Know the open ports on Linux

Know the open ports

[root@lin-cli-141 /]# nmap -sT -O localhost

Starting nmap 3.70 ( http://www.insecure.org/nmap/ ) at 2009-10-13 19:55 IST
Interesting ports on localhost.localdomain (127.0.0.1):
(The 1649 ports scanned but not shown below are in state: closed)
PORT      STATE SERVICE
7/tcp     open  echo
22/tcp    open  ssh
23/tcp    open  telnet
25/tcp    open  smtp
80/tcp    open  http
111/tcp   open  rpcbind
443/tcp   open  https
631/tcp   open  ipp
642/tcp   open  unknown
3389/tcp  open  ms-term-serv
32770/tcp open  sometimes-rpc3
Device type: general purpose
Running: Linux 2.4.X|2.5.X|2.6.X
OS details: Linux 2.5.25 - 2.6.3 or Gentoo 1.2 Linux 2.4.19 rc1-rc7)
Uptime 8.071 days (since Mon Oct  5 18:13:19 2009)

Nmap run completed -- 1 IP address (1 host up) scanned in 2.182 seconds