virtualbox中安装完Ubuntu分辨率可选项很少的一种解决办法

Ubuntu中设置分辨率时发现只有640x480和1024x768两个选项，在网上搜索了一下可以使用命令xrandr去设置，可是我执行该命令却出现了

“xrandr: Failed to get size of gamma for output default” 

在网上看到了别人的解决办法，写一个配置文件然后重启就可以选择更多的分辨率了。摘取了原文一部分内容。原文地址点击打开链接

When I am trying to increase my Guest OS resolution to 1290X1080, while tried following steps mentioned HERE. Prior to that I was able to change the resolution by the above mentioned steps, but after a update to CENTOS 6.5 to 6.6, I am facing this error.Lots of people are having the same problem, but no solution I could not get my issue resolved.

I am able to get it solve to some extent by editing(creating) xorg.conf file in /etc/X11/ , the file code I am sharing below

Section "Monitor"
        Identifier   "Monitor0"
        VendorName   "Monitor Vendor"
        ModelName    "Monitor Model"
        HorizSync   28.0 - 70.0
        VertRefresh     56.0 - 75.0
EndSection


Section "Device"
        Identifier  "VMware SVGA"
        Driver      "vesa"
EndSection


Section "Screen"
        Identifier "Screen0"
        Device     "Card0"
        Monitor    "Monitor0"
        SubSection "Display"
                Viewport   0 0
                Depth     24
                Modes     "1920x1080_60.00"
        EndSubSection
EndSection