A must use (mu) plugin is like a normal WordPress plugin except you can’t deactivate it.
It runs as soon as you upload it using a FTP client (Filezilla, Transmit, Cyberduck etc.).
To deactivate it, just delete its directory from wp-content/mu-plugins.
Several hooks (including SEOPress ones) must be loaded via a mu-plugin.
It’s also a good alternative if you don’t have a functions.php file.
To create a must use plugin, go to wp-content/mu-plugins directory.
If this folder is not available, add it.
Then create a new file called “seopress-mu.php” (the name doesn’t matter).
Paste this snippet to seopress-mu.php:
And add your own custom code (like actions and filters) to your new mu-plugin.
Test carefully your code! Remember, a mu-plugin is always activated.
You will see your mu-plugin from your WordPress admin, Plugins list, Mu-plugins tab.