Port 873 (TCP) — rsync daemon

Check if port 873 is open

On the server, see what is listening:

sudo ss -tulpn | grep ':873 '

From another machine, test reachability:

nc -zv your-server.example.com 873

Block port 873 from the internet

With UFW (Ubuntu/Debian):

sudo ufw deny 873

With firewalld (RHEL/AlmaLinux/Rocky):

sudo firewall-cmd --permanent --remove-port=873/tcp && sudo firewall-cmd --reload

← All common ports