nmap - port scanner

When surfing internet, somebody mentioned nmap - a powerful port scanning program.

$ sudo apt-get install nmap

$ nmap -A localhost

Starting Nmap 4.76 ( http://nmap.org ) at 2009-05-26 22:48 CST
Warning: Hostname localhost resolves to 2 IPs. Using 127.0.0.1.
SCRIPT ENGINE: '/usr/share/nmap/scripts/dns-test-open-recursion.nse' threw a run time error and could not be loaded.
SCRIPT ENGINE: '/usr/share/nmap/scripts/skype_v2-version.nse' threw a run time error and could not be loaded.
SCRIPT ENGINE: error while initializing script rules:
/usr/share/nmap/scripts/script.db:20: rpcinfo.nse is not a file!
stack traceback:
 [C]: in function 'Entry'
 /usr/share/nmap/scripts/script.db:20: in main chunk
 [C]: ?
 [C]: ?

SCRIPT ENGINE: Aborting script scan.
Interesting ports on localhost (127.0.0.1):
Not shown: 995 closed ports
PORT     STATE SERVICE     VERSION
80/tcp   open  http        Apache httpd 2.2.11 ((Ubuntu) PHP/5.2.6-3ubuntu4.1 with Suhosin-Patch)
139/tcp  open  netbios-ssn Samba smbd 3.X (workgroup: WORKGROUP)
445/tcp  open  netbios-ssn Samba smbd 3.X (workgroup: WORKGROUP)
631/tcp  open  ipp         CUPS 1.3.9
3306/tcp open  mysql       MySQL 5.0.75-0ubuntu10

Service detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 11.25 seconds
$