I have a pb with twisted.internet.utils.getProcessOutput (i never get the output :() here is an exemple : class PGAT_deftest(GAT_page): template="""<html><body><span view="Viewtest"></span></body></html>""" def wvfactory_Viewtest(self, request, node, model): return MyDeferredWidget(model) def render(self, request): request.write('<html><body><h1>DEFTEST</h1>'+ time.asctime()+'<br >') print "Emerge !" d = getProcessOutput("ps") d.setTimeout(5,self.renderProcessOutput, request) d.addCallback(self.renderProcessOutput, request) d.addErrback(self.renderError, request) d.addCallback(self.finishPage, request) return NOT_DONE_YET def renderProcessOutput(self, output, request): request.write(output) def renderError(self, failure, request): request.write('it broke! (error : "'+failure.getErrorMessage()+'")') def finishPage(self, _, request): request.write('</body></html>') request.finish() def montest(): time.sleep(5) return "Ca marche !" If I create a bash script with : --- sleep(5) echo "Hello world" --- the twisted code above works great. But If I use a system program like "ps" or "emerge" , the callback is never called :( (btw : getProcessOutput ("date") works)