Browser blank page / white page with php script (WordPress, etc.)

I recently had a completely white / blank browser page when I tried to reset my WordPress password. It was from a local WordPress installation on my Debian 8 Jessie server. I was resetting my password for the admin login. It turned out that there was a problem with my php.ini settings. I had to add the following paths to the open_basedir variable:

open_basedir = /usr/share/php:/usr/share/php5

When resetting the WordPress password, WordPress includes some php files to send a reset email in wp-includes/pluggable.php:

require_once ABSPATH . WPINC . '/class-phpmailer.php';
require_once ABSPATH . WPINC . '/class-smtp.php';

The problem is that with the standard wordpress package on Debian 8 Jessie, class-phpmailer.php and class-smtp.php are symbolic links to /usr/share/php/... . If this path is not included in open_basedir, the php script just terminates without sending any error messages. I couldn't find anything in the apache logs either. The browser showed a blank page.

This might also be a problem with other php web applications. So if you experience a similar situation (no output of php script, blank page) you might want to check the open_basedir variable in you php.ini and make sure that all required / included php files and symbolic links are part of it.

If you have any ideas how to find out if a php script is trying to include a file outside of open_basedir, please leave a comment.