Vagrant: Failed to mount folders in Linux guest. This is usually because the "vboxsf" file system is not available.

This is an issue of older version of VirtualBox. Download the latest virtual box from :
Virtual box Download site

You may need to do the following also if not resolved after upgrading to latest version:

$ vagrant plugin install vagrant-vbguest

More tips to solve the problems:

https://github.com/mitchellh/vagrant/issues/3341

https://www.virtualbox.org/manual/ch04.html#idp54932560