I have figured it out by tracing the various shortcuts in Lubuntu. Basically, it involves creating a init script in
/etc/init.d as listed in the bottom, which starts
tomcat and call the content of the osgeo geoserver start script. Note: restarting tomcat is not good enough as I had thought.
After that do:
update-rc.d myscript defaults 99 01
### BEGIN INIT INFO
# Provides: myscript
# Required-Start: $remote_fs $syslog
# Required-Stop: $remote_fs $syslog
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: Start daemon at boot time
# Description: Enable service provided by daemon.
### END INIT INFO
case "$1" in
service tomcat6 restart
-- UPDATE --
After some digging, I found that OSGeoLive (8.0) favor of GeoServer is powered by jetty, not tomcat, though both are installed. That explains why starting tomcat does not start geoserver.