So I moved some files to an USB stick and deleted them afterwards. I did this multiple times and I expected my free space to be around 3GB. However it says that I only have a couple hundred MBs of free space.
Hence I used
du -h and
xdiskusage to check what's taking up the space.
du -h doesn't show anything and the consumed space is 3GB below the USB -stick capacity.
xdiskusage shows me a 3GB block called "(permission denied)" which seems to be the cause of the missing space.
(I also ran
sudo lsof | grep deleted to see if anything has deleted files opened.)
How do I free this space?
I'm using Debian 9 with KDE and the dolphin file manager.