Flatpak apps on an unrooted Android phone, no user namespaces: how Tessera does it

[u/D4r13n0]

Flatpak needs bubblewrap, bubblewrap needs user namespaces, and Android kernels ship without them. So flatpak run can't work on a phone, root or not.

In Tessera (GPL-3.0, an Android app that runs Linux desktop apps as native Android windows), flatpak still downloads, but Tessera builds each app's root itself:

- the runtime at /usr and the app at /app, read-only;

- the runtime's GL extension where the runtime expects it, on a tmpfs over its parent since the folder doesn't exist in the read-only runtime;

- /etc from the runtime, with passwd, group, hosts and resolv.conf written for the session;

- the session's X11 directory shared, carrying its D-Bus and PulseAudio sockets, so the app gets the same bus, sound and theme portal as the Debian side.

Without root that's PRoot's path translation. With root, each launch gets a private mount namespace, an unprivileged uid and no_new_privs, so per-app permissions are kernel-enforced.

The rest is about making Linux apps feel native on a phone: each app (and each of its windows) gets its own Android task and Recents card; GTK, libadwaita and Qt take Material You colors and follow dark mode live through a settings portal Tessera serves; apps rescale live from a slider; and the Android keyboard opens on text fields by listening to AT-SPI focus events. GPU acceleration is a bundled Mesa with Turnip and Zink for Adreno, which also loads inside Flathub runtimes.

Source: https://github.com/daryan044/tessera-linux

Note: AI WAS USED IN THE PROCCESS OF CREATING THIS APP

Happy to go deeper on any part.

[u/valgrid]

Would this work on Linux PRoot Container (like Linux Labs) too?

[u/D4r13n0 → u/valgrid]

The app itself has two containers, proot and chroot, it mimics the bubble wrap not run it

[u/Busy-Scientist3851]

I wish GoogleBookOS supported Flatpak natively, would honestly become super enticing