Port 562: chshell — A forgotten protocol from the Internet's early days

Port 562 holds an official assignment. It belongs to a protocol called chshell (with the service name "chcmd"). But if you've never heard of it, you're not alone. This is one of hundreds of ports in the well-known range that were assigned to protocols that never caught on—or have long since been replaced.

What is chshell?

Chshell (channel shell/channel command) was assigned port 562 for both TCP and UDP in the early 1990s, appearing in RFC 1700—the last comprehensive "Assigned Numbers" RFC published in October 1994.¹ The protocol was intended to provide some form of remote shell or command execution capability, similar in concept to other remote access protocols of that era.

But unlike SSH (port 22) or even the older rsh (remote shell), chshell never achieved widespread adoption. There are no known implementations in common use today. No major operating systems ship with chshell clients or servers. The protocol exists primarily as a line item in the IANA registry—a permanent reservation for a service that no longer answers.

The well-known port range

Port 562 sits in the well-known port range (0-1023), also called system ports or privileged ports. These are ports assigned by IANA to specific services, and on Unix-like systems, only root can bind to them.

This range was meant to be the definitive directory of Internet services. But many assignments from the 1990s turned out to be optimistic. Protocols that seemed important at the time—or protocols that someone hoped would become important—were given permanent assignments. The Internet moved on. The assignments remained.

Why unassigned and obsolete ports matter

You might wonder: why keep the assignment? Why not free up port 562 for something else?

The answer is stability. Once a port is assigned—even to a protocol no one uses—changing that assignment could cause problems. Someone, somewhere, might still be running old software that expects chshell on port 562. Or they might have written custom code that uses that port, assuming it was "theirs" because nothing else claimed it.

So the IANA registry becomes a kind of archaeological record. You can read through the well-known ports and see the history of what people thought the Internet would need. Some of those predictions were right (HTTP on port 80, HTTPS on port 443). Some were wrong. Port 562 is one of the wrong ones.

Checking what's on port 562

Even though chshell is effectively dead, a port is just a number. Any application can listen on port 562 if it wants to.

To see if anything is listening on port 562 on your system:

On Linux or macOS:

sudo lsof -i :562

Or:

sudo netstat -tuln | grep 562

On Windows:

netstat -an | findstr :562

Most of the time, you'll find nothing. Port 562 is usually silent.

What "official assignment" means

Port 562 is officially assigned to chshell.² That means:

• IANA recognizes chshell as the designated service for this port
• Applications shouldn't use port 562 for other purposes (in theory)
• The assignment is permanent unless IANA explicitly changes it

But "official" doesn't mean "used." The well-known port range is full of ghosts—protocols that once seemed important enough to reserve a spot in the registry, but never found a place in the actual Internet.

Port 562 is one of them. A reminder that not every door in the Internet's address space leads somewhere. Some doors were built for rooms that were never finished.