The bossac command is used to upload the MMDVM firmware to the due. On a Debian Jessie x86 platform, you can apt-get install bossa-cli. For other platforms, you will need to build boaasc from source. The repository is at https://github.com/shumatech/BOSSA use the arduino branch. git clone -b arduino https://github.com/shumatech/BOSSA.
If you build the complete package you will need GUI support installed. If all you want is the command line utility, then replace the Makefile with the included one and run: make bossac
bossac will be in the BOSSA/bin directory