dear sir, i use ubuntu VM as server. recently i downloaded a lot files, say a total of 5 GB, so the VM size increased. Before the download, the ubuntu VM size is 15 GB. After download 5 GB files, the VM size is 20 GB. But when delete all the downloaded 5 GB files (rm file1 file2 file3 ......), the VM size is still very closed to 20 GB (it should be closed to 15 GB). Even clean the files under /lost+found, /tmp, /Trash directories, but the VM size is still very closed to 20 GB. This is very strange. Why those downloaded files can't be completely removed and how to do this?