Tomcat 9 is a Java webserver used for this application. The version of tomcat available for installation on Ubuntu 24.04 is Tomcat 10 only, which unfortunately is not compatible with Grails 6 applications on which this project is built. Until Grails 7 is available, and this project is upgraded to use it, I have to deploy Tomcat 9 with the application. Tomcat 9 is installed transparently from a tar file by the .deb installer with the rest of the application.