After stopping the command (Ctrl + c), the new service is frozen as "restarting" and can't be remove (it is detected as stopped), so the only way to really stop its container is sudo docker stop <id>.
dokku mariadb:logs <service> returns this (repeated more than 10 times):
error: database is uninitialized and password option is not specified
You need to specify one of MYSQL_ROOT_PASSWORD, MYSQL_ALLOW_EMPTY_PASSWORD and MYSQL_RANDOM_ROOT_PASSWORD
I've traced the execution until functions#L257.
After stopping the command (Ctrl + c), the new service is frozen as "restarting" and can't be remove (it is detected as stopped), so the only way to really stop its container is
sudo docker stop <id>
.dokku mariadb:logs <service>
returns this (repeated more than 10 times):