My app must receive parameters from command line as well run another instance when it is invoke without any parameters. QtSingleApplication is new to me but after quick look at it's documentation I think it is not best solution for me. I create custom Application class with local socket and with signal showMainWindow() which I emit to main window raiseWindow() after obtaining file name from socket. I do exactly the same as it is in demo Browser from Qt demos. And in true I have the same behaviour (this is bad).