Interactive `sed` needs write permission on the file itself. However, it may create a backup file, which leads to the fact that the directory where the file is located must be writable as well. That is a side effect because this directory does not need to be writable. This patch fixes this side effect by editing the file in `/tmp`, and replaces it right after.
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.