Port 3306 (TCP) — MySQL / MariaDB

MySQL and MariaDB database server.

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Bind to 127.0.0.1 or a private/VPN interface. Never expose to the internet.

Check if port 3306 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':3306 '

From another machine, test reachability:

nc -zv your-server.example.com 3306

With UFW (Ubuntu/Debian):

sudo ufw deny 3306

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=3306/tcp && sudo firewall-cmd --reload