du [options] [directories]
Print disk usage; i.e., the number of 512-byte blocks used
Print disk usage; i.e., the number of kilobytes used
by each named directory and its subdirectories (default is current directory).
Print usage for all files, not just subdirectories.
Print "cannot open" message if a file or directory is inaccessible.
Print only the grand total for each named directory.