# connect to mariadb/mysql server on localhost
mysql -u root -p
# create database, create user, set password!, give permissions on this database to this user only from localhost
create database owncloud_db;
create user ownclouduser@localhost identified by 'super-secure-password';
grant all privileges on owncloud_db.* to ownclouduser@localhost identified by 'super-secure-password';
flush privileges;
# leave mariadb/mysql server
quit;