Linux Fu: Fake Webcams, GUI Edition

Previously, I looked at using the Linux video loopback system from the command line. The basic trick was simple enough: capture video from a real camera, process it with something like ffmpeg, and write the result to a fake camera device via the v4l2loopback device. Then a browser, or any camera-enabled software, sees the fake camera as if it were real. This allows you to manipulate video before sending it to the rest of the world.

That works, and for those of us who like command lines, it’s easy enough to execute. But not everyone loves the command line. In the comments, there was another obvious answer: use OBS Studio.

While OBS is excellent, it is also a bit like using a laser to chop a carrot. If you already use OBS, fine. If you only want to crop a webcam, add an effect, mirror an image, or feed a virtual camera, it can feel like a lot. If you must have a GUI, you can try Webcamoid, which sits somewhere between a simple webcam viewer and a full video production system.

Webcamoid gives you a GUI for selecting a camera, applying effects, and sending the result to a virtual camera. Conceptually, it is much closer to the command-line loopback setup from the previous post than to OBS. You are still building a pipeline from input camera to output camera, but now you can do much of it with buttons and menus instead of shell commands.

That’s in theory, of course. Implementing Webcamoid turned out to be quite the exercise. Granted, this probably varies depending on where you install software. If your distro has a clean working copy of Webcamoid and its dependencies, good for you. For everyone else, keep reading.

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Linux Fu: Taming Strace

While many operating systems seem to try to prevent you from peeking under the hood, Unix and Linux positively encourage it. One great tool that we’ve looked at before is strace. Using this tool, you can see details about every system call a program makes. As you might imagine, for any significant program, the output from strace can be huge.

While I’m not always a fan of GUIs, this is one of those cases where making the data easier to browse is a great idea. Enter strace-tui, a text-based GUI for strace from [Rodrigodd]. The program can parse output from strace or manage the strace execution itself, and either way, display the data in a useful way.

I started out looking at [janestreet’s] strace_ui, but the OCaml setup was throwing errors for me, so I just gave up. The strace-tui installs like many Rust programs, using cargo, and it went smoothly.

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Linux Fu: Fake Webcams Have Many Uses

Dealing with text streams is a fundamental skill for the Linux power user. You can sort, merge, and search text files easily from the command line. What if you could do the same thing with video? Well, you can. Maybe you want to add a logo to a webcam feed before sending it to a conference app. Maybe you want to blur, color-correct, or annotate video in real time. Or perhaps you want to inject prerecorded video into Zoom while pretending it is a live camera. Linux can do all of this, and the key ingredient is usually the same: a loopback video device.

The basic idea is simple. Instead of an application reading directly from /dev/video0, you create a fake camera device using the v4l2loopback kernel module. Your software pipeline writes processed video into the fake camera, and applications read from it as if it were a normal webcam. The result is surprisingly powerful.

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Linux Fu: The Bluetooth Regression

There’s a line in a [Weird Al] (no relation) song that says, “I upgrade my system at least twice a day…” I know how that is. I primarily use a rolling distro, OpenSuse Tumbleweed, and if I’m having a problem that I’m too lazy to run down, it is extremely tempting to do an upgrade and see if it just happens to fix the problem.

Of course, the problem is often caused by a previous upgrade. Recently, I’ve been having a lot of trouble with the NVIDIA proprietary drivers, so I updated them yet again. After a huge amount of effort to sort out the video problems, I found that the latest kernel didn’t like my MediaTek Bluetooth adapter, which is built into the motherboard’s WiFi chipset.

This post isn’t about how to fix your Bluetooth problem. You probably don’t have the same setup I do, and even if you do, it will be sorted out in a week or two anyway. But how I temporarily fixed this issue is worth documenting. The details are going to apply to Tumbleweed and this particular adapter, but the general approach should work anywhere with any sort of kernel module problem.

My Own Fault

Part of my problem is my own fault, of course. I have a complex disk setup and do not use the recommended btrfs root file system. That means I can’t do the snapshot thing where I can just undo a bad upgrade. If I did, then sure, I should just roll back and wait for an upstream fix.

