Running Linux apps on Android without rooting your phone

Building Your Own UserLAnd

Why compile UserLAnd yourself? First, compiling UserLAnd lets you work around the Android 10 storage policy. Second, you might have new ideas and want to collaborate on the project. If the motive is to disable the storage restrictions, you should definitely be aware of the risk of removing what is in principle a sensible security barrier.

You can download the source code of UserLAnd directly from GitHub [2] and then open it with Android Studio 4.x [8]. If you want to bypass the new storage policy, you can compile UserLAnd with an older Android SDK, such as version 28, which predates the restrictions. To install version 28, you have to edit the app\gradle.build file in three places (Listing 8).

Listing 8

Changes to app\gradle.build

compileSdkVersion 28
targetSdkVersion 28
versionName "2.7.2-Android9"

As usual, you'll need to set your own device as a developer device and install the software APK from the PC with adb [9] or via the file manager in the device. Annoyingly, you have to uninstall the official UserLAnd version beforehand (due to the different or missing signature) and thus lose all data the Linux system set up.

Limits and Problems

Probably the most annoying weakness of the UserLAnd solution for Linux on Android is the limited number of open windows (three to six), which can even decrease during the session. UserLAnd then reports

Maximum number of clients reached. Failed to open display.

What is also very annoying is that the connection to the VNC server occasionally breaks down. Then you lose all your unsaved data because you can't connect to the session anymore.

Some VNC viewers had trouble transferring keystrokes for non-English character sets. AndroidVNC does not have the problem, but it is no longer maintained and has many other shortcomings. RealVNC's PC viewer, on the other hand, transfers the key combinations correctly.

Wireless mice often react clumsily. This seems to be a hardware problem that cannot be solved via the energy-saving settings. It is also annoying that you cannot shut down a Linux session and have to stop it in Android instead.

On the positive side, the filesystem can be exported and used as a backup – very handy for transfers to other devices, but keep in mind that backing up the filesystem can take some time.

Conclusions

The age of full-fledged pocket-sized computers has arrived. Once a few teething problems have been solved, these computers can be used at home without restrictions. Smartphones can already handle many basic applications, but you still need modern desktop computers or laptops for special tasks and 3D games with high performance and resource requirements. I also own a smartwatch with a dual-core CPU and 4GB RAM, and I am already wondering whether I'll be able to get a Linux distribution running on it.

The Author

Dirk Ambras works at Airbus as an IT expert. He used to work for Siemens as an operating system developer for cell phones in the areas of graphics, games, and Java. The fun of working with embedded devices is something he has never lost.

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