Docker file using the latest CentOS to install MariaDB from mariadb.org's yum repo. It follows much of the path as the official MariaDB repo except it's on CentOS and it offers support for creating multiple databases on intial creation.
To specify multiple databases list them as a comma delimited string in the environment variable MYSQL_DATABASE, e.g.
MYSQL_DATABASE=database-1,database-2. At this stage any user you set up (with MYSQL_USER and MYSQL_PASSWORD) will have access to all the databases that are created.
Otherwise uses the same environment variables as the official MariaDB dockerfile.
NB. If you want to run mysql in the container for testing, you'll need to set the term environment variable first,
export TERM=dumb then run
mysql as discussed here