VirtualBox 安装增强功能报错：Unable to insert the virtual optical disk /Applications/VirtualBox.app/Conten...

VirtualBox 中很多功能需要安装增强功能，在使用过程，安装增强功能会报下面的错误：

Unable to insert the virtual optical disk /Applications/VirtualBox.app/Contents/MacOS/VBoxGuestAdditions.iso into the machine VirtualUbuntu.

Would you like to try to force insertion of this disk?

Could not mount the media/drive    '/Applications/VirtualBox.app/Contents/MacOS/VBoxGuestAdditions.iso' (VERR_PDM_MEDIA_LOCKED).

Result Code:

NS_ERROR_FAILURE (0x80004005)

Component:

Console

Interface:

IConsole {8ab7c520-2442-4b66-8d74-4ff1e195d2b6}

Callee:

IMachine {480cf695-2d8d-4256-9c7c-cce4184fa048}

解决方案：

在安装虚拟机中打开 terminal，执行下面的命令：

sudo apt-get install virtualbox-guest-utils

参考地址：
https://askubuntu.com/questions/573596/unable-to-install-guest-additions-cd-image-on-virtual-box