It works ! Thank you again.

The gqrx GUI doesn't fit into the screen and it seems that the cpu load is to heavy to work seamlessly but wtf it works on N900 !

I also tried multimon-ng, there is no error, I think it works but I have no possibility to test a signal today.

Even if rtl_fm is the only continuous part I'm very lucky

My dongle is a "Terratec ran T-Stick+", not mentioned at the most manuals, but it works with rtl-sdr on N900, raspberry PI, Debian, Win sdr#, ... bought at "Conrad" store (20€, there are cheaper dongles but if you can't wait it's ok)