mu-plugins aren't loading

Question

I've looked at other posts regarding mu-plugins but I don't understand yet. Here's the situation: My site is hosted by a service that automatically sets up 2 caching plugins. Cloudflare and OP Cache. They were originally installed in the mu-plugins folder. I'm not sure what happened, as there are multiple people working on this site, but they all disappeared.

I reinstalled them but can't activate them. I got the error

Fatal error: Cannot redeclare class OPcache_dashboard in oursite/www/wp-content/plugins/opcache/opcache.php on line 28

So I guess when I reinstalled them, it put them in the normal plugins folder. If I delete the mu-plugins version, I can then activate it. However, what I'd like to do is keep them in the mu-plugins folder and activate them from there, but they don't appear unless they're in the normal plugins folder.

Any thoughts?

Thanks in advance!

Answer 1

The reason plugins in the mu-plugins folder can't be activated in the plugins page is because that's not how mu-plugins works. The mu stands for must use.

Improtant things to know:

• mu-plugins load before plugins
• WP loads PHP files in the mu-plugins folder
  • it does not search subfolders
  • it does not look for plugin headers
• PHP files in the mu-plugins folder have no activation status, they are always loaded.
  • this is true for all sites in a multisite, there is no conditional loading.

So code in the mu-plugins folder will never have an activate/deactivate link. You can never put code in both mu-plugins and plugins. You also can't just put a plugin in mu-plugins, it needs a PHP file that includes the plugins main file to work.

mu-plugins is a folder of PHP files, where WP loads all the PHP files before it loads the plugins or themes.

Answer 2

Where that error comes from is hard to say. Obviously something needs that class, but it hasn't been included/autoloaded.

If the plugins you mentioned are designed to be in the mu plugins folder, then you should obviously place them there.

MU plugins behave a bit differently as Twerking N00b hinted at and must have an init file in the ROOT of the mu-folder (unlike normal plugins). The structure you should aim for is one init file per mu-plugin, and then the folder with the actual plugin code. The only thing the init file does, is one line with an "include", that includes the main plugin file.