Port 10010 — Unassigned, but Claimed

What This Port Range Means

Port 10010 falls in the registered ports (1024-49151), the middle ground of the port system. These ports are available for anyone to register with IANA, but registration is optional—you can use one without asking permission. The IANA registry exists to prevent conflicts, but it's not a gatekeeper. It's a suggestion with teeth: if a service is widely used, its port gets documented. If it's not, it sits in the shadows.

Port 10010 is unassigned in the official registry. No RFC. No IANA entry. And yet services use it.

Known Unofficial Uses

Open Object Rexx (ooRexx): The rxapi daemon listens on port 10010/TCP as a network API gateway for the Open Object Rexx scripting language. ¹ It's a quiet use case—you don't encounter this unless you're working with Rexx systems, but it's documented and stable.

containerd and Docker: The containerd container runtime—the engine behind Docker—uses port 10010 internally for certain operations. ^{2 3} If you're running containerized workloads, this port may be bound on your system. The Kubernetes issue tracker shows edge cases where kubectl connections to port 10010 can fail if something else is bound there. ⁴

These aren't official uses. They're just what people needed, and port 10010 was available.

How to Check What's Listening

If you want to know what's actually using port 10010 on your machine:

On Linux/macOS:

lsof -i :10010
netstat -tulpn | grep 10010
ss -tulpn | grep 10010

On Windows:

netstat -ano | findstr :10010

The first command shows you the process name. The second shows the process ID (PID). On Windows, use Task Manager to look up the PID if you need more information.

Why Unassigned Ports Matter

Port 10010 illustrates something important about how the Internet actually works: assignment is optional. Someone can write software, pick a port number in the registered range, and start listening. No approval needed. No coordination required. The IANA registry is there to help—to say "this port is claimed, maybe don't use it"—but it's not a lock.

This creates a contract: use an unassigned port at your own risk. There's no guarantee another service won't also pick port 10010 five years later. The lack of registration means the lack of protection. ooRexx and containerd are fine here because they're rarely on the same system. But if there's a conflict, there's no arbiter. The first one to bind wins.

That's why most serious services register with IANA. Not because they have to. Because they don't want to explain in 2027 why their software won't start because some other service claimed the same port.

Port 10010 works because it's boring. No one important needs it. Yet.