This commit catches the Errno::EPERM raised by the operating system if the machine folder is inaccessible and displays it as a more friendly error message. This can be an issue on macOS Catalina if virtual machine files are kept in a special directory (Documents/Downloads/Desktop) that Vagrant's embedded Ruby is not allowed to access.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.