nmap Command: Scan A Single IP Address or Host

How do I use nmap command to scan a single server using a host name or an IP address under Unix like operating systems?

You can use a nmap command to scan a single server using a host name such as server1.cyberciti.biz or an IP address such as 192.168.1.254. The syntax is:

Tutorial details
Difficulty	Easy (rss)
Root privileges	No
Requirements	nmap

nmap host-name-here
OR
nmap IP-address-here
This example demonstrates port scanning using an IP address:
$ nmap 192.168.1.1
This example demonstrates port scanning using a host name:
$ nmap router
Sample outputs:

Fig.01: nmap command output

Understanding nmap command output

Not shown: 998 closed ports - By default nmap will show open ports only in the following format.

PORT - Port number with protocol.
STATE -The state is either open, filtered, closed, or unfiltered. Open state means that an application on the target machine is listening for connections/packets on that port. Filtered state means that a firewall, filter, or other network obstacle is blocking the port so that Nmap cannot tell whether it is open or closed.
SERVICE The service name. For example, the port # 22 is often used by ssh service such as OpenSSH server or the port # 80 is often used by a web server such as Apache.

To scan multiple IP addresses or hosts names:
$ nmap server1 server2 server2.nixcraft.net.in $ nmap 192.168.1.1 192.168.1.2
Sample outputs:

Fig.02: nmap scan for multiple hosts

Tip: You can use nmap 192.168.1.1,2 instead of typing nmap 192.168.1.1 192.168.1.2, as both IP addresses are part of the same subnet 192.168.1.0/24.

To speed up nmap execution pass the -T4 option as follows:
$ nmap -T4 192.168.1.1