To perform chart generation, Financial Reporting requires access to a graphics display device, either real or virtual. Oracle recommends that you use an X virtual frame buffer (Xvfb) instead of a hardware graphics display device, because Xvfb performs all operations in memory and does not require that screens or input devices be attached to the machine. For details about enabling Xvfb, see Enabling an X Virtual Frame Buffer for Financial Reporting and Production Reporting.
You must also set the DISPLAY variable for Production Reporting to generate charts.