If you start Geronimo from a location other than the main assembly or distribution directory, Tomcat fails to start. It appears to look for var/catalina under the current working directory instead of under GERONIMO_HOME. I believe the ServerInfo can provide the GERONIMO_HOME directory if it's not otherwise available.
- build the assembly module
- go to geronimo/modules/assembly
- edit target/geronimo-1.0-SNAPSHOT/var/config/config.list and add org/apache/geronimo/Tomcat as the last line
- run java -jar target/geronimo-1.0-SNAPSHOT/bin/startup.jar