Whenever you’re upgrading the software packages on your VirtualBox machine, managed by Vagrant, you risk VirtualBox Guest Additions render unusable and thus your shared folders don’t work anymore. This usually happens whenever a kernel upgrade is being done which requires the VirtualBox drivers to be recompiled.
Thanks to a Vagrant plugin called vbguest you can now safely upgrade your software packages. If you’ve got this plugin installed every time you run vagrant up it’ll check the installed version of VirtualBox Guest Additions and updates it accordingly.
To install the plugin run the following command from your shell:
$ vagrant plugin install vagrant-vbguest