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netcat

Netcat can be used to scan a port without nmap. For instance:

# 5 second timeout on port 161
$ nc -vz -w 5 my.fsf.org 161
nc: connect to my.fsf.org (209.51.188.223) port 161 (tcp) timed out: Operation now in progress
nc: connect to my.fsf.org (2001:470:142:5::223) port 161 (tcp) failed: Network is unreachable

Some people consider having netcat installed to be a security risk, because it can be used to listen to and make TCP connections. However that is not the biggest part of our attack surface. It might make sense not to install it in a container though.