Nmap CLI Playbook

Official docs:

• https://nmap.org/book/man-briefoptions.html
• https://nmap.org/book/man.html
• https://nmap.org/book/man-performance.html

Canonical syntax: nmap [Scan Type(s)] [Options] {target specification}

High-signal flags:

• -n skip DNS resolution
• -Pn skip host discovery when ICMP/ping is filtered
• -sS SYN scan (root/privileged)
• -sT TCP connect scan (no raw-socket privilege)
• -sV detect service versions
• -sC run default NSE scripts
• -p <ports> explicit ports (-p- for all TCP ports)
• --top-ports <n> quick common-port sweep
• --open show only hosts with open ports
• -T<0-5> timing template (-T4 common)
• --max-retries <n> cap retransmissions
• --host-timeout <time> give up on very slow hosts
• --script-timeout <time> bound NSE script runtime
• -oA <prefix> output in normal/XML/grepable formats

Agent-safe baseline for automation: nmap -n -Pn --open --top-ports 100 -T4 --max-retries 1 --host-timeout 90s -oA nmap_quick <host>

Common patterns:

• Fast first pass: nmap -n -Pn --top-ports 100 --open -T4 --max-retries 1 --host-timeout 90s <host>
• Very small important-port pass: nmap -n -Pn -p 22,80,443,8080,8443 --open -T4 --max-retries 1 --host-timeout 90s <host>
• Service/script enrichment on discovered ports: nmap -n -Pn -sV -sC -p <comma_ports> --script-timeout 30s --host-timeout 3m -oA nmap_services <host>
• No-root fallback: nmap -n -Pn -sT --top-ports 100 --open --host-timeout 90s <host>

Critical correctness rules:

• Always set target scope explicitly.
• Prefer two-pass scanning: discovery pass, then enrichment pass.
• Always set a timeout boundary with --host-timeout; add --script-timeout whenever NSE scripts are involved.
• Keep discovery scans tight: use explicit important ports or a small --top-ports profile unless broader coverage is explicitly required.
• In sandboxed runs, avoid exhaustive sweeps (-p-, very high --top-ports, or wide host ranges) unless explicitly required.
• Do not spam traffic; start with the smallest port set that can answer the question.
• Prefer naabu for broad port discovery; use nmap for scoped verification/enrichment.

Usage rules:

• Add -n by default in automation to avoid DNS delays.
• Use -oA for reusable artifacts.
• Prefer -p 22,80,443,8080,8443 or --top-ports 100 before considering larger sweeps.
• Do not use -h/--help for routine usage unless absolutely necessary.

Failure recovery:

• If host appears down unexpectedly, rerun with -Pn.
• If scan stalls, tighten scope (-p or smaller --top-ports) and lower retries.
• If scripts run too long, add --script-timeout.

If uncertain, query web_search with: site:nmap.org/book nmap <flag>