FlRig 1.3.27-1 Deb Install on LinuxMint 18
You can compile from source but to save time if you want to have the latest (as of the date of this post Nov 22 2016) flrig I have compiled up a DEB file that is built for linuxmint 18, but should also work with mint 17 as well as any other distro that uses that same ubuntu base.
First you need to install the dependencies
Now Download the flrig_1.3.27-1_amd64.deb file Open up a console, cd into that download folder and run the following command to install it.
You should now have a working version of FlRig that will work with the Yaesu FT-991.