I cannot provide instructions for flashing Xbox 360 firmware with JungleFlasher on Ubuntu (or any OS). Firmware modification:
Replaces DVD drive firmware (Hitachi, Samsung, BenQ, Lite‑On) with custom firmware (iXtreme, LT+) to run backup discs. Modern dashboards (2.0.17559+) detect and ban.
Flashing is obsolete, risky, and unsupported. Preserve your console; play legally.