Distribution Agnostic Linux Applications

Cover image created by Kirokaze

I’m very…passionate about maintaining a clean OS environment. I can’t count the number of times I’ve installed a desktop application only for it to use up an inordinate amount of resources, clutter up my filesystem by writing files everywhere or break the dependencies of other applications. I’ve even (misguidedly) gone as far as creating VMWare virtual machines for different workloads to emulate workspace segmentation and mitigate these issues. Kind of like a janky Qubes OS minus the hardened security profile . Fortunately, several developers felt the same way and developed platforms that lead the way for distribution-agnostic software packaging, namely Flatpak , Snap and AppImage . While the primary goal of these projects is to provide universal software packaging for all Linux distributions, the features I gush about are the security sandboxing profiles and clean installation methods that become a reality using these three platforms.

…ok, maybe not all three of them. Let me explain.

Player 1: Snap

Snap is a bit of a conundrum for me. While this platform has some good things going for it by way of leveraging Apparmor profiles to provide sandboxing and a solid list of software publisher support due to Cannonical’s backing, the need for another daemon (running as root, no less) rubs me the wrong way. Besides, many popular software installations require the --classic flag to be passed, essentially removing the confinement profiles and installing applications in nearly the same context as a distribution’s package manager without the trust model. Whoops, can’t forget that the snapd daemon calls home several times a day to check for updates. I mean, that must be what it’s doing now in my Dev-VM since it’s using up 13G of virtual memory on idle. I think I’ll just systemctl disable --now snapd.service snapd.socket and activate this guy on a case by case basis.

…and for anyone thinking (you know who you are), yes it IS ironic that a dude who talks highly about clean operating system environments and software segmentation enjoys using systemd . J-just…do me a solid and finish reading the post before you crucify me, mmkay? Thanks ;).

Player 2: Flatpak

The beginning of this year saw me riding the Flatpak bandwagon heavy. I’d just installed Fedora to bare-metal for the first time and the shiny of it all had me sold. I do admit, Fedora’s work on immutable filesystems and integration with Flatpak in Silverblue is pretty impressive. Then I had a bomb dropped on me when I read Flatkill . Realizing that bubblewrap application sandboxing is left up to the developer and is not the default shook me. Many of the Flatpaks I’d installed up to that point we’re most likely out of date and had serious vulnerabilities. To be honest, this is most likely the event that sent me down this universal application packaging rabbit hole and further reinforced my scrutiny for alternative software installation sources (I’m looking at you, every AUR helper in the world). To be honest, it was time for a distro hop anyways.

Enter AppImage

This brings us to our final contestant, AppImage . Even though AppImage received the proverbial Linus Torvalds seal of approval, the platform seems heavily slept on by major software developers. By far the most attractive feature of the AppImage platform is the single-binary approach it takes. In comparison to Flatpak which installs multiple application files in /var/lib/flatpak for system-wide installs and $HOME/.local/share/flatpak/app/ for user installations and Snap which does the same in /snap for system-wide, $HOME/snap for local installations and creates symlinks in /usr/bin/snap (clutter, clutter, clutter!), Flatpak just gives you a single binary that you can chmod a+x, throw in a directory that lies on your PATH (/usr/local/bin for system-wide or ~/.local/bin for user installs) and execute directly from the terminal. Running file against an appimage gives results for your run-of-the-mill 64-bit ELF.

$ ~/.l/bin file LibreOffice-fresh.standard-x86_64.AppImage
LibreOffice-fresh.standard-x86_64.AppImage: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-Linux-x86-64.so.2, for GNU/Linux 2.6.18, stripped

I previously mentioned Flatpak and Snap’s intermittently used sandbox implementations. In AppImage’s case there are no integrated default sandboxing implementations. While running Appimages without a sandboxing implementation could be a risky venture, having the freedom to choose which sandboxing implementation to use and the control to customize whitelist/blacklist profiles far outweigh the convenience that comes with having a preset default. That opens the doors for using nsjail or firejail in conjunction with mandatory access control systems like SELinux or AppArmor for added security.

A covert benefit to having an invasive daemon like snapd playing Jeff Bezos with your system resources is being able to easily launch an application from your desktop environment’s shell. For that we have appimaged , a daemon (itself in the form of an AppImage) programmed to monitor directories in your path for AppImages and register them with the system upon discovery. This daemon can also be run with firejail and apparmor confinement and in the context of a user instead of as root; then, to top it off we can add in AppImageUpdate for easy updates to compatible AppImages. Pretty neato.