V3/man/man1/du.1

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NAME		du  --  summarize disk usage
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SYNOPSIS	du__  [ -s__ ] [ -a__ ] [ name ... ]
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DESCRIPTION	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 generated
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.
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FILES		.
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SEE ALSO	--
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DIAGNOSTICS	--
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BUGS		Non-directories
given as arguments (not under -a option) are not listed.
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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
encountered.