Find list of open ports / listening ports

lsof

Samples 

 # lsof -i -n -P

netstat

Samples

# netstat -tulpn

# netstat -a | egrep 'Proto|LISTEN'

# netstat -ao

Important netstat arguments

-n, --numeric           don't resolve names - this one really saves time ;)

-e, --extend            display other/more information

-p, --programs          display PID/Program name for sockets

-l, --listening         display listening server sockets

-t, --tcp   tcp

-u, --udp   udp

-a, --all, --listening  display all sockets (default: connected)

-c, --continuous        continuous listing