Auditing listening services

Articles

• ss — sockets and ports — Shows who is listening on ports and which connections are open; a netstat replacement, faster with many connections.
• nmap: which ports are visible from outside — A port scanner: shows which ports of a machine are open, closed or filtered, as another machine sees them.
• nc — checking ports and transferring data — Checking whether ports are reachable, simple data transfer over TCP/UDP.
• conntrack — connection tracking — The kernel's connection table — what NAT/firewall see, overflow, debugging.
• Firewall — nftables / ufw — A mechanism filtering network traffic according to specified conditions and actions.
• PostgreSQL — access, pg_hba.conf, dump and restore — PostgreSQL is a relational DBMS: roles and databases, pg_hba.conf access rules, pg_dump dumps and pg_restore restores.