Scanning open ports in linux using nmap

nmap - Network exploration tool and security / port scanner

Syntax:

nmap [options] target

Scan all the open ports

$ nmap localhost       use: -F for fast scan, -p [port number] for particular port

Output:

Not shown: 993 closed ports

PORT     STATE SERVICE

21/tcp   open  ftp

22/tcp   open  ssh

25/tcp   open  smtp

80/tcp   open  http

111/tcp  open  rpcbind

631/tcp  open  ipp

3306/tcp open  mysql

Scan remote ip/host

$ nmap google.com

Starting Nmap 5.51 ( http://nmap.org ) at 2015-02-17 15:35 IST

Nmap scan report for google.com (74.125.236.36)

Host is up (0.00095s latency).

Other addresses for google.com (not scanned): 74.125.236.41 74.125.236.39 74.125.236.34 74.125.236.32 74.125.236.46 74.125.236.37 74.125.236.40 74.125.236.33 74.125.236.38 74.125.236.35

rDNS record for 74.125.236.36: maa03s04-in-f4.1e100.net

Not shown: 942 closed ports, 56 filtered ports

PORT    STATE SERVICE

80/tcp  open  http

443/tcp open  https

Scan only TCP (T) or UDP (U) or Other(O) open ports

nmap -sT localhost