I tried with this in /storage/.kodi/userdata/addon_data/service.mariadb/my.cnf and I got log file with bunch of lines from Kodi.
/storage/.kodi/addons/service.mariadb/bin/mysqld, Version: 10.3.11-MariaDB-log (MariaDB Server). started with:190110 13:07:30 8 Connect [email protected]<IP_REMOVED> as anonymous on
start/stop/restart the mariadb service
Kodi user can't connect on localhost but only on real ip address. That's why you need to use -h parameter
I assume user [email protected] doesn't even exist according to what is created: LibreELEC.tv/mariadb.start at master · LibreELEC/LibreELEC.tv · GitHub
I'm not mysql user so something can also be wrongly implemented.