Unable to mount filesystem as read-write in recovery mode
Solution 1:
If I am not wrong, the filesystem is mounted read-only by default in Recovery mode. To mount it as read-write, go the recovery mode and choose root. Now type the following command:
mount -o rw,remount /
Note the spaces, you'll get an error if you ignore the spaces, or add extra ones too. And then you can copy as you tried earlier.