joystick to keyboard emulation

you can use antimicro

for Ubuntu 14.04, 15.04 and 15.10

sudo add-apt-repository ppa:ryochan7/antimicro
sudo apt-get update
sudo apt-get install antimicro

for Ubuntu 16.04

sudo add-apt-repository ppa:nilarimogard/webupd8

sudo apt-get update

sudo apt-get install antimicro

It can be used for playing showel knight

source:

http://www.webupd8.org/2014/09/gamepad-keyboardmouse-mapping-app.html