Linux版本的VirtualBox下载：http://www.virtualbox.org/wiki/Linux_Downloads。请下载对应的版本。
RedHat、RHEL:rpm -i vh *.rpm
Ubuntu安装：sudo dpkg -i *.deb
如果虚拟的是linux系统，那么如何安装GuestAdditions
在linux系统中选择安装增强功能，然后会自动关在GuestAdditions的ISO文件，有如下的窗口打开，复制里面的VBoxLinuxAdditions.run文件（可能位于/media/VBOXADDITIONS_version），然后执行。(这里以CentOS 为例)
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执行安装就可以了
# bash VBoxLinuxAdditions.run
Verifying archive integrity... All good.
Uncompressing VirtualBox 1.6.4 Guest Additions for Linux installation.............................................................................................................................................................................
VirtualBox 1.6.4 Guest Additions installation
Building the VirtualBox Guest Additions kernel module...
Building the shared folder support kernel module...
Installing the VirtualBox Guest Additions...
Successfully installed the VirtualBox Guest Additions.
You must restart your guest system in order to complete the installation.
安装后需要重新启动虚拟机。。。。
Linux or Solaris/OpenSolaris虚拟机的系统必须有X.org Server 1.3或以上版本才可以有无缝模式seamless Mode效果。
文件夹共享：# mount -t vboxsf [-o OPTIONS] sharename mountpoint
例如:#mount -t vboxsf download /mnt/box，前提是挂载点必须存在
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虚拟linux系统的显示及分辨率
安装完增强功能后，会简单的修改xorg.conf文件就可以了，modes设置你需要的分辨率
Section "Screen"
Identifier "Screen0"
Device "Videocard0"
Monitor "Monitor0"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
Modes "2048x800" "1024x640" "800x600" "640x480"
EndSubSection
EndSection