一般Virtualbox安裝CentOS安裝完成後默認是800x600的分辨率。
安裝Guest additions。安裝完成後，分辨率可以修改為1024x768，還有一些更高的分辨率，但是沒有1366x768。
修改/etc/X11/xorg.config
安裝完Guest additions後，文件默認內容為(或者類似)
# VirtualBox generated configuration file
# based on /etc/X11/xorg.conf.
Section "Monitor"
Identifier "Monitor[0]"
ModelName "VirtualBox Virtual Output"
VendorName "Oracle Corporation"
EndSection
Section "Device"
BoardName "VirtualBox Graphics"
Driver "vboxvideo"
Identifier "Device[0]"
VendorName "Oracle Corporation"
EndSection
Section "Screen"
SubSection "Display"
Depth 24
EndSubSection
Device "Device[0]"
Identifier "Screen[0]"
修改Section "Screen"，添加字段Modes "800x600" "1366x768"
Section "Screen"
SubSection "Display"
Depth 24
Modes "800x600" "1366x768"
EndSubSection
Device "Device[0]"
Identifier "Screen[0]"
注意：Modes要添加在SubSection之間，而且不能只添加1366x768，要同時添加800x600。
