The Linux Process Journey — dbus-monitor (Debug Probe to Print Message Bus Messages)
dbus-monitor (Debug Probe to Print Message Bus Messages) is an ELF binary located at “/usr/bin/dbus-monitor” and\or “/bin/dbus-monitor”. It intercepts and displays real-time traffic on a D-Bus (https://medium.com/@boutnaru/the-linux-concept-journey-d-bus-desktop-bus-dd8c69ade019) message bus. Use the “ — system” or “ — session” flags to target the system-wide service or the per-user bus (the default), and filter specific events by appending watch expressions (https://linux.die.net/man/1/dbus-monitor).
Overall, while it defaults to a verbose “classic” output the “ — profile” flag enables a compact single line format (with microsecond precision for performance analysis). It is important to understand that advanced debugging may require root privileges. This is due to the fact bus security policies often restrict non-privileged users from eavesdropping on all messages (https://dbus.freedesktop.org/doc/dbus-monitor.1.html).
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Lastly, “dbus-monitor” functions by registering “match rules” with the bus daemon to explicitly request eavesdropping privileges (allowing it to see messages intended for other applications). Once connected, it enters a continuous event loop that intercepts incoming signals\method calls\errors. Hence, routing them through one of two filters: a human readable monitor mode for debugging or a timestamped profile mode for performance analysis (https://github.com/brianmcgillion/DBus/blob/master/tools/dbus-monitor.c). “dbus-monitor” is part of the “dbus-bin” package (https://packages.debian.org/sid/dbus-bin).
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