Thank you for your support.
I believe the port is OK, I run dmesg | grep -i tty I get that the Arduino is connected to port /dev/ttyACM2 (matches what is shown in th IDE).
Actually, the whole thing was working perfectly until I did something that I guess is a big NO-NO:
connected the 9V battery directly to Aduino (5v and GND pins) :roll_eyes:
The 13th pin LED blinks (if I plug an external LED, also blinks) and when I try to upload a sketch, both RX and TX blink as well.
So, by elimination I could say that the problem could be concentrated in a specific component: the microcontroller.
I already ordered a new chip and a AVR programmer, but still your opinion is very important to me.