I can not delete files by pressing 'Del' key on my keyboard. I don't know why that is. The files are mounted on an external drive that auto mounts at system startup. The drive can be mounted by any user, filesystem is NTFS.
I chose NTFS so I can access the files from a windows OS if needed.
all files have 777 permissions for root:root.
I can delete the file with right-click, delete. I can also delete the file using rm without sudo.
What I cannot do is select the file and press 'Del'.
the operating system is Ubuntu 16.04.