Here you can find who and how use setfsuid(...):http://www.google.com/codesearch?hl=ru&sa=N&q=%5B%5E_%5Dsetfsuid%5B%5C+%5Ct%5D*%5C(%5Ba-z_%5D%2B+file:%5C.%5Bch%5D%5Bcpx%5D*%24