# systemd adds Varlink traffic monitoring with varlinkctl monitor

> **Key takeaway:** systemd now includes a varlinkctl monitor command and an io.systemd.VarlinkMonitor service for capturing and filtering Varlink traffic, analogous to dbus-monitor for D-Bus.

**Published:** 2026-10-18T13:37:00+00:00 
**Source:** Planet freedesktop.org 
**Category:** distro-planet 
**Canonical URL:** https://fosswire.org/news/systemd-adds-varlink-traffic-monitoring-with-varlinkctl-moni.html 

## Summary
systemd has gained new observability tools for Varlink, the protocol increasingly used alongside D-Bus in modern Linux systems. A new io.systemd.VarlinkMonitor service provides a ring buffer for filtered traffic capture, while the varlinkctl monitor command exposes this functionality for terminal and script use. Output can be formatted as JSON-seq for processing with jq. The tooling was presented at All Systems Go; the author suggests future integration with Bustle for unified D-Bus and Varlink system-wide visibility.

## What the new Varlink monitoring tools provide
- **io.systemd.VarlinkMonitor**: new Varlink service that maintains a ring buffer of captured packets matching user-supplied filters
- **varlinkctl monitor**: new CLI verb exposing the service for interactive and scripted use; equivalent to dbus-monitor for the Varlink protocol
- **--json short flag**: emits JSON-seq output, compatible with `jq --seq` for structured processing
- **Current gap**: no equivalent to Bustle's graphical D-Bus capture; unified D-Bus/Varlink visualization not yet available

## Why it matters
As systemd components and other system services migrate from D-Bus to Varlink, administrators and developers lose the mature observability tooling built around D-Bus. These tools begin to close that gap, though unified visibility across both protocols remains a future goal.