java.lang.IllegalArgumentException - ubuntu 16.04

Hello all,

I try to make a home server with ubooquity. I installed Java and downloaded ubooquity.jar (v2.1.1) both on a raspberry pi 2 running raspbian and on a mini pc running ubuntu (atom d525 + 4go ram). On both computer I have the same error, which I copy below. May you help me ?

Command line arguments error: java.lang.IllegalArgumentException: The provided execution directory does not exist or is not writable
Launch Ubooquity with the "--help" option to display available commands
Ubooquity has stopped