Connecting to dbus over tcp

Question

I wrote a simple python program to play and pause banshee music player. While its working on my own machine, I have trouble doing it to a remote computer, connected to the same router (LAN). I edited the session.conf of the remote machine, to add this line:

<listen>tcp:host=localhost,port=12434</listen>

and here is my program:

    import dbus


    bus_obj=dbus.bus.BusConnection("tcp:host=localhost,port=12434")
    proxy_object=bus_obj.get_object('org.bansheeproject.Banshee',                              
    '/org/bansheeproject/Banshee/PlayerEngine')

    playerengine_iface=dbus.Interface(proxy_object,
    dbus_interface='org.bansheeproject.Banshee.PlayerