Open source for phones: postmarketOS

Phones running Linux are ubiquitous these days and it has been that way since Android started working toward dominance in the smartphone market. Unfortunately, Android has slowly increased its freedom-unfriendliness and has become something of a privacy nightmare. In a talk entitled "We need an open-source phone OS" at Open Source Summit Japan 2025, Luca Weiss described the smartphone landscape and gave an overview of postmarketOS as an alternative Linux operating system for mobile handsets.

Weiss introduced himself as a software engineer at Fairphone, "which is a Dutch brand to make sustainable mobile phones". In his free time, he is a postmarketOS core contributor and a maintainer for the OpenRazer project to create Linux drivers for Razer gaming peripherals. He stressed that the talk was not being done for his employer; "these are my opinions".

Mobile phone OSes

There is a duopoly for mobile operating systems right now, he began: iOS for Apple phones and Android for phones from more than 100 manufacturers. With only a few exceptions, all of the Android phones are shipping with the proprietary Google Play Services so that the Google Play store is available. Most customers require this because they do not know where to get apps otherwise; in addition, some apps that they want are only available to phones with Google Play Services.

In order to be able to ship those services, Android phone makers must be bound by Google's rules, which is a double-edged sword. On the good side, there are some minimal security requirements for the Android version, as well as policies ensuring API compatibility for the apps. However, those manufacturers have far less independence in what they can do on their phones. It also requires a business relationship with a US company, which may be problematic for companies in some countries currently and it is unknown if those restrictions might expand over time. Beyond that, Google could change its rules at any time or even lose interest and stop providing Android source code at all.

There are multiple problem areas because there are no alternatives to that duopoly, he said. Google bundles and pushes privacy-invasive apps; his example was Google Photos, which defaults to sending photos to the Google cloud and, if that is disabled, regularly pops up messages to "warn" users that their photos are not being backed up—with a default action of re-enabling the feature to dismiss the popup.

While the Android Open Source Project (AOSP) is available under the Apache 2 license, development is done behind closed doors with releases tossed over the wall; getting code into AOSP is not impossible, he said, unless the feature does not align with Google's business interests. There is also the question of whether Android will stay open source, Weiss said. Meanwhile, installing apps that do not come from the Play store ("which they call 'sideloading'") is being restricted to apps made by developers registered with the company, which harms users who can no longer install whichever apps they want.

There is a large amount of proprietary code in any phone running Android and, even if that code was replaced with open-source software, there would still be proprietary code running in modems and other parts of the system. Android runs as user-space programs on top of the GPLv2-licensed Linux kernel, so the Android code can be released (or not) subject to the whims of Google, but the kernel code needs to be released when phones using it start shipping. Android and Linux are only running on a small part of the system-on-chip (SoC) for a phone, however; there are multiple other co-processors of various sorts (GPU, NPU, ...) that run proprietary firmware which cannot be replaced with free software because it is signed with a key that the vendor controls. Even if the signature checking is disabled, there are no efforts that he is aware of to create free alternatives for that firmware.

There are alternative Android distributions (or ROMs), such as LineageOS, /e/OS, CalyxOS, and others, Weiss said, which are more open source than stock Android, but still rely on proprietary blobs. Libraries and binaries that are shipped on stock Android are being incorporated into the community distributions. This includes GPU drivers, modem drivers, and the like, which sit between Android and the Linux kernel, but use non-standard kernel interfaces; he is not aware of any efforts to replace those components with open-source alternatives either.

Relying on those blobs means that all security updates have to come from the vendor; when the vendor stops updating a device because it is at its end of life, updates to those components will not be easily available, though they may be obtainable from updates to similar devices. Those alternative Android distributions are also reliant on Google releasing the AOSP code, which used to happen when the new code started shipping but had recently been delayed by two months. Since the talk, the company has announced that it will only be releasing AOSP code twice per year.

postmarketOS

The tagline for postmarketOS is "The Linux distribution for mobile phones and beyond...", he said to introduce the project. The goal is to make an operating system for phones with both user-space and kernel code that is fully open. PostmarketOS developers want to ensure "that the foundations are laid to actually be able to support devices for a long time"; that's possible because they are using the upstream kernel and not a fork of an older kernel. That allows updating all of the components "and if there's an incompatibility, you can actually fix it without any big issues".

The distribution is aimed at being largely generic, rather than having lots of device-specific parts. Right now, most devices have a device-specific root filesystem and boot image, but the plan is to have a single root filesystem for all devices, with just the kernel and some configuration that is customized for the device.

PostmarketOS is a volunteer-driven and donation-funded independent project, Weiss said. The donations are used to fund infrastructure, including "hacker phones to actually work on together", and to "have some stuff for the FOSDEM conference, where we're always present". It uses Alpine Linux and its package manager, so postmarketOS users "can install everything that you would ever want that is in the package repositories". On top of the Alpine base, postmarketOS provides some extra tooling, device packages, build infrastructure for creating install images, and documentation including an extensive wiki.

Android devices are based on a fork of a specific LTS kernel version that never changes for the life of the device. That lifetime is generally three years, which fits well within the lifecycle of the LTS kernels; once that is done, "you're stuck with this old Linux kernel version with millions of lines of code added and modified compared to the upstream version of Linux".

