Measurement of size of a copied diretory with command 'du -s /path ' showed it was smaller than the original one. Checked with copying a single file - the size was different again. Why? I tried some md5sum solutions using terminal, but those were too complicated and didnt work. Then I downloaded a program tripwire but I dont know how to launch it; when I type tripwire in terminal it doesnt start. What are simple ways to verify integrity?