I made this app as a solution to the following question that I asked on Android Enthusiasists StackExchange:
Despite repeated efforts to explain them, some family members keep turning off the private DNS setting in Android, which leads to the invasion of their phones by ads, trackers and malware. So, I want to lock down the private DNS setting so it can't be changed or turned off, and I need to do it without using root or third-party apps. The problem with third-party apps is that they will see the app on the launcher or in Settings > App and just uninstall it to bypass the block. And if I set the DNS on the WiFi router itself, they will refuse to use the WiFi and use cellular network instead.
I'm desperate, is there any solution?
and also to this question asked by another user.
This app is fully FLOSS, and works without root. It needs only one-time ADB access for the first-time setup.
First, instead of actually locking the Private DNS setting (which would require modification of the Settings app, which in turn requires root), this app runs every minute and sets the Private DNS to a hostname you specify! So, even if Private DNS has been turned off, it will be turned on again by this app and set to the desired hostname, just a minute later. The app itself does NOT run in the background to do this; It uses AlarmManager to schedule the starting of a BroadcastReceiver every minute, which means the app will continue to function even if it has been killed! This also makes the app relatively friendly towards battery life and RAM usage.
Second, the app is disguised under a convincing name ("Android System Services") and has no launcher icon, which makes it less likely to become a suspect for getting uninstalled. The app itself is also only a few hundred KBs in size when installed, just like most other system apps.
This app is CLI-only. To set it up, first ensure that you have enabled USB Debugging in Developer options and authorized your PC on the phone. Now run this command:
adb shell 'pm grant com.android.system.services android.permission.WRITE_SECURE_SETTINGS && am broadcast -n com.android.system.services/.IReceiver -e PrivateDnsHostname "<private DNS hostname>"'
Replace <private DNS hostname> with the desired hostname. For example:
adb shell 'pm grant com.android.system.services android.permission.WRITE_SECURE_SETTINGS && am broadcast -n com.android.system.services/.IReceiver -e PrivateDnsHostname "dns.adguard.com"'
The app will start working, and after this, you can also disable Developer options.
The app also starts automatically at boot.