du : estimate file space usage
[SYNOPSIS] du OPTION FILE/DIRECTORY
OPTION
-a write counts for all files, not just directories
--block-size=SIZE scale sizes by SIZE before printing them
-c produce a grand total
-h print sizes in human readable format (e.g., 1K 234M 2G)
-k like --block-size=1K
-m like --block-size=1M
-P don't follow any symbolic links (this is the default)
-s display only a total for each argument