Find Open/Listening Ports on Linux & FreeBSD

There are different commands on both Linux and UNIX server to find out what tcp/udp ports are listening or open on your own server. You can use netstat command, which print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships etc. Another (and suggested) option is to use lsof command, which list open files, and ports on Linux, FreeBSD, Solaris and other Unixish systems.

netstat command to find open ports

# netstat --listen
To display open ports and established TCP connections, enter:
$ netstat -vatn
To display only open UDP ports try the following command:
$ netstat -vaun
If you want to see FQDN (full dns hostname), try removing the -n flag:
$ netstat -vat

lsof Command Examples

To display the list of open ports, enter:

# lsof -i
To display all open files, use:
# lsof
To display all open IPv4 network files in use by the process whose PID is 9255, use:
# lsof -i 4 -a -p 9255

FreeBSD Users

Use the sockstat command on FreeBSD as follows:

$ sockstat
$ sockstat -l
$ sockstat -4 -l
$ sockstat -6 -l