Short answer: you can't. Ports below 1024 can be opened only by root. As per comment - well, you can, using CAP_NET_BIND_SERVICE, but that approach, applied to java bin will make any java program to be run with this setting, which is undesirable, if not a security risk.
The long answer: you can redirect connections on port 80 to some other port you can open as normal user.
Run as root:
# iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 8080
As loopback devices (like localhost) do not use the prerouting rules, if you need to use localhost, etc., add this rule as well (thanks @Francesco):
# iptables -t nat -I OUTPUT -p tcp -d 127.0.0.1 --dport 80 -j REDIRECT --to-ports 8080
NOTE: The above solution is not well suited for multi-user systems, as any user can open port 8080 (or any other high port you decide to use), thus intercepting the traffic. (Credits to CesarB).
EDIT: as per comment question - to delete the above rule:
# iptables -t nat --line-numbers -n -L
This will output something like:
Chain PREROUTING (policy ACCEPT)
num target prot opt source destination
1 REDIRECT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:8080 redir ports 8088
2 REDIRECT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 redir ports 8080
The rule you are interested in is nr. 2, so to delete it:
# iptables -t nat -D PREROUTING 2
You can use udev for this. Create a file /etc/udev/rules.d/90-rename-serial-ports.rule containing
ACTION=="add" KERNEL=="ttyS2" NAME="ttyS1"
should do it (not tested). Note the difference between "==" and "=".
Best Answer
There are a few options:
sersniff is a simple program to tunnel/sniff between 2 serial ports.
Serial to Network Proxy (ser2net) provides a way for a user to connect from a network connection to a serial port.
SerialSpy acts as a serial pass-through device. It listens for incoming data on two serial ports and forwards it so the devices act as if they are directly connected. It also logs the data as it moves through the ports.
sercd is an RFC 2217-compliant serial port redirector. It lets you share a serial port through a network. It is based on sredird. The RFC2217 protocol is an extension to telnet and allows changing communication port parameters.
SerLooK is a KDE application for inspecting data going over serial lines. It can work as a binary terminal that sends and receives data through a defined port (Point to Point mode) and displays them on separate views. Each view can be configured to display data in hexadecimal, decimal, octal, binary, and raw ASCII. It is also possible to perform I/O through terminal emulation views and define a secondary port and monitor the traffic between two external hosts using a "Y" cable (Snooper mode).
nullmodem creates a virtual network of pseudo-terminals. It can be used as an adapter to connect two programs that normally need serial interface cards.
ttywatch monitors, logs, and multiplexes terminal I/O. It has full log rotation built in, and can use telnet as well as local TTY ports.
Serial line sniffer (slsnif) is a serial port logging utility. It listens to the specified serial port and logs all data going through this port in both directions.