This problem occurs because when core.php is loaded the config file has not been read yet. So if you set $g_core_path in /config/config_inc.php the variable is still not defined at that moment.

A work around is to move the whole core directory to an outside path. Then recreate the core folder and copy the file constant_inc.php to that newly created core folder from the outside path core folder. This will result in an empty core folder that only contains constant_inc.php.

You can also move the config folder to the outside location. And then you have to still keep the config folder and /config/config_inc.php. But you can edit that new config and change its content to only the paths and the include_once( $g_config_path . 'config_inc.php' ).

Here is the snippet:
<?php
$g_config_path = '/opt/mantisbt_outside/config/';
$g_core_path = '/opt/mantisbt_outside/core/';
$g_class_path = '/opt/mantisbt_outside/core/classes/';
$g_library_path = '/opt/mantisbt_outside/library/';
$g_language_path = '/opt/mantisbt_outside/lang/';

include_once( $g_config_path . 'config_inc.php' );

Hope this helps anybody who had the same problem.

I tried this with 2.11.1 but when I tried to go to the login page, I get a blank. only when I put the config back in the mantisbt root directory does this work. This also happens when i move the core as well. Please advise as to what I could be doing wrong.

Note the variable $ t_local_config = getenv ('MANTIS_CONFIG_FOLDER') in config_defaults_inc.php

It extracts the path to your "config" folder from the environment variable of your web server.
Add the following line to your web server's configuration file:
SetEnv MANTIS_CONFIG_FOLDER /path to your config folder/

Indeed, there is a problem. Sorry...

still there in 2.24.1

Even if one updates the variables to point to the outside, apparently path to "core" folder is hardcoded at https://github.com/mantisbt/mantisbt/blob/master/core.php#L67, so it makes no sense to copy core folder outside of webroot.

Update: found several more hardcoded paths:

• https://github.com/mantisbt/mantisbt/blob/master/core/commands/IssueAddCommand.php#L36
• Lang check in admin checks

=> so those checks don't make any sense now, there is no way to fix them. Please remove them until it's possible to make them green without dirty hacks.

I've just run into this too updating to 2.24.1. (Also I don't recall this warning in previous versions.)

Just as a datapoint: I installed a fresh 2.25.2 on a fresh server and saw this again.