Date: 2019sep20 Update: 2025jun30 Product: nmap Keywords: port scan, ports Q. nmap: check if a TCP port is open/filtered/closed/etc A. Use `nmap`. Here we are just scanning port 80 on the local machine:

nmap localhost -p 80

Example output:

Starting Nmap 7.92 ( https://nmap.org ) at 2025-06-30 12:05 EDT Nmap scan report for localhost (127.0.0.1) Host is up (0.000072s latency). Other addresses for localhost (not scanned): ::1 PORT STATE SERVICE 80/tcp open http Nmap done: 1 IP address (1 host up) scanned in 0.04 seconds

In the STATE column it will report this states:

open closed filtered unfiltered open|filtered closed|filtered

For more info https://nmap.org/book/man-port-scanning-basics.html