Mu-plugins (also known as ‘must use’ plugins) are the plugins located in the “mu-plugins” folder. These are activated by default, affecting all sites on a WordPress Multisite installation.
- 95 % of WPMU DEV plugins are now designed to be installed in the /wp-content/plugins/ folder on your site. A few, however, like multi-DB, domain mapping, multi-domains, additional tags need to be installed in the /wp-content/mu-plugins/ folder
- Always read carefully all installation instructions for the plugin because some plugins involve uploading PHP files and folders to a range of different locations.
Setting up your mu-plugins folder
Before you can install mu-plugins on your WordPress Multisite installation you need to create a mu-plugins folder as follows:
1. Create your mu-plugins folder in wp-content using FileZilla by right clicking and selecting Create directory.
2. Add the directory name mu-plugins and click OK.

3. Right click on your mu-plugins directory and select file permissions.
4. Set the file permission to 755 and click OK.

Installing mu-plugins
Alternatively, refer to our video tutorial on installing mu-plugins using FTP.
If you are using Multi-DB:
- You need to add the global table lines to db-config.php BEFORE installing the plugin or running the sql.txt
- The plugin’s install file will specify which lines to add to your db-config.php if using multi-db.
Install the mu-plugin as follows:
1. Download the plugin
2. Unzip the file to extract all files into a folder on your hard drive
3. Read all installation instructions for the plugin carefully – some plugins involve uploading PHP files and folders to a range of different locations.
- Make sure you read these instructions carefully
- Many mu-plugins require additional steps to install other than those explained below
- If you don’t follow these instructions correctly the plugin won’t work and may cause problems on your installation
About WPMU DEV plugins installation instructions
- WPMU DEV plugins don’t include readme or install files. You need to refer to the install page where you downloaded the plugin.
- The installation page contains detailed step-by-step instructions for installing as well as instructions on how to use the plugin.
- For example, this is the installation page for multi-domains.

4. Launch FileZilla
5. Enter your domain name, your username and password.
6. Click Quickconnect
See Next: WPMU DEV Plugins Separated into Categories to Help Make Selecting Your Next Plugin Easier
