diff -ur roundcubemail-1.4.0.orig/program/include/iniset.php roundcubemail-1.4.0/program/include/iniset.php
--- roundcubemail-1.4.0.orig/program/include/iniset.php	2019-11-09 21:13:25.000000000 +0100
+++ roundcubemail-1.4.0/program/include/iniset.php	2019-11-10 10:56:06.217671159 +0100
@@ -28,7 +28,7 @@
 }
 
 if (!defined('RCMAIL_CONFIG_DIR')) {
-    define('RCMAIL_CONFIG_DIR', getenv('ROUNDCUBE_CONFIG_DIR') ?: (INSTALL_PATH . 'config'));
+    define('RCMAIL_CONFIG_DIR', getenv('ROUNDCUBE_CONFIG_DIR') ?: '/etc/roundcubemail');
 }
 
 if (!defined('RCUBE_LOCALIZATION_DIR')) {
[1]+  Done                    geany roundcubemail-1.4.0/program/include/iniset.php:30