sudo not installed, su not enabled

lobman

hi, i managed to compile the Ubuntu 16.04 amd64 firmware from firefly instructions (after trapping a bunch of gcc compile warnings in a number of MakeFiles), burned it onto an sd, the firefly booted into the terminal, and i logged in with my username and password. so far so good. when i try to install xfce i find that sudo is not found and there is no root password to drop into su. would someone please enlighten me how to obtain permission to install? i am stuck and see no easy way forward. any advice greatly appreciated.

leung先森

sudo -s   ?
username and passwd were 'firefly'