cheatsheet

Find which process is using a specific port 8080:

lsof -i :8080

lists processes listening on TCP port 8082, showing clean output

lsof -nP -iTCP:8080 -sTCP:LISTEN

Option	What It Does
lsof	Lists open files (including network sockets)
-n	Don’t resolve IPs to hostnames (faster, no DNS delay)
-P	Don’t convert port numbers to names (e.g. show 8082 instead of us-cli)
-iTCP:8082	Filter: only show TCP connections on port 8082
-sTCP:LISTEN	Filter: only show listening sockets (not established connections)

detailed information about the process with PID ( using wide output (no truncation).)

ps -p 123 -ww

-ww: Show full command line without cutting off arguments (double w means no truncation at all)

lists all running Java processes with their PID and main class or jar file.

jps -l

shows which IP/port the Java process(pid=12345) is listening on

lsof -nP -p 12345 -iTCP -sTCP:LISTEN

List all open network ports (Java or not)

lsof -nP -iTCP -sTCP:LISTEN
or 
netstat -anp tcp

show both TCP and/or UDP

lsof -i
lsof -iTCP
lsof -iUDP

Check UDP Connectivity via nc (netcat): see the message, UDP is open.

listener: listen on my port 1234
nc -u -l -p 1234

publisher: send msg to listener ip:port
echo "test" | nc -u <listener_public_ip> 1234