual machines, so once the Linux environment is started and Emacs is compiled, the virtual machine can essentially boot straight into an Emacs environment. Some tools are needed outside of the Linux kernel like mount which allows the virtual file system to access the files needed to build Emacs, but as far as lightweight or minimalist Linux distributions go this one definitely gets at least an honorable mention.

While UML is virtualization software rather than a full-fledged Linux distribution, we would expect a similarly minimalist build could easily be done with something more hardware-based like Linux From Scratch. Emacs has been around for so long and had such a wide reach that it’s difficult to imagine a world without it. Even in more modern technology like browsers, knowing a little bit about Emacs can be an extremely powerful tool.

Before You Sudo Rm -rf /, Take Some Precautions

April 21, 2023 by 40 Comments

Maintaining or administering a computer system remotely is a common enough task these days, but it’s also something that can go sideways on you quickly if you aren’t careful. How many of us are guilty of executing a command, having it fail, and only then realizing that we weren’t connected to the correct computer at all? [Callan] occasionally has this issue as well, but in at least one instance, he deleted all of the contents of the wrong server by mistake. To avoid that mistake again, he uses color codes in the command line in a fairly unique way.

The solution at first seems straightforward enough. Since the terminal he’s using allows for different colors to be displayed for the user and hostname on the bash prompt, different text and background colors are used for each server. The only problem with this is that his friends also have access to these servers, and one of them is red/green colorblind, which led to another near-catastrophic mix-up. To ensure no edge cases are missed, [Callan] built a script which runs on every new server he spins up which selects two random colors, checks that they contrast well with each other, don’t create problems for the colorblind, and then applies them to the bash prompt.

For a problem most of us have had at some point or another, it’s a fairly elegant solution that helps ensure we’re sending the right commands to the right computer. This adds a layer of automation to the process and, while some color combinations do look similar, there are enough to help out most of us in some way, especially since he has released the source code on his GitHub page. For other helpful server administration tips, we’d recommend the Linux-Fu article about deploying your own dynamic DNS.

Linux Server, Wakey, Wakey

April 21, 2023 by 39 Comments

We all know we should save energy and not leave computers on all the time. It is probably better for the computer, too. But when you operate a home server, it isn’t feasible to just turn it on when you want to use it and then turn it off again. Or is it? [Daniel] decided that was exactly what he wanted to do, and it was quite an adventure to get there.

The trick is to use a Raspberry Pi — they don’t draw nearly the power a big computer does — to stay awake to facilitate the process. The Pi watches for ARP requests for the sleeping machine and replies on its behalf so that other network nodes can find the machine even when it isn’t on.

The server itself detects if it is idle in a cron job. When it finds that there are no SSH or other service connections for a set period of time, it suspends the machine to RAM, putting it in a low-power mode. Waking a sleeping computer up over the network is a solved problem, and [Daniel] investigated several wake-on-lan solutions.

There were several oddities to work out, including a Mac pinging an unused network share, and a router that was making NetBIOS queries. However, [Daniel] found a $30 router that could do port mirroring and that helped a lot with troubleshooting.

This is one of those things where his recipe won’t exactly fit your situation. But the post has a lot of good information and some nice tricks for troubleshooting any kind of network bizarreness.

Wireshark is a great tool for this kind of work, too. Another useful technique is recording network traffic and playing it back.

Linux Fu: Reading Your Memory’s Memory

April 18, 2023 by 18 Comments

Linux users have a lot of software to be proud of. However, there is the occasional Windows program that does something you’d really like to do and it just won’t run. This is especially true of low-level system programs. If you want to poke around your CPU and memory, for example, there are tons of programs for that under Windows. There are a few for Linux, but they aren’t always as complete or handy. Recently, I had half the memory in my main desktop fail and I wanted to poke around in the system. In particular, I wanted to read the information encoded in the memory chips configuration EEPROM. Should be easy, right? You’d think.

Not Really Easy

One nice tool a lot of Windows users have is CPU-Z. Of course, it doesn’t run on Linux, but there is a really nice imitator called CPU-X. You can probably install it from your repositories. However, the GitHub page is a nice stop if for no other reason than to enjoy the user name [TheTumultuousUnicornOfDarkness]. The program has a gtk or an ncurses interface. You don’t need to run it as root, but if you press the “start daemon” button and authenticate, you can see some extra information, including a tab for memory.

Continue reading “Linux Fu: Reading Your Memory’s Memory” →

Screenshot of the demonstration video that shows the desktop being unlocked with face recognition, with a camera feed and a terminal showing how the software works.

Open-Source FaceID With RealSense

April 4, 2023 by 6 Comments

RealSense cameras have been a fascinating piece of tech from Intel — we’ve seen a number of cool applications in the hacker world, from robots to smart appliances. Unfortunately Intel did discontinue parts of the RealSense lineup at one point, specifically the LiDAR and face tracking-tailored models. Apparently, these haven’t been popular, and we haven’t seen these in hacks either. Until now, that is. [Lina] brings us a real-world application for the RealSense face tracking cameras, a FaceID application for Linux.

The project is as simple as it sounds: if the camera’s built-in face recognition module recognizes you, your lockscreen is unlocked. With the target being Linux, it has to tie into the Pluggable Authentication Modules (PAM) subsystem for authentication, and of course, there’s a PAM module for RealSense to go with it, aptly named pam_sauron. This module is written in Zig, a modern C-like language, so it’s both a good example of how to create your own PAM integrations, and a path towards doing that in a different language for once. As usual, there’s TODOs, like improving the UX and taking advantage of some security features RealSense cameras have, but it’s nevertheless a fun and self-sufficient application for one of the F4XX-series RealSense cameras in case you happen to own one.

Ever since the introduction of RealSense we’ve seen these cameras used in robotics and 3D scanning, thanks at least in part due to their ability to be used in Linux. Thankfully, Intel only discontinued the less popular RealSense cameras, which didn’t affect the main RealSense lineup, and the hacker-beloved depth cameras are still available for all of our projects. Wondering about the tech behind it? Here’s a teardown of a RealSense camera module intended for laptop use.

Linux Fu: Gum Up Your Script

March 29, 2023 by 11 Comments

We often write quick bash scripts and judging by the comments, half of us use bash or a similar shell to pop out quick, useful scripts, and half of us think that’s an abomination, and you should only use bash for your command line and resort to something more like a traditional language to do anything else. If you’re in the former camp, you’re probably cursing your allegiance when you need to make your bash scripts more interactive.

Gum can help. It’s a utility that can handle your script input and output with a little flair while requiring almost no effort on your part.

The command looks simple, but it has twelve subcommands, each with myriad options. But you can break down the functions into a few simple categories. The input commands let you prompt for a line of input or a bunch of lines of input. You can also create a pick list or a yes/no type of prompt. There’s also a file picker and a filter, sort of like fzf.

Continue reading “Linux Fu: Gum Up Your Script” →

A Pi Pico soldered onto a custom breakout PCB, with an SD card connected to it using prototyping wires

RP2040 Runs Linux Through RISC-V Emulation

March 19, 2023 by 27 Comments

We’re used to running Linux on CPUs where it belongs, and the consensus is that RP2040 just isn’t up for the task – no memory controller, and nowhere near enough RAM, to boot. At least, that’s what you might believe until you see [tvlad1234]’s Linux-on-RP2040 project, reminding us there’s more than one way to boot Linux on a CPU like this! Just like with the “Linux on AVR” project in 2012 that emulated an ARM processor, the pico-rv32ima project emulates a RISC-V core – keeping up with the times.

Initially, the aforementioned “Linux on AVR through ARM” project was picked as a base – then, a newer development, [cnlohr]’s RISC-V emulator, presented itself and was too good to pass up on. Lack of RAM was fully negated by adding an SD card into the equation – coupled with a small caching layer, this is a crucial part for the project’s not-so-secret sauce. A fair amount of debugging and optimization later, [tvlad1234] got Linux to run, achieving boot times in 10-15 minutes’ ballpark – considering the emulation layer’s presence, this is no mean feat.

At this point, the boot process stalls as you enter a login shell. If Linux on RP2040 is within your area of interest, feel free to pick up the effort from here, as the project is fully open-source – you only need a Pi Pico board and a throwaway SD card! Now, if pairing a RP2040 with some classic software is your definition of an evening well-spent, you can’t go wrong with DOOM! However, if you’d rather play with something else *nix-like, we’ve seen someone port Fuzix onto the RP2040 before.