9100
Prometheus Node Exporter — exposes host system metrics
Prometheus Node Exporter
What is port 9100?
Port 9100 is used by the Prometheus Node Exporter, which exposes detailed system-level metrics (CPU, memory, disk I/O, network) via an HTTP endpoint for Prometheus to scrape. Almost every Linux server in a Prometheus monitoring ecosystem runs Node Exporter. If exposed to the internet, it reveals detailed hardware and OS information that aids in reconnaissance.
Quick checks
$
nc -zv example.com 9100
$
nmap -p 9100 example.com
$
telnet example.com 9100