The DUP System

All current components of the DUP System are released under the GNU Public License (GPL).

Note that this license only applies to the DUP code and the filters shipped with DUP. It is legal for you to write your own applications with the DUP System and to use DUP filters as part of the resulting application. Since all of the DUP filters as well as dup and dupd would be run as seperate processes, it is my (and, as far as I know, the FSF's) interpretation of the GPL that DUP and the DUP filters being GPLed imposes no requirements on the licenses for your application or the other filters it may be using. However, if you modify or distribute the C/C++ code of the DUP implementation itself, you will have to redistribute those modifications under the GPL.