Debugging white screens (including empty ACP Plugins page listings)

[Laird]

Sometimes, MyBB outputs a white (blank) screen - and for this post's purposes this includes a truncated or empty list of plugins on the ACP Plugins page - without outputting any error messages either to the log file or via email, despite having been configured to do one or the other via the error-related settings under Server and Optimization Options.

This post is intended to explain how to determine the error message behind any given white (blank) screen in those scenarios in which MyBB doesn't otherwise output it, so that further more specific help can then be provided.

In a nutshell, the solution is to turn your php.ini display_errors setting on.

How to do this depends on your hosting environment. Here are some possibilities:

1. Some hosting control panels such as cPanel provide a means to edit php.ini settings via their web interface. If so, dig around in there or contact your hosting provider to find out how to do this.
   
2. Directly edit your effective php.ini file. The easiest way to find out the location of your effective php.ini file is to create in your web root a file phpinfo.php or something like that with these contents:
   

   <php
   phpinfo();
   

   and to then browse to that file and note in the output page the file location beside "Loaded Configuration File". That's the file you need to edit. If there is a line in it beginning with display_errors = then edit it to read as follows; otherwise add the line which follows:
   

   display_errors = On

3. Sometimes, you can turn on display_errors via your site's .htaccess file if supported by your web server. In that case, add this to your .htaccess:
   

   php_flag display_errors on
   

Note 1: After the error is resolved, if yours is a production board, then you should for safety turn display_errors back off, and delete any phpinfo.php file created in step #2 above.

Note 2: If the white (blank) screen you're experiencing is in the ACP's plugins module, and is only partial - with only the contents pane being empty, as in this "in the wild" example - then this might be because you have neglected to install a plugin's dependencies. For example, the MyAlerts plugin depends on Plugins.Core and PluginLibrary, and failing to install both dependencies can result in a blank plugins module screen.

If anybody has any feedback on this little how-to, then please share it, and I'll update this post if appropriate.