adb shell su works but adb root does not

Question

I rooted my unlocked Galaxy S3 (SGH-T999)

Now, I\'m trying to run adb root from Windows Command Prompt, however, I\'m getting adbd cannot

Answer 1

adbd has a compilation flag/option to enable root access: ALLOW_ADBD_ROOT=1.

Up to Android 9: If adbd on your device is compiled without that flag, it will always drop privileges when starting up and thus "adb root" will not help at all. I had to patch the calls to setuid(), setgid(), setgroups() and the capability drops out of the binary myself to get a permanently rooted adbd on my ebook reader.

With Android 10 this changed; when the phone/tablet is unlocked (ro.boot.verifiedbootstate == "orange"), then adb root mode is possible in any case.