All the needed configuration parameters you can/have to to are linked below. In this entry i want to point out the use of setenv.sh.
With setenv.sh you don't have to edit the default startup script from the tomcat. This means you also can backup/store your settings on a well know place and then just create a link into the directory where your catalina.sh file is placed. The catalina.sh script itself looks for a setenv.sh and reads it. Everything that is configured inside the setenv.sh script overwrites the default settings inside the catalina.sh.