解决方法：
sudo apt-get install --reinstall linux-image-$(uname -r)
参考：http://askubuntu.com/questions/596998/unable-to-install-guest-additions-unknown-filesystem-type-iso9660
VirtualBox安装增强工具时：Unable to install guest additions: unknown filesystem type 'iso9660'
原文：http://www.cnblogs.com/hubery/p/4747920.html
