To build and install Discern on Debian/Ubuntu, several dependencies are required, including xmkmf (in package xutils-dev), and XT and Xaw development packages. Do:
$ sudo apt-get install xutils-dev libxt-dev libxaw7-dev
To install, do:
$ xmkmf
$ make
$ make install
Please see [this post at PatternsInTheVoid] 1 for admittedly outdated information.