A few Important Nmap scans are as given below

nmap -sS

only first step of the tcp handshake is done which is sending SYN and as a result you are a little undetectable.

The target can send back syn/ack which tells the port is open

it can also send rsd which means port is closed

if no response then filtered

filtered port means either there is a packet filtering firewall or a normal firewall ....

nmap -sT

Does not require sudo privileges

It performs scan using tcp packets

A total 3 way tcp handshake is done

Will remain fingerprints and traces on the target and easily detectable.

Can take a little bit longer

nmap -sU

Since many service on internet run on tcp, udp is mostly ignored.

Which can be helpful to us.

This scan can be helpful to us but is a bit slow.

Requires root privileges

To see all other nmap scans see nmap's manual

can be done using man command

man nmap

A screen grab for the upper command is as given below

As well as port states and other details

TARGET SPECIFICATIONS

HOST DISCOVERY

SCAN TECHNIQUES

Ethical Hacking