By default Rancher.io launches using an embedded H2 database. This is for simplicity as this approach is sufficient for small deployments of Rancher. To switch to MySQL the following [[Settings|https://github.com/rancher/rancher/wiki/Setup:-Settings]] must be set.
db.cattle.database=mysql
db.cattle.username=cattle
db.cattle.password=cattle
db.cattle.mysql.host=localhost
db.cattle.mysql.port=3306
db.cattle.mysql.name=cattle
All values above are the defaults except db.cattle.database. If the defaults are fine, then all you need to set is db.cattle.database=mysql.