I struggled a bit with getting plastic working with Firebird under Linux, so I thought I'd post the Caramilk secret in hopes it might save someone else some time.
First off, it is unclear whether the embedded db is included (it is not, Plastic uses SQLLite now).
So, the first step is to install Firebird.
The Plastic administrator's guide says:
To use Firebird, create a file called db.conf, with this content:
<DbConfig>
<ProviderName>firebird</ProviderName>
<DatabasePath>c:\myRepositoryStore</DatabasePath>
</DbConfig>
which, of course, does not work.
The correct config is:
<DbConfig>
<ProviderName>firebird</ProviderName>
<DatabasePath>/path/to/myRepositoryStore</DatabasePath>
<ConnectionString>
ServerType=0;Server=localhost;Port=3050;User=ozzy;Password=harriet;Database={0};Pooling=true;Connection Timeout=120;Connection Lifetime=1200;
</ConnectionString>
</DbConfig>
Also, the directory /path/to/myRepositoryStore must be writable by the firebird user, so:
chown firebird.firebird /path/to/myRepositoryStore
Once you have made these changes, restart Plastic, and you should see a firebird database (fdb file) appear in /path/to/myRepositoryStore
I hope this is helpful.