Olaf, It seems that in this case, the error log should indeed be in the datadir ($ldata -> /var/lib/mysql).
I have double checked and this behavior is the same since 10.1 (Debian or upstream). See: https://salsa.debian.org/mariadb-team/mariadb-10.1/blob/master/scripts/mysql_install_db.sh#L489 https://salsa.debian.org/mariadb-team/mariadb-10.3/blob/master/scripts/mysql_install_db.sh#L511 https://github.com/MariaDB/server/blob/10.1/scripts/mysql_install_db.sh#L499 https://github.com/MariaDB/server/blob/10.3/scripts/mysql_install_db.sh#L511 Faustin
