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Custom Application Sandbox

I’ve been using Fedora Silverblue as my daily driver for a while now. Over time, I’ve fully adopted Flatpak, which I really enjoy using alongside Flatseal. I particularly appreciate how Flatpak gives each application its own isolated directory structure, making backups incredibly straightforward. However, I eventually hit a wall when it came to proprietary GPU drivers for workloads like media decoding, 3D rendering, and running local LLMs. In these scenarios, Flatpak’s runtime abstraction can sometimes become a liability. While this can sometimes be solved by enabling the Flathub repository or installing custom packages, I wanted to avoid that route. After comparing various alternatives, I decided to write my own lightweight application launcher. The Problem Flatpak achieves portability by bundling apps inside standardized runtime environments (like the Freedesktop or GNOME runtimes). While this solves the “dependency hell” of the 2000s, it introduces a subtle friction point for he...
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Qubesify My Daily Driver Part 3: VM Management, Nested Compositors, and Containment

In Part 2 , I got a basic proof-of-concept running: a single headless microVM booting a minimal Debian kernel and forwarding Firefox back to my daily-driver desktop (“Viewer VM”) over VSOCK using Waypipe and PipeWire. It proved the concept, but it was essentially a static, single-instance test rig. To actually live in this setup like I used to in Qubes OS, I needed to turn this prototype into a scalable, multi-domain system. In this post, I’ll walk through the next iteration of the architecture: building a centralized VM lifecycle manager, isolating VMs under dedicated host users, scaling dynamic TAP networks, and running the Waypipe viewer inside a confined nested compositor container. 1. Domain Modeling & Host VM Management In Qubes OS, workloads are categorized into Disposable VMs (DispVMs) for ephemeral tasks and AppVMs for persistent user data, both derived from centralized Template VMs . While Qubes relies on Template VMs to maintain packages across domains, I chose ...
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Qubesify My Daily Driver Part 2: Headless Micro VM

I decided to take the plunge into micro VMs. My goal? To set up a headless micro VM capable of running graphical programs remotely. As a first milestone, I wanted to get Firefox running and smoothly playing videos. (See Part 1 for a breakdown of why I passed on other isolation methods.) Overview At a high level, the concept is simple: I click an icon, and Firefox opens seamlessly on my screen while actually running securely in a VM. This setup is similar to disposable VMs in Qubes OS. When the program closes, the VM is destroyed, leaving absolutely zero trace on the disk. To pull this off, I needed to boot a micro VM with a minimal kernel and disk image, and seamlessly forward both graphics and audio to my daily-driver main VM. The Kernel Unlike standard VMs, micro VMs do not support PCI devices. Instead, they rely on different protocols (like virtio_mmio and virtio_blk ), which the kernel must support natively. Crucially, these drivers must be compiled directly into the kernel...
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Isolating Graphical Software (Part 1)

I’ve really been missing the experience of Qubes OS, where all programs are properly isolated. However, I can’t install it on my daily driver because I use that machine for gaming. Instead, I’ve been exploring ways to approximate that isolation on a standard Linux setup. Firefox Profiles Let’s start with the browser. There are many privacy and security benefits to separating profiles. My general workflow is as follows: I create separate .desktop files to run Firefox with different profiles. Each file uses a unique --name and StartupWMClass= . This prevents the icons from stacking together on the GNOME Panel. I use ImageMagick to tint the icons so I can tell the profiles apart at a glance: magick input.png -colorspace gray -fill "#cc0000" -tint 100 output.png The “new” Firefox profile manager didn’t work well for me. For example, I couldn’t set a default profile for opening external URLs. I eventually had to switch back to the old profile management style. However, whil...
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My Experience with libvirt

My daily driver setup has been working exceptionally well. If you missed them, you can check out the previous posts for details: Part 1 Part 2 Part 3 Recently, I decided to harden my setup by writing custom AppArmor profiles and nftables rules. During my research, libvirt kept popping up in tutorials. In fact, most “QEMU/KVM” guides simply assume you are using it. Initially, I decided against using libvirt because I wasn’t a fan of its design philosophy. However, I kept hearing that it can automatically generate AppArmor profiles and firewall rules for each VM. Furthermore, this article highlighted several things that libvirt genuinely simplifies. Intrigued, I decided to dive in and get some first-hand experience. The plan was to migrate my existing VM setup (which relies on bare QEMU scripts) to libvirt to see if it was a good fit. I specifically wanted to evaluate the parts of libvirt I was previously skeptical about: Reliance on a highly privileged daemon. Configuration stored...
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Fix a USB Game Controller Disconnecting When Idle

I have a USB game controller that works flawlessly during gameplay, but it keeps disconnecting and reconnecting every ~40 seconds whenever it is left idle. While it is mostly harmless in practice, it is annoying to see the kernel messages are flooded with messages about the game controller. Many online resources, such as the Arch Wiki , suggest disabling USB autosuspend to fix this. Unfortunately, that didn’t solve the issue in my case. I suspect the controller expects to be continuously polled rather than entering a power-saving state, especially since it immediately tries to reconnect after dropping. Since I primarily use this controller by passing it through to a VM, I needed a way to manually manage its connection state. Here is the workaround that eventually did the trick: Add the following rule to udev . This ensures the controller is ignored by the host system upon connection. ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="xxxx", ATTR{idProdu...
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Linux Daily Driver Setup Part 3: VM Control Panel

Now that I have my VMs running, what if I want to switch between them? What if I want to put the VM or the host to sleep, or shut them down? In this post, I’ll discuss a few options. Just a quick overview of my setup: Only one VM is running at a time. All VMs have GPU passthrough, and the GPU is connected to a display. I have a secondary display, which I prefer not to use unless absolutely necessary. See also: Part 1 Part 2 Option 1: Deep Integration with Guest OS Ideally, I could just click on a “Power off and Switch to VM X” menu from within the guest OS. This isn’t difficult to support on the host side: the guest OS could pass the VM name to the host (e.g., via a serial port), and the host would automatically start the next VM when the current one exits. However, I didn’t find an easy way to implement this menu, especially considering I plan to support multiple operating systems. I also couldn’t find a way to prevent the guest from shutting down without providing the next V...
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