If you look at source files, you'll see near the top a line that includes the following text: shim: dbms-augmented command interpreter for Interactive Brokers' tws api. Mention of the dbms is by design. The supporting database is fundamental to use of the shim, since it's the only way that the shim command language can be simplified beyond that used by the tws api.
Currently the only dbms system that works with the shim is MySQL. Although this may change in the future, for now, you must have mysql installed on your system to use the shim. Given a reasonable linux distribution, MySQL is just a package away, so what follows expects you to have a MySQL server available to you.
Current development of the shim takes place against a 5.0 series MySQL, which is important due to its support for foreign key dependency checking with InnoDB tables. The version of your server should not be an issue unless you are running a very much out-of-date system, in which case you should consider upgrading your MySQL server, and realize otherwise that use with a 4.x server is unsupported.
Bill Pippin 2010-01-14