What is the meaning of 'sender=:1.478' in dbus-monitor?

Question

Nowadays I am analyzing d-bus in Chromium OS (Chrome OS).
I captured meaningful d-bus method calls (below), when I press ''guest' button on login UI.

my-cros # dbus-monitor --system "path=/org/chromium/Session Manager"

method call time=1632311881.319994 sender=: 1.478 -> destination=org.chromium. SessionManager serial=378 path=/org/chromium/Session Manager; interface=org.chromium.SessionManager Interface: member=LoadShil1Profile 
string "$guest"

method call time=1632311881.319417 sender:1.478 -> destination=org. chromium. Session Manager serial=371 path=/org/chromium/SessionManager; interface=org.chromium.SessionManager Interface: member-SetFeatureFlagsFor User string "$guest"
array [
]
array [
]

I know that org.chromium.SessionManager is the one who starts guest/google-id session.
Btw what is the meaning of 'sender=:1.478'?
And how to track the sender process?

Thank you in advance.

Answer 1

Firstly, you might find it easier to visualise what’s going on by using Bustle instead of dbus-monitor.

sender=:1.478 means the message you’re looking at was sent by the connection with unique ID :1.478 on the bus. Each connection to the bus (roughly, each process, although a process can actually have more than one connection) has a unique ID, and some connections also have ‘well-known’ IDs which look like reverse-DNS names. For example org.chromium.SessionManager.

You can track the sender process by looking for the same unique ID appearing as the sender or destination of other messages. Using Bustle will make this easier, as it can group and filter messages by sender/destination.