When we need change the port, most of the time, it just need edit server.xml <pre> <Connector port=“8080” protocol=“HTTP/1.1” connectioTimeout=“20000” URIEncoding=“UTF-8”

             redirectPort="8443" />

</pre>

But when I want to change it to 80, the tomcat can't start successfully. The tomcat doesn't support the port lower than 1024, so it need do some special work

vim /etc/default/tomcat6 
AUTHBIND=yes

But this also not work on my vps, maybe the memory is not enough.

So the last solution is redirect to request on port 80 to 8080

sudo /sbin/iptables -t nat -I PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 8080

Horray, then it works.

refer to:http://stackoverflow.com/questions/4756039/how-to-change-the-port-of-tomcat-from-8080-to-80