Port 3112: KDE System Guard — Remote monitoring for Linux desktops

What Port 3112 Does

Port 3112 is registered with IANA for ksysguardd, the daemon component of KDE System Guard. ¹

KDE System Guard was a task manager and performance monitor for the KDE desktop environment on Linux and other Unix-like systems. It had two parts: the GUI you interacted with, and a daemon (ksysguardd) that could run on remote machines. When you wanted to monitor a remote host, the GUI connected to the remote daemon over TCP on port 3112. From there, you could watch that machine's CPU, memory, disk activity, and running processes as if it were local. ²

It was a clean idea: a lightweight daemon speaking a simple text protocol, a graphical front-end connecting wherever you pointed it. For Linux system administrators in the early-to-mid 2000s who lived in the KDE desktop, it was a useful tool.

The Protocol

The ksysguard protocol was deliberately simple — a line-based text protocol over TCP. The daemon would respond to queries with sensor readings. You could connect with a plain terminal and talk to it. No binary framing, no complex handshaking. Just text in, readings out. ³

This simplicity was both its strength and its limitation.

Current Status

ksysguard has been deprecated. KDE replaced it with Plasma System Monitor, which uses a different architecture and does not rely on the ksysguardd daemon or port 3112. ⁴

The IANA registration for port 3112 remains, but the software that used it is largely gone from active distributions.

Other Observed Uses

Snom IP phones used port 3112 for a legacy HTTP web interface that allowed configuration and remote control via simple URL-based commands. Starting with firmware version 10.1.159.12, Snom moved the web interface to HTTPS-only and began deprecating the old interface. The port 3112 web UI can still be re-enabled via configuration, but it is considered legacy. ⁵

Port 3112 also falls within the UDP range 3074-3174 used by Rainbow Six Vegas for online multiplayer, though this is incidental rather than specific to this port number. ⁶

What Range This Port Belongs To

Port 3112 is a registered port (range 1024-49151). ¹

Registered ports are different from well-known ports (0-1023), which are reserved for foundational Internet services like HTTP, SSH, and DNS. In the registered range, organizations and projects can apply to IANA for an official assignment. This is how ksysguard ended up here — someone from the KDE project filed for it.

A registered assignment does not mean the port is widely used, actively maintained, or that you will encounter it in the wild. It means that at some point, someone asked for it and IANA said yes.

How to Check What Is Listening on This Port

If you see traffic on port 3112 and want to know what is using it:

On Linux or macOS:

# Show what process is listening on port 3112
ss -tlnp | grep 3112

# Or with lsof
lsof -i :3112

On Windows:

netstat -ano | findstr :3112

On any system, to probe a remote host:

# Check if port 3112 is open on a remote machine
nc -zv hostname 3112

# Or with nmap
nmap -p 3112 hostname

If you see something listening on this port today, it is unlikely to be ksysguardd. More probable candidates: a Snom phone's legacy web interface, a game, or application-specific traffic that chose this port because it happened to be free.

Why Unassigned (or Retired) Ports Matter

Port 3112 illustrates something real about the port system: registrations outlive software. The IANA assignment stays in the registry long after the daemon stops shipping in distributions. The number becomes a kind of historical marker — evidence that a piece of software existed, had network ambitions, and eventually was superseded.

The 48,000+ ports in the registered range are filled with these quiet histories. Most see no traffic. Some were ambitious. A few are now security concerns, because old software still runs in forgotten corners, listening on ports that nobody monitors.