Port 607: NQS — The batch scheduler that taught Unix to queue

Port 607 lives in the well-known range (0-1023), where IANA assigns ports to fundamental Internet services. It was officially assigned to NQS—the Network Queuing System—a batch processing protocol that most modern engineers have never heard of but that quietly shaped how we schedule computational work today.

What NQS Does

NQS is a network-based batch job system. In plain terms: it lets you submit computational jobs to a queue, route them across a network to available machines, and manage their execution. Think of it as the grandfather of modern job schedulers like SLURM, PBS, and LSF.¹

When a client submits a job through port 607, NQS handles:

• Accepting the job submission
• Queuing it based on priority and resource requirements
• Routing it to an appropriate compute node
• Managing execution and reporting results back

The History

In 1986, Unix systems had a problem. They were beautiful at interactive work—multiple users, multitasking, clean interfaces. But they couldn't do what proprietary mainframe systems like IBM's JES could do brilliantly: sophisticated batch processing. When you needed to submit hundreds of computational jobs and have them execute across multiple machines based on resource availability and priority, Unix just... couldn't.²

NASA Ames Research Center needed to manage the computational resources of their Cray-2 and Cray Y-MP supercomputers. Brent Kingsbury of Sterling Software created NQS in May 1986 to solve this problem. It was released as a portable Unix application—you could run it on any Unix system and suddenly have the batch processing capabilities that previously required proprietary systems.³

The timing was perfect. Unix was spreading through universities and research institutions, all facing the same problem. NASA put NQS into the public domain to encourage adoption. Hardware vendors immediately grabbed it, ported it to their platforms, and started building on it.

Why It Mattered

In 1987, when POSIX needed to standardize batch processing for Unix systems, they chose NQS as the model. Not because it was the only option, but because it was public domain, already implemented on multiple hardware platforms, network-based, and widely accepted by both vendors and users.⁴

NQS became the foundation. The Portable Batch System (PBS)—still widely used today—was developed in the early 1990s as an enhancement to NQS.⁵ Modern schedulers like LSF included NQS interoperation features.⁶ The ideas pioneered in NQS—network-based job routing, queue management, resource allocation—are fundamental to how we run computational work today.

Current Status

You won't find much NQS traffic on port 607 anymore. The protocol has been superseded by PBS, SLURM, and other modern schedulers that use different ports and protocols. But the port remains officially assigned to NQS in IANA's registry, a quiet reminder of where batch scheduling on Unix began.

Some sources note that port 607 has been observed in unofficial uses, and like many older assigned ports, malware has occasionally abused it for communication. But these are opportunistic uses of an available port number, not the original NQS service.

How to Check What's Using Port 607

On Linux or macOS:

# See what's listening on port 607
sudo lsof -i :607

# Or using netstat
sudo netstat -tlnp | grep :607

On Windows:

netstat -ano | findstr :607

If you see something listening on port 607 in a modern environment, it's worth investigating—it's almost certainly not NQS.

Why Unassigned Ports Matter

Port 607 isn't truly unassigned—it has an official assignment to NQS. But it's functionally unused in modern networks, which makes it similar to unassigned ports in practice.

The well-known range (0-1023) contains many such ports: services that mattered deeply in their time but have been replaced by newer protocols. These ports tell the history of the Internet. They're markers of problems we once had and solutions that worked well enough to become standards.

Every modern job scheduler—every time you submit work to a computing cluster, every CI/CD pipeline that queues builds, every cloud service that manages batch workloads—carries a little DNA from NQS. Port 607 is where that story started.

Related Ports

• Port 111 — Portmapper/rpcbind, another service from Unix's network computing era
• Port 512-514 — BSD r-commands (rexec, rlogin, rsh), remote execution from the same era
• Registered/Dynamic Ports — Modern schedulers like PBS and SLURM use ports in the registered range (1024-49151)