sudo piaware-config rtlsdr-gain 30 (replace 30 by the gain value you want to set)
sudo piaware-config -show rtlsdr-gain
sudo systemctrl restart dump1090-fa (must restart dump1090-fa to implement the new gain value)
sudo systemctrl status dump1090-fa -l
You got it wrong.
If it was Piaware 3.5 SD Card image, it will be “pi@piaware” , not "pi@raspberrypi"
Your install is Raspbian Jessie image with Piaware and dump1090-fa add-on
In this case sudo piaware-config command will be saved in piaware.conf file, but will NOT be transferred to dump1090-fa settings.
You have to edit file “dump1090-fa” and change gain setting.
(1) Give following command to open file dump1090-fa in editor nano