A really quick one tonight. It will be nice to actually have some time soon to expound more on these things as this semester winds down (and maybe only one more to finish the Masters!)
Sometimes I want to konw what ports are listening on a server. I can use this information to help troubleshoot a non-working inbound connection or I can use this to make sure that specific ports are NOT listening. Run the below as root or using sudo:
netstat -an | grep -i listen or netstat -an | grep "LISTEN"
This command can, like every unix command I can think of tonight, can be used/piped with other commands, such as awk in order to clean-up/format the output.