Port 347: Fatmen Server — The Forgotten File Finder of Particle Physics

What Port 347 Was For

Port 347 is officially assigned to "fatserv"—the Fatmen Server.¹ FATMEN stands for "File and Tape Management: Experimental Needs," a distributed file catalog system developed at CERN in the early 1990s.²

The system let physicists query a file database using Unix-like commands to locate experimental data scattered across tape robots and disk storage systems. When you needed to find a specific dataset among the terabytes generated by particle accelerator experiments, you queried FATMEN through port 347.

This was infrastructure for managing physics data at the scale of "37 GB transferred in July 1993"—which sounds quaint now but was substantial then.³

The CERN Context

Port 347 belongs to a specific moment in computing history: CERN in the 1990s. The same place, the same years when Tim Berners-Lee was inventing the World Wide Web and HTTP.

While HTTP was spreading across the Internet, FATMEN was solving a different problem: how do you organize and access experimental data distributed across multiple systems, storage media, and continents? The physicists needed both—a way to share documents (HTTP) and a way to find files (FATMEN).

One protocol changed everything. The other got port 347 and a place in the archive.

How FATMEN Worked

FATMEN was designed around a layer model. The command interface was based on Unix conventions. The key feature was accessing data through a "generic name"—a Unix-like path that abstracted away where the file physically lived (which tape, which robot, which facility).⁴

The system provided:

• A worldwide distributed file catalog
• System-independent and medium-independent access to data
• Integration with CERN's tape management infrastructure

When an experiment generated data, FATMEN tracked it. When a physicist needed that data months later, FATMEN knew which tape to mount and which robot to ask.

What Happened to FATMEN

The scale of physics experiments grew exponentially. The Large Hadron Collider generates data at a scale that makes 1990s numbers look trivial—exceeding seven billion files across hundreds of distributed computing sites worldwide.⁵

Modern systems like Rucio replaced FATMEN. The file catalog problem got harder, the solutions got more sophisticated, and port 347 became a historical marker.

Port 347 Today

Port 347 sits in the well-known port range (0-1023), reserved for system services assigned by IANA through formal procedures. It's still officially registered to fatserv, but the service it was registered for no longer runs on production networks.

Some security tools have flagged port 347 as occasionally used by malware, but this is true of many abandoned ports—if nobody's using a port legitimately, it's available for illegitimate use.⁶

If you see traffic on port 347 today, it's not FATMEN. FATMEN's descendants have different names, different protocols, and different ports.

Checking Port 347

To see if anything is listening on port 347 on a Unix-like system:

# Check if port 347 is listening
sudo lsof -i :347

# Or using netstat
netstat -an | grep 347

# Check for active connections
sudo ss -tuln | grep 347

On modern systems, you'll likely find nothing. Port 347 is quiet now.

Why This Port Matters

Not because of what runs on it today—nothing does. But because it represents something true about the Internet's nervous system: the port registry is an archaeological record.

Every assigned port was assigned for a reason. Someone had a problem, built a protocol, requested a port number, and got one. Port 347 was for finding files at CERN. Port 80 was for sharing documents. One protocol we still use billions of times per day. The other we remember only when we look up port 347.

The difference between a port that changes the world and a port that becomes a footnote isn't always obvious at the time of assignment.

Related Ports

• Port 80: HTTP—the other CERN protocol from the same era, the one that survived
• Port 346: Unassigned in IANA registry, Fatmen Server's numerical neighbor
• Port 348: Unassigned in IANA registry
• Ports 1024-49151: Registered Ports range, used for user applications and less common services