DSU Sideloader

DSU Sideloader lets you try a different Android system without replacing yours. It is a front end for Dynamic System Updates (DSU), a feature Android added in version 10. Android’s documentation describes what DSU does: it “Creates a new dynamic partition. Loads the downloaded GSI onto the new partition. Boots the GSI as a guest OS on the device.” A GSI, or Generic System Image, is a build of Android meant to run on many phones. Your own system and data stay where they are, and rebooting brings you back to them.

Android’s own way to start DSU is an adb command or a developer option. DSU Sideloader, by a developer called VegaBobo, wraps that in an app: you pick an image file, it prepares it and starts the installation. The project calls itself “basically a ‘front-end’ for Android’s DSU feature”. Its last release, 2.03, came out in April 2023, and more than a hundred issues are open.

What you need

• Android 10 or later, on a phone whose maker has enabled DSU. Android says availability is up to the manufacturer and that Google has enabled it on Pixel 3 and newer.
• An unlocked bootloader, for most images. On a locked phone, DSU only boots system images signed by Google, by the phone maker or with a key the maker has set the phone to trust; the README puts it as “most GSIs requires unlocked bootloader”. The app itself is stricter: before you start, it warns that you “MUST unlock bootloader”, “MUST have some way to restore device stock firmware”, and that a full backup is “RECOMMENDED”.
• Dynamic partitions, which the app checks for.
• A GSI that matches your phone: its processor architecture, and according to Android, a security patch level newer than your current system’s, because DSU refuses to roll back.
• Space. Android recommends keeping at least 10 GB free, and the app warns below 40% free on the data partition. It also needs a folder for temporary files, where compressed images are unpacked.

How it starts the installation

The app picks the strongest mode available, from the code of version 2.03:

It accepts .img, .gz, .xz and .zip files; ZIP files must be DSU packages, the multi-partition format Android 11 introduced. Before starting, it turns on the system flag that enables DSU, the same setprop command Android’s documentation gives.

Getting back

After the installation, Android’s own DSU notification offers to restart into the GSI. A normal cold reboot then returns you to your own system, unless sticky mode is on, which keeps booting the GSI until you turn it off with adb shell gsi_tool disable. Discard in the notification, or in the app with root, removes the GSI. The developer says that removes all of the installation’s files and partitions, without a factory reset.

What can go wrong

The README calls DSU “very safe”, since no read-only partition is modified. Reports in the issue tracker are less reassuring, and we couldn’t check them:

• A Pixel 6a showed “Your device is corrupt” after a DSU attempt; the developer suggested restoring the firmware with Android Flash Tool.
• Sticky mode turning on by itself, so that rebooting didn’t return to the original system.
• The original system not booting after a modified GSI, until the user formatted data.
• On Samsung phones, Knox likely trips, though the developer wrote that they couldn’t test it.

Two root-mode details to know: on SELinux errors, the app offers Retry with permissive, which switches SELinux to permissive, something its own text calls “not recommended, weakens your device security”. And when it shows installation progress, it clears the system log first, with logcat -c.

What goes online

Only an update check, and only when you tap it in About. The app reads a small file from the project’s GitHub repository and, if you tap Download, fetches the APK from GitHub and opens Android’s installer. The updater only appears in builds signed with the developer’s key, which this one is. The update file currently lists the same version, so it reports that you are up to date. There are no analytics or crash-reporting libraries.

About this file

• This is the developer’s own build of version 2.03, byte for byte the app-release.apk on the project’s GitHub release. F-Droid distributes the same signed file, so this copy, F-Droid’s and GitHub’s update one another.
• The 5.1 MB file runs on Android 10 and later and declares 9 permissions. Several of them, such as installing a dynamic system, unmounting the SD card and force-stopping apps, are system permissions that Android only grants when the app is installed as a system app through the project’s Magisk module; in a normal install they do nothing. Internet access and installing apps are for the updater.
• DSU Sideloader is licensed under the Apache-2.0. The module’s custom system binaries live in the same repository but aren’t in this APK.
• The screenshots, from the project, show version 2.01; the bootloader warning added in 2.03 isn’t in them.

Shizuku API. Uses the Shizuku API, so it can do ADB-level work without root once Shizuku is running. (rikka.shizuku.Shizuku$$ExternalSyntheticLambda0)

libsu (root shell). Bundles libsu, a library for running commands in a root shell. (com.topjohnwu.superuser.CallbackList$$ExternalSyntheticLambda0)