1. Unknown display in Ubuntu 14.04
input command under terminal :
1. xrandr 2. sudo cvt 1280 1024 60
3. xrandr --newmode "1280x1024_60.00" 109.00 1280 1368 1496 1712 1024 1027 1034 1063 -hsync +vsync
4. xrandr 5.xrandr --addmode VBOX0 "1280x1024_60.00"
6.xrandr -s 1280x1024_60.00 (ok!)
原文：https://www.cnblogs.com/sancai16888/p/9650853.html