$ sudo apt-get update
$ sudo apt-get install fluid-soundfont-gm 

fluid-soundfont-gm is installed in your system.

Make ensure the fluid-soundfont-gm package were installed using the commands given below,

$ sudo dpkg-query -l | grep fluid-soundfont-gm *

You will get with fluid-soundfont-gm package name, version, architecture and description in a table

fluid-soundfont-gm package basic information: