由于之前重复的安装卸载Unity桌面，今天遇到了在设置虚拟机分辨率的时候，遇到了Unknown Display问题。
参考网上内容，使用 xrandr调节分辨率。
xrandr只能在虚拟机本地终端执行，不能使用ssh远程操作。
1.输入xrandr查看可设置的分辨率取值*为当前屏幕分辨率取值
dream361@ubuntu16:~$ xrandr
Screen 0: minimum 1 x 1, current 1360 x 768, maximum 16384 x 16384
Virtual1 connected primary 1360x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
800x600 60.00 + 60.32
2560x1600 59.99
1920x1440 60.00
1856x1392 60.00
1792x1344 60.00
1920x1200 59.88
1600x1200 60.00
1680x1050 59.95
1400x1050 59.98
1280x1024 60.02
1440x900 59.89
1280x960 60.00
1360x768 60.02*
1280x800 59.81
1152x864 75.00
1280x768 59.87
1024x768 60.00
640x480 59.94
Virtual2 disconnected (normal left inverted right x axis y axis)
Virtual3 disconnected (normal left inverted right x axis y axis)
Virtual4 disconnected (normal left inverted right x axis y axis)
Virtual5 disconnected (normal left inverted right x axis y axis)
Virtual6 disconnected (normal left inverted right x axis y axis)
Virtual7 disconnected (normal left inverted right x axis y axis)
Virtual8 disconnected (normal left inverted right x axis y axis)
2.临时设置分辨率
dream361@ubuntu16:~$ xrandr -s 1280x768_59.81
3.永久设置分辨率，参数output的值，Virtual1 根据第一步输出信息得到
dream361@ubuntu16:~$ xrandr --output Virtual1 --mode 1360x768
负责任的讲一下，上面的永久设置在重启之后会失效！