我正在尝试运行Vagrant，但在执行
如何帮助他检测VirtualBox？
vagrant up命令后出现错误：No usable default provider could be found for your system.
Vagrant relies on interactions with 3rd party systems, known as
"providers", to provide Vagrant with resources to run development
environments. Examples are VirtualBox, VMware, Hyper-V.
The easiest solution to this message is to install VirtualBox, which
is available for free on all major platforms.
If you believe you already have a provider available, make sure it
is properly installed and configured. You can see more details about
why a particular provider isn't working by forcing usage with
`vagrant up --provider=PROVIDER`, which should give you a more specific
error message for that particular provider.
我之前安装了VirtualBox版本4.3.26 r989888和Linux Ubuntu（64位）。
之后执行以下命令：
vagrant box add precise32 http://files.vagrantup.com/precise32.box
==> box: 正在为提供程序添加'precise32'(v0)：
box: 正在下载：http://files.vagrantup.com/precise32.box
box: 进度：100%（速率：1425k/s，剩余时间：--:--:--）
==> box: 成功为'virtualbox'添加'precise32'(v0)！
当我执行以下命令时：
vagrant box list
lucid32 (virtualbox, 0)
precise32 (virtualbox, 0)
"Provider"存在什么问题
vagrant package --base vagrant-ubuntu64
Vagrant could not detect VirtualBox! Make sure VirtualBox is properly installed.
Vagrant uses the `VBoxManage` binary that ships with VirtualBox, and requires
this to be available on the PATH. If VirtualBox is installed, please find the
`VBoxManage` binary and add it to the PATH environmental variable.
如何帮助他检测VirtualBox？
