Registry assignments, software defaults and local listeners are different things. A port number alone does not identify or secure a service.
Software Using This Port (2 software)
Community software entries: links are references, not individual verification.
Nrpe Nagios
Nagios Remote Plugin Executor
Usage Suggestions
- Before using port 5666, please confirm it is not occupied by other services
- If you encounter port conflicts, consider using other ports or stopping the occupying service
Frequently asked questions
What is port 5666 used for?
Port 5666 sits in the System category. This page lists the registered purpose and the software commonly associated with it; to see what is actually listening on a specific machine, check the process with ss/netstat.
Is port 5666 TCP or UDP?
The registered protocol on this page is TCP. The same number behaves independently on each protocol: TCP may be listening while UDP is idle, so check them separately.
How do I check if port 5666 is in use?
On Linux: sudo ss -tlnp 'sport = :5666' for an exact port match. On macOS: sudo lsof -nP -iTCP:5666 -sTCP:LISTEN. On Windows PowerShell: Get-NetTCPConnection -LocalPort 5666 -State Listen. A listener counts as confirmed only when you can see the bind address and process name; without root/admin you will not see other users' processes.
Is port 5666 secure? Should I open it in my firewall?
A port number has no inherent security — it depends on whether the listening service is correctly configured and whether it needs exposure at all. Keep loopback/internal-only services firewalled; where public access is required, pair it with source restrictions, VPN or authentication.
Quick Info
- Port
- 5666
- Protocol
- TCP
- Categories
- System
- Usage Status
- 2 software in use
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