How to correctly use `.user.ini`-file in PHP?

In the documentation it says:

These files are processed only by the CGI/FastCGI SAPI

and

If you are using Apache, use .htaccess files for the same effect.

So if you run PHP as an Apache module, from the commandline, or using the builtin-Server, the .user.ini-files are not processed.

To find out your Server API, simply generate a PHP script with the following content and call it in your webbrowser:

<? phpinfo();

According to http://php.net/manual/en/configuration.file.per-user.php

Check user_ini.filename in your main php.ini to make sure it's not blank and it is indeed parsed. If its value is blank then PHP doesn't scan at all.

Also see the value of user_ini.cache_ttl

Please take a look at

php.net manual

Also check this question out Loading a .user.ini PHP conf file using the PHP 5.4 internal server?