nmap Command in Linux: Scan Networks and Ports

Quick take: The nmap command scans hosts and networks to discover live systems, open ports, and running services. nmap host does a basic scan; -sV detects service versions and -p targets specific ports. Only scan systems you own or are authorised to test.

Introduction

The nmap command (network mapper) is the standard tool for discovering hosts and the services they run. Administrators use it to audit their own networks — confirming which ports are open, what is listening, and whether anything unexpected is exposed. Always scan only systems you own or have explicit permission to test.

Syntax

The basic syntax of the nmap command is:

nmap [SCAN TYPE] [OPTIONS] TARGET

Common Options and Parameters

The most useful options and parameters for the nmap command:

Practical Examples

Real nmap commands you can run today:

# Basic scan of a host
nmap 192.168.1.10
# Discover live hosts on a subnet
nmap -sn 192.168.1.0/24
# Detect service versions
nmap -sV 192.168.1.10
# Scan specific ports
nmap -p 22,80,443 example.com
# Scan all ports, show only open
nmap -p- --open 192.168.1.10
# Audit your own server thoroughly
sudo nmap -A 192.168.1.10

Tips and Best Practices

• Only scan hosts and networks you own or are explicitly authorised to test — unsolicited scanning can violate policies and laws.
• nmap -sn 192.168.1.0/24 is a quick way to inventory the live devices on your local network.
• Use -sV to confirm that the service on a port is what you expect — handy for spotting forgotten or misconfigured services.

Final Thoughts

nmap is the go-to tool for auditing your own networks — discovering hosts, mapping open ports, and identifying services so you can close what should not be exposed. Learn -sn for host discovery, -p for port selection, and -sV for service detection, and always confine scanning to systems you are authorised to test. It pairs naturally with ss for local checks.