Virtualbox安装Ubuntu9.04alpha5，安装vboxguestadditions，出现以下提示：
unknown version of the X Window System installed. Not installing
X Window System drivers.
这怎么回事，难道xorg版本太新了？

有可能是这么回事，你用的VirtualBox是什么版本的，试试最新版2.1.4。官方网站上可以下载。

是2.1.4，还是不行。

那只能祝你好运了。我在XP下用2.1.4装Ubuntu8.04，然后加载安装vboxguestadditions一点问题没有。

报错的意思好像是说 X Windows系统为未知版本，停止安装。

不知道你能不能看懂英文，我查了一下UserManual.pdf。这个文件在Viritualbox的安装目录下的doc目录里面。在其第60页有这么一段。

4.3 Linux Guest Additions
Like the Windows Guest Additions, the VirtualBox Guest Additions for Linux take the
form of a set of device drivers and system applications which may be installed in the
guest operating system.
The following Linux distributions are officially supported:
• Fedora Core 4, 5, 6, 7 and 8
• Redhat Enterprise Linux 3, 4 and 5
• SUSE and openSUSE Linux 9, 10.0, 10.1, 10.2 and 10.3
• Ubuntu 5.10, 6.06, 7.04, 7.10, 8.04 and 8.10
Other distributions may work if they are based on comparable software releases.
The version of the Linux kernel supplied by default in SUSE and openSUSE 10.2,
Ubuntu 6.10 (all versions) and Ubuntu 6.06 (server edition) contains a bug which
can cause it to crash during startup when it is run in a virtual machine. The Guest
Additions work in those distributions.
As with Windows guests, we recommend installation of the VirtualBox Guest Addi-
tions for Linux.

大意是官方只讲支持Ubuntu 5.10, 6.06, 7.04, 7.10, 8.04 和 8.10，还有所有6.10版本与6.06服务器版本会有一个bug。没说支持Ubuntu 9.04。

所以劝你换一个版本的Ubuntu吧，要么试试VMWare。如果还不行，那我就没办法了。

8.10是没问题，我估计是因为9.04还没有release，感谢你十分热心的回答！！！

這個問題在Solaris10u6也會發生，正在測試有答案在與大家分享