Port 8081 HTTP alt · TCP

What runs on port 8081

The "second" alternative HTTP port: Nexus Repository, McAfee ePO, Sonatype, the admin side of several apps that serve on 8080 (Jenkins agents, some Spring Boot actuators), and Node/Metro bundlers. Nothing standard; identify the process.

Software that uses it: Sonatype Nexus · React Native Metro · various admin/secondary interfaces

Should port 8081 be open?

Internet-facing only with authentication and care. It can be exposed when the service behind it is authenticated, rate-limited and kept up to date; most deployments are better off behind a VPN, an allow-list or a reverse proxy.

• ss -ltnp | grep :8081 names it on Linux; on Windows, netstat -ano | findstr :8081 then tasklist /fi "pid eq N".

Check port 8081

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :8081'
sudo lsof -i :8081

# from another machine: is it reachable?
nc -zv host 8081
nmap -p 8081 host
curl -v telnet://host:8081      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 8081

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 8081 proto tcp
sudo ufw deny 8081/tcp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 tcp dport 8081 accept
nft add rule inet filter input tcp dport 8081 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 8081 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 8081 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=8081 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 8081" with no source is just "open".

Putting it behind nginx

server {
    listen 443 ssl;
    server_name app.example.com;
    location / {
        proxy_pass http://127.0.0.1:8081;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
    }
}

Then make the application listen on 127.0.0.1:8081 only. Test which location block a request hits with the nginx location tester.

Related ports

• 8080 HTTP alt — Tomcat, proxies, dev servers
• 8443 HTTPS alt — Tomcat, Plesk, Unifi

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions