Bingo ! i get error messages "Execution of JACK server failed", and several "cannot connect to named pipe after wait". I tried to start pd with --disable-jack (as found here https://github.com/pure-data/pure-data/issues/25 ) but pd doesn't start.
This is a flag to pass to the ./configure program when compiling Pd from its source code. It is not a flag to start Pd with.