adb remount permission denied, but able to access super user in shell -- android

In case anyone has the same problem in the future:

$ adb shell
$ su
# mount -o rw,remount /system

Both adb remount and adb root don't work on a production build without altering ro.secure, but you can still remount /system by opening a shell, asking for root permissions and typing the mount command.

emulator -writable-system

For people using an Emulator: Another possibility is that you need to start the emulator with -writable-system. That was the only thing that worked for me when using the standard emulator packaged with android studio with a 4.1 image. Check here: https://stackoverflow.com/a/41332316/4962858

Try

adb root
adb remount

to start the adb demon as root and ensure partitions are mounted in read-write mode (the essential part is adb root). After pushing, revoke root permissions again using:

adb unroot