man(1) Manual page archive

     du  -  summarize disk usage

     du [ -s ] [ -a ] [ name ... ]

     Du gives the number of blocks contained in all files and
     (recursively) directories within each specified directory or
     file name.  If name is missing, `.'  is used.

     The optional argument -s causes only the grand total to be
     given.  The optional argument -a causes an entry to be gen-
     erated for each file.  Absence of either causes an entry to
     be generated for each directory only.

     A file which has two links to it is only counted once.

     Non-directories given as arguments (not under -a option) are
     not listed.

     Removable file systems do not work correctly since i-numbers
     may be repeated while the corresponding files are distinct.
     Du should maintain an i-number list per root directory