Port 2833: glishd — The Telescope Daemon

What This Port Is

Port 2833 is registered with IANA under the service name glishd — the daemon process for Glish, a distributed event-driven scripting language and inter-process communication system developed for scientific computing.¹

It falls in the registered port range (1024–49151). These ports are assigned by IANA to specific applications and services. Unlike the well-known ports below 1024, registered ports don't require elevated privileges to open, and they aren't reserved at the operating system level — any process can bind to 2833. IANA registration just means someone officially claimed it.²

The assignee on record: Darrell Schiebel, a software developer at the National Radio Astronomy Observatory.

What Glish Was

Glish was built for a world where your computation was spread across dozens of machines that all needed to talk to each other in real time.

Its origin is strange. Glish was first developed at Lawrence Berkeley Laboratory for the Superconducting Super Collider — the massive particle accelerator that the United States started building in Texas in the 1980s before Congress cancelled it in 1993. The SSC needed software to coordinate distributed detector systems. Glish was part of that.³

After the SSC died, Glish found a new home. The National Radio Astronomy Observatory adopted it for AIPS++ (Astronomical Image Processing System), the software platform powering telescopes including the Very Large Array in New Mexico. Darrell Schiebel took over maintenance in 1995 and developed it throughout the AIPS++ era.⁴

In AIPS++, Glish served as both the command-line interface and the "software bus" connecting C++ computing components. Astronomers wrote Glish scripts to orchestrate data reduction pipelines — calibrating signals, removing interference, producing images of objects billions of light-years away. The glishd daemon was the process that kept this distributed system coordinated.

In 2004, AIPS++ was reorganized into CASA (Common Astronomy Software Applications), and the scripting layer switched from Glish to Python bindings. Glish was retired.⁵

Port 2833 has been quiet ever since.

Security Notes

There are no known active exploits targeting port 2833. The software it was built for is defunct. If you see unexpected traffic on this port, it warrants investigation — but it's not a known attack surface the way older legacy ports are.

Some older security databases flag it as a port "associated with malware," which is common boilerplate for any low-traffic unmonitored port that occasionally gets probed by scanners.

Checking What's on This Port

If you want to see whether anything is listening on port 2833 on your system:

macOS/Linux:

# Show what process is bound to port 2833
lsof -i :2833

# Or with ss (Linux):
ss -tlnp | grep 2833

Windows:

netstat -ano | findstr :2833

On almost any modern system, you'll find nothing. That's the expected result.

Why Unassigned (and Quiet-Registered) Ports Matter

The registered port range contains thousands of entries like this one — services that were assigned, used for a specific purpose, and then quietly abandoned as software evolved. The port number stays in the registry indefinitely. IANA doesn't reclaim them.

This matters because:

• Port scanners see them as interesting — an open port in a range that "shouldn't" have anything on it triggers alerts
• Firewall rules need context — knowing that 2833 is a dead radio astronomy daemon, not an active service, helps you make informed decisions about whether to block it
• History lives in the registry — port 2833 is a small record of the Superconducting Super Collider, the VLA, and the era when astronomers had to build their own distributed computing infrastructure before Python made it easy