How do I verify which ports are listening in Linux?

petulia3478

Type nmap followed by the IP or hostname of the host you want to query.

# nmap 192.168.1.65

Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2009-07-21 09:24 BST
Stats: 0:00:24 elapsed; 0 hosts completed (1 up), 1 undergoing SYN Stealth Scan
SYN Stealth Scan Timing: About 2.45% done; ETC: 09:41 (0:15:54 remaining)
Stats: 0:02:00 elapsed; 0 hosts completed (1 up), 1 undergoing SYN Stealth Scan
SYN Stealth Scan Timing: About 8.35% done; ETC: 09:49 (0:22:02 remaining)
Stats: 0:20:45 elapsed; 0 hosts completed (1 up), 1 undergoing SYN Stealth Scan
SYN Stealth Scan Timing: About 75.20% done; ETC: 09:52 (0:06:50 remaining)
Interesting ports on Unknown-00-0c-29-8a-13-db.home (192.168.1.65):
Not shown: 1678 filtered ports
PORT    STATE  SERVICE
22/tcp  open   ssh
631/tcp closed ipp
MAC Address: 00:0C:29:8A:13:DB (VMware)

Nmap finished: 1 IP address (1 host up) scanned in 1675.784 seconds

If you press Enter before nmap has finished, you will get a progress report i.e. "About 8.35% done".

The above example shows that, on server 192.168.1.65, port 22 is open and ssh is listening on port 22.