Port 21 (TCP) — FTP

File Transfer Protocol control channel.

🔒 Runs locally — your input never leaves this browser tab

Clear-text credentials. Replace with SFTP or FTPS.

Check if port 21 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':21 '

From another machine, test reachability:

nc -zv your-server.example.com 21

With UFW (Ubuntu/Debian):

sudo ufw deny 21

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=21/tcp && sudo firewall-cmd --reload