Looks like Ubuntu Saucy needs XDG_RUNTIME_DIR (see http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html) set. This is part of the normal user session setup and needs to be duplicated manually when starting a custom D-Bus session. For now, you can do: export XDG_RUNTIME_DIR=`mktemp -d` before invoking dbus-session.sh. The directory can be removed when the session ends. Eventually I'll probably have to add that to dbus-session.sh. I wonder whether that explains some of the random problems that I have seen with parallel testing on Saucy and Ubuntu: multiple different D-Bus sessions probably ended up using the same /run/user dir.