https://www.cyberciti.biz/faq/linux-port-scanning/ Check if a port is open nc -z -v -w5 <host> <port/range>
-w5: 5s timeout is optional
Example:
nc -zv domain 1-1023
nc -zv domain 443
nc -zv domain 80
nc -zv domain 22
nc -zv domain 21
nc -zv domain smtp
nc -zvn domain ftp |
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