Android development RecoverySystem.installPackage() cannot write to /cache/recovery/command permission denied

Question

I have been asked to write a small simple app for an Android-based product. The device comes with two Android system images with different features. The app I\'m writing is

Answer 1

System apps (apps with shared user ID set to android.uid.system) cannot install system updates on Android 5 and newer - it's forbidden by a SELinux policy. To be specific writing to /cache is forbidden for system apps. In other words:

• /cache is owned by system user so your app running under system UID can write to it. But only if SELinux is disabled/permissive.
• If you have android.permission.ACCESS_CACHE_FILESYSTEM platform signature permission, you can write to /cache.

You'll need to remove the shared user ID. You still have to sign the app with platform signature and ensure you have the following permissions:

• android.permission.REBOOT
• android.permission.ACCESS_CACHE_FILESYSTEM - to write to /cache
• android.permission.RECOVERY - required on API 21 to reboot to recovery

This will work on Kitkat and Lollipop+ alike.