I do have “normal” backups, but they are not always totally up to date. Worse, I have found that for things like NVIDIA, the user stuff and the kernel module stuff have to match up. That makes it very hard to roll back a kernel with older modules. The modules themselves live with the kernel, but the user space stuff gets pushed out. Or, if you uninstall things, it uninstalls it for all kernels.

Truthfully, NVIDIA and others like that should keep all the user space stuff in a kernel-specific place, and then symlink it at boot to /usr/bin or wherever. But they don’t. In the end, I didn’t want to go through the trouble of rolling things back and decided to push ahead.

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Linux Fu: The USB WiFi Dongle Exercise

The TX50U isn’t very Linux-friendly

If you’ve used Linux for a long time, you know that we are spoiled these days. Getting a new piece of hardware back in the day was often a horrible affair, requiring custom kernels and lots of work. Today, it should be easier. The default drivers on most distros cover a lot of ground, kernel modules make adding drivers easier, and dkms can automate the building of modules for specific kernels, even if it isn’t perfect.

So ordering a cheap WiFi dongle to improve your old laptop’s network connection should be easy, right? Obviously, the answer is no or this would be a very short post.

Plug and Pray

The USB dongle in question is a newish TP-Link Archer TX50U. It is probably perfectly serviceable for a Windows computer, and I got a “deal” on it. Plugging it in caused it to show up in the list of USB devices, but no driver attached to it, nor were any lights on the device blinking. Bad sign. Pro tip: lsusb -t will show you what drivers are attached to which devices. If you see a device with no driver, you know you have a problem. Use -tv if you want a little more detail.

The lsusb output shows the devices as a Realtek, so that tells you a little about the chipset inside. Unfortunately, it doesn’t tell you exactly which chip is in use.

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Linux Fu: Yet Another Shell Script Trick

I’m going to go ahead and admit it: I really have too many tray icons. You know the ones. They sit on your taskbar, perhaps doing something in the background or, at least, giving you fingertip access to some service. You’d think that creating a custom tray icon would be hard, but on Linux, it can be surprisingly simple. Part of the reason is that the Freedesktop people created standards, so you don’t typically have to worry about how it works on KDE vs. GNOME or any of the other desktop environments. That’s a big win.

In fact, it is simple enough that you can even make your own tray icons with a lowly shell script. Well, of course, like most interesting shell scripts, you need some helper programs and, in this case, we’ll use YAD — which is “yet another dialog,” a derivative of Zenity. It’s a GTK program that may cause minor issues if you primarily use KDE, but they are nothing insurmountable.

The program is somewhat of a Swiss army knife. You can use it to make dialogs, file pickers, color selectors, printer dialogs, and even — in some versions — simple web browsers. We’ve seen plenty of tools to make pretty scripts, of course. However, the ability to quickly make good-looking taskbar icons is a big win compared to many other tools.

Docs

Depending on what you want to do, YAD will read things from a command line, a file, or standard input. There are dozens of options, and it is, honestly, fairly confusing. Luckily, [Ingemar Karlsson] wrote the Yad Guide, which is very digestible and full of examples.

Exactly what you need will depend on what you want to do. In my case, I want a tray icon that picks up the latest posts from my favorite website. You know. Hackaday?

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Linux Fu: Compose Yourself!

Our computers can display an astonishing range of symbols. Unicode alone defines more than 150,000 characters, covering everything from mathematical operators and phonetic alphabets to emoji and obscure historical scripts. Our keyboards, on the other hand, remain stubbornly limited to a few dozen keys.

On Windows, the traditional workaround involves memorizing numeric codes or digging through character maps. Linux, being Linux, offers something far more flexible: XCompose. It’s one of those powerful, quietly brilliant features that’s been around forever, works almost everywhere, and somehow still feels like a secret.

XCompose is part of the X11 input system. It lets you define compose sequences: short key sequences that produce a Unicode character. Think of it as a programmable “dead key” system on steroids. This can be as simple as programming an ‘E’ to produce a Euro sign or as complex as converting “flower” into a little flower emoji. Even though the system originated with X11, I’ve been told that it mostly works with Wayland, too. So let’s look deeper.

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