I have a rooted Android Phone and a native service which detects if the system partition is mounted read-write or read-only.
If I run the mount command in the user shell, the partition is mounted read-only.
mount | grep /system
I can open a different shell, login as root and run the command
mount -o remount,rw /system
In the root shell, the system is mounted read-write, but in the previous opened user shell, the system partition is still mounted as read-only. Even if I switch back in the rooted shell with Ctrl+D to the normal user shell, the system partition is mounted read-only. It is only read-writeable in the root shell.
So it is not possible to detect as non root, if the partition was remounted in a different context. Why is that? As it is of my knowledge, in Linux mount points are handled globally.
Update: Android 5.0.2, Samsung SM-A300FU and SM-A300M