Nmap Command in Linux with Examples

Nmap is Linux command-line tool for network exploration and security auditing. This tool is generally used by hackers and cybersecurity enthusiasts and even by network and system administrators. It is used for the following purposes:

  • Real time information of a network
  • Detailed information of all the IPs activated on your network
  • Number of ports open in a network
  • Provide the list of live hosts
  • Port, OS and Host scaning

Installing Nmap Command

In case of Debian/Ubuntu

sudo apt-get install nmap

In case of CentOS/RedHat

yum install nmap

Working with Nmap Command

1. To scan a System with Hostname and IP address. First, Scan using Hostname

nmap www.geeksforgeeks.org

scan-with-hostname-nmap



Now let’s Scan using IP Address

nmap 172.217.27.174

scan-with-ip-nmap.png

The nmap command allows scanning a system in various ways. In this we are performing a scan using the hostname as “geeksforgeeks” and IP address “172.217.27.174”, to find all open ports, services, and MAC addresses on the system.

2. To scan using “-v” option.

nmap -v www.geeksforgeeks.org

nmap-v-option

It is used to get more detailed information about remote machine.

3. To scan multile hosts

nmap 103.76.228.244 157.240.198.35 172.217.27.174

to-scan-multiple-host



We can scan multiple hosts by writing IP addresses or hostnames with nmap.

4. To scan whole subnet

nmap 103.76.228.*

We can scan a whole subnet or IP range with nmap by providing “*” with it. It will scan a whole subnet and give the information about those hosts which are Up in the Network.

5. To scan to detect firewall settings.

sudo nmap -sA 103.76.228.244

nmap-firewall-settings

Detecting firewall settings can be useful during penetration testing and vulnerability scans. To detect it we use “-sA” option. This will provide you with information about firewall being active on the host. It uses an ACK scan to receive the information.

6. To identify Hostnames

sudo nmap -sL  103.76.228.244

to-identify-hostnames-nmap

We use “sL” option to find hostnames for the given host by completing a DNS query for each one. In addition to this “-n” command can be used to skip DNS resolution, while the “-R” command can be used to always resolve DNS.

7. To scan from a file

nmap -iL input.txt

scan-from-file-nmap

If we have a long list of addresses that we need to scan, we can directly import a file through the command line. It will produce a scan for the given IP addresses.

8. To get some help

nmap -h

nmap-help1

nmap-help2

We use the “-h” option if we have any questions about nmap or any of the given commands. It shows the help section for nmap command, including giving information regarding the available flags.

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