With Synaptic:
tomcat6 tomcat6-user
Several instances of Tomcat6 can run at the same time.
tomcat6-instance-create test_instance
test_instance/bin/startup.sh
test_instance/bin/shutdown.sh
To run your instance in interactive mode (so you don't have to open the log file every time), create test_instance/bin/run.sh:
#!/bin/sh export CATALINA_BASE=/home/jerome/test_instance /usr/share/tomcat6/bin/catalina.sh run
Don't forget to change CATALINA_BASE to match your configuration.
With Tomcat 6, the shared folder has been removed from Tomcat directory. If you used to have a shared/classes directory, you can recreate it under your test_instance, and in test_instance/conf/catalina.properties:
shared.loader=${catalina.base}/shared/classes,${catalina.base}/shared/lib/*.jar