solar@simple ~ $ gtf 1024 768 refresh -x

  # 1024x768 @ 0.00 Hz (GTF) hsync: nan kHz; pclk: nan MHz
  Modeline "1024x768_0.00"  nan  1024 -2147483648 -2147483648 -2147483648  768 769 772 769  -HSync +Vsync