Instead of that path, postmarketOS is focused on using the upstream kernel by pulling the latest from kernel.org and adding the changes needed for specific devices. The developers are working to get the "ten to 100 patches" for each device into the upstream kernel, so that the diff gets smaller and they can more easily use the upstream kernels going forward. In addition, release candidates and linux-next can be tested to ensure that there are not any regressions and that devices will continue to function with upcoming kernel releases.

By sticking with upstream, the project gets the latest features in the kernel. "There's a lot of things happening there that are actually really cool, and there's no reason that you wouldn't want it on your phone as well". User-space components like to use the newer kernel features, so it is best not to get left behind.

Sometimes the postmarketOS developers are asked why they are not using parts of Android like some other projects do. For example, Ubuntu Touch is a contributor to the Halium project, which repackages "Android bits" and provides a translation layer that will allow Android hardware abstraction layers (HALs), such as the camera HAL, to work on top of a regular Linux user space. It will also allow binaries that are built with the Android C library (bionic) to be used from programs built with the GNU C library (glibc) via libhybris. "There are some very practical reasons for doing this", he said, because it allows relying on the hardware maker to provide a well-functioning camera driver for the hardware.

There are some downsides to that approach, however, including depending on Android updates and proprietary blobs for the functioning of the peripherals. It also would make the project dependent on a "sometimes a bit flaky layer between the Android components and the Linux components". Beyond that, it "doesn't encourage the development of native solutions", such as libcamera, which he noted had featured in the talk just prior to his. That does mean that the cameras that are supported have "quite limited" photo quality compared to, say, Ubuntu Touch, currently; the goal is to get to an acceptable photo quality while always using "100% open-source software".

Status and plans

Currently, postmarketOS "is not a finished product in any sense", Weiss said, but it is still being used. The project does not have any "report to the mothership" functionality or other analytics, so it relies on "anecdotal evidence" from social media and talking to users at conferences to get a sense for how it is being used. Some people do use postmarketOS as a daily driver phone, though some of those also carry a second phone for calls and, say, access to a banking app. "Banks are quite annoying with a lot of app requirements."

There are a lot of devices that are supported by postmarketOS: 111 in the "community" category, which covers the best-supported devices, 342 in "testing", which ranges from barely booting to mostly working for some use cases ("watching YouTube on your couch"), and 250 in the "downstream" category, which still use the Android kernel for the device. When the project began, there was little support for phone devices in the upstream kernel, so everything was in the downstream category; now the kernel supports around 450 devices, so those devices have moved to the other categories over time.

PostmarketOS is not ready for the average person at this point, he said, "but I would say that it is definitely ready for the average hacker". Those who want to hack on a phone will find it to be in good shape; even most of the phones in the testing category will boot and allow logging in via ssh. At that point, "you can do fun things with the phone". He noted that his FOSDEM 2025 talk went into more detail on device support for postmarketOS.

There are lots of plans for the future and various things being worked on, but there is no real roadmap because postmarketOS is volunteer-driven. He suggested following the blog. There are monthly progress reports posted there, which give a good sense of the progress being made. There is a big difference in what is working today compared to a year or two ago, he said.

"What can you actually do with postmarketOS today?" The first step is to install it; attendees probably already have an old phone—or can get a used one cheaply—that can run it. Once booted, the phone can be hacked on over ssh or with a GUI, such as Plasma Mobile, Phosh, GNOME Mobile, or Sxmo for a tiling-window-manager experience.

It is, after all, a Linux system, so users can do anything they might do with any other such system: run Docker containers, make a Kubernetes cluster of phones, or access USB peripherals of various sorts. The compost.party web site (which was not responding as this is written) runs on "a solar-powered old, broken phone"; postmarketOS could easily be used for something like that, he said. Other creative uses include a media-playback device, a musical instrument, or part of an audio-production system.

He noted that postmarketOS "could really use some help" on the technical side. Most of that work is on upstream projects, such as on the kernel for more hardware enablement and stability, middleware projects like libcamera or feedbackd (for haptic and visual feedback), improving the UI or adding features for various mobile GUI projects. Other possibilities are upgrading existing apps or developing new ones and helping to maintain packages in the Alpine aports repository and the postmarketOS-specific pmaports repository. Much of that work can be done from desktop Linux and some of it will not just improve mobile Linux or postmarketOS, but also Linux running on larger systems.

The project also welcomes contributions from non-developers, Weiss said, and there are many different ways to do so. If they are "tech curious", contributors could install postmarketOS on a phone; if they encounter any problems in doing so, they should point out where the documentation was inadequate—or propose updates to fix it. Translations for the user interfaces and apps would help as would getting the word out about the project in diverse spaces—including ones catering to non-technical people. Contributors can help out with the monthly blog posts, the podcast, which has languished a bit due to lack of time, or on applying for funding grants in different parts of the world.

Weiss took a few audience questions after completing his talk. One asked about a "golden device" that he would recommend for those who want to start working with postmarketOS. The OnePlus 6 and 6T were long recommended by the project, he said, but those are getting old enough they are hard to find in the used marketplace; the Pixel 3a is well-supported, as is the Fairphone 5. He suggested consulting the devices page on the wiki (linked above), which can help narrow things down based on which peripherals (camera, NFT, etc.) were most needed.

Interested readers may want to check out the YouTube video of the talk and Weiss's slides.

[ I would like to thank the Linux Foundation, LWN's travel sponsor, for assistance with traveling to Tokyo for Open Source Summit Japan. ]