Sometimes, you will facing the Must-Use or Drop Ins section when navigate to the WordPress Plugins list page. You can’t touch it except uninstall it by removing the plugin file from the must-use or wp-content directories, which is found in wp-content/mu-plugins by default.
Popular plugins that do belong in this folder are ones like Domain Mapping and W3 Total Cache.
Must-use plugins allow users to add features which are not present by default in the WordPress core but that are needed for users.
What’s about WordPress Must-Use Plugins
The mu-plugins directory was originally implemented by WPMU (Multi-User) to offer site admins an easy way to activate plugins by default on all blogs in the farm.
Must-use plugins (a.k.a. mu-plugins) are plugins that will always be activated by default, without you needing to do it yourself. Must User plugins are designed to have loading priority over regular plugins, it will always be executed, unless it is uninstalled.
- Always-on, no need to enable via admin and users cannot disable by accident.
- Can be enabled simply by uploading file to the mu-plugins directory, without having to log-in.
- Must-use plugins allow users to add features which are not present by default in the WordPress core but that are needed for users.
- Loaded by PHP, in alphabetical order, before normal plugins, meaning API hooks added in an mu-plugin apply to all other plugins even if they run hooked-functions in the global namespace.
- You loose the settings when change themes or plugins. By using a “Must Use” plugin, the code will always be available – no matter what network, theme, or curious guest blogger might do otherwise. It’s very useful in WordPress Multisite (Network)
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