Port 5900: VNC

What is port 5900 used for?

Virtual Network Computing remote desktop.

Should port 5900 be open?

Don’t expose to the internet. Keep this port on private networks and reach it through a VPN or SSH tunnel. Many VNC servers have weak passwords. Tunnel VNC through SSH or a VPN.

See what is listening on port 5900

# Linux
sudo ss -tlnp | grep ':5900 '

# macOS
sudo lsof -nP -i TCP:5900 -sTCP:LISTEN

# Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5900 -State Listen

Open or block port 5900 in a firewall

# Ubuntu / Debian (ufw)
sudo ufw allow 5900/tcp
sudo ufw deny 5900/tcp

# Windows (PowerShell, as administrator)
New-NetFirewallRule -DisplayName "Port 5900" -Direction Inbound -Protocol TCP -LocalPort 5900 -Action Allow

On cloud servers, also open the port in the provider’s security group or network firewall. At home, a service behind a router needs a port-forwarding rule to the device’s local IP.

Test it from outside

A port can be open on the server but blocked upstream. The Port Checker connects from the internet, so it shows what the world sees. From your own machine, use nc -vz example.com 5900 (macOS/Linux) or Test-NetConnection example.com -Port 5900 (Windows).