Check which ports are listening in Linux

A reliable way to check which ports are listening is to do a port scan. The nmap command can be used for this: toro@moutere:~$ sudo nmap -sT -O localhost

Starting Nmap 4.76 ( http://nmap.org ) at 2009-03-12 20:18 NZDT
Interesting ports on localhost (127.0.0.1):
Not shown: 995 closed ports
PORT STATE SERVICE
53/tcp open domain
80/tcp open http
139/tcp open netbios-ssn
445/tcp open microsoft-ds
631/tcp open ipp
Device type: general purpose
Running: Linux 2.6.X
OS details: Linux 2.6.17 - 2.6.25
Network Distance: 0 hops

OS detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 1.63 seconds


Sources

• http://www.redhat.com/docs/manuals/linux/RHL-9-Manual/security-guide/s1-server-ports.html