Copyright 2005 Mort Bay Consulting
On Unix derived systems, due to differenced between JVMs for how their threads map to kernel processes, it is not sufficient, secure or 100% java to call setuid to change to a non-root user after opening port 80.
A better solution is to run the server on a non-privileged port (eg 8080) and use a firewall or routing mechanism to map port 80 to 8080.
On some Linux systems the ipchains REDIRECT mechanism can be used to redirect from one port to another inside the kernel:
/sbin/ipchains -I input --proto TCP --dport 80 -j REDIRECT 8080This basically means, "Insert into the kernel's packet filtering the following as the first rule to check on incoming packets: If the protocol is TCP and the destination port is 80, redirect the packet to port 8080." Your kernel must be compiled with support for ipchains. (virtually all stock kernels are.) You must have the "ipchains" command-line utility installed. (On RedHat the package is aptly named "ipchains".) You can run this command at any time, preferably just once since it inserts another copy of the rule every time you run it.
Once this rule is set up, a Linux 2.2 kernel will redirect all data addressed to port 80 to a server such as Jetty running on port 8080.This includes all RedHat 6.x distros. Linux 2.4 kernels, e.g. RedHat 7.1+, have a similar "iptables" facility.
You need to add something like the following to the startup scripts or your firewall rules:
/sbin/iptables -t nat -I PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 8080The underlying model of iptables is different to that of ipchains so the forwarding normally only happens to packets originating off-box. You will also need to allow incoming packets to port 8080 if you use iptables as a local firewall.
Be careful to place rules like this one early in your "input" chain. Such rules must precede any rule that would accept the packet, otherwise the redirection won't occur. You can insert as many rules as needed if your server needs to listen on multiple ports, as for HTTPS.
Note: For some extremely handy scripts (verified against SuSe 7.3) and a detailed readme.txt, download a the tiny tarball iptables.tgz contributed by Chris Haynes (thanks Chris!).