What does the -O option do in Nmap?

What does the -O option do in Nmap?

• A. Enable operating system detection.
• B. Enable banner grabbing.
• C. Enable OS detection with some extra heuristics.
• D. Enable all script scanning.

Answer: (A)

OS fingerprinting is what the -O option enables in Nmap. It works by sending a set of probes and analyzing how the target’s TCP/IP stack replies—looking at factors like TTL, window size, and IP identification—to infer the operating system. This is separate from banner grabbing or service version detection. Banner grabbing and version info come from other features, while -O specifically focuses on guessing the OS. If you want a broader scan that also includes versions and scripts, you’d use the aggressive option (-A). Note that OS detection can require root privileges on some systems and may be affected by firewalls or network middleboxes.

OS fingerprinting is what the -O option enables in Nmap. It works by sending a set of probes and analyzing how the target’s TCP/IP stack replies—looking at factors like TTL, window size, and IP identification—to infer the operating system. This is separate from banner grabbing or service version detection. Banner grabbing and version info come from other features, while -O specifically focuses on guessing the OS. If you want a broader scan that also includes versions and scripts, you’d use the aggressive option (-A). Note that OS detection can require root privileges on some systems and may be affected by firewalls or network middleboxes.