D-Bus

D-Bus is a message bus system that provides a mechanism for inter-process communication.

Some services rely on a D-Bus session instance or expect it by default (including Pipewire). Other processes will only be able to communicate with these services if d-bus is running.

You can start a dbus session like this: dbus-run-session -- sh(replacing sh with your shell or a window manager), or, export $(dbus-launch). This is distinct from running dbus system-wide: rc-service dbus start, which is a prerequisite to run a user dbus session.

D-Bus passes the environment variable $DBUS_SESSION_BUS_ADDRESS to its children. Running dbus-launch in a terminal means that other running process won't find this D-Bus's socket.

If $DBUS_SESSION_BUS_ADDRESS is undefined, many applications will attempt to use the standard path:

$XDG_RUNTIME_DIR/bus

Running D-Bus like so should work for many applications:

dbus-daemon --nofork --address unix:path=$XDG_RUNTIME_DIR/bus --session

For applications that dont work without $DBUS_SESSION_BUS_ADDRESS you can prepend your program with the follow workaround script which avoid launching multiple user dbus sessions:

#!/bin/sh
if [ ! -e "/tmp/dbus-$USER-env" ]; then
       echo "Creating new dbus session on /tmp/dbus-$USER-env"
       export $(dbus-launch)
       echo "${DBUS_SESSION_BUS_ADDRESS}" > /tmp/dbus-$USER-env
       echo "Dbus session address is: ${DBUS_SESSION_BUS_ADDRESS}"
else
       echo "Using dbus session address from /tmp/dbus-$USER-env"
       export DBUS_SESSION_BUS_ADDRESS="$(cat /tmp/dbus-$USER-env)"
       echo "Dbus session address is: ${DBUS_SESSION_BUS_ADDRESS}"
fi
if [ -n "$1" ]; then
       $@
fi

See also

• Pipewire and D-Bus
• Archwiki
• Gentoo Wiki