nmap
Basic usage:
nmap hackme.org
With service detection at the maximum intensity over all ports and verbose logging:
nmap -vv -p- -sV --version-intensity 9 hackme.org
An alternative approach suggested by no other but nmap.org:
Increase -T4 to -t5 for faster scan.
sudo nmap -vv -p- -sSV -O -T4 hackme.org
Scan ports only (stealth):
sudo nmap -vv -p- -sS -T5 hackme.org
Other options:
-p- : Scan for all 65535 ports
-sU : UDP connect scan
-sT : TCP connect scan
-O : Scans for operating system running
-v : Verbose scan
-A : Aggressive scan, scans for everything
-T[1-5] : To set the scanning speed
-Pn : In case the server blocks ping