If you are experiencing an error during the first Setup of Retain when using a Mysql-Database:
"An error occurred configuring database: Failure to acquire Enterprise DB Connection."
You 've missed installing the MySQL-Connector-J library.
You can find it here: "https://dev.mysql.com/downloads/connector/j/"
After you've downloaded and unpacked the mysql-connector-java-5.1.X.jar you should copy the file to the following directories:
Next the tomcat-user needs to have group access to those files.
Therefore you can either run
$ chown tomcat:www <filename>
or do this via the Graphical User interface and Assign the owner to tomcat and the group to WWW.
After you've done these steps restart the retain service with:
$ rcretain-tomcat7 restart
The Connection to the Database should be working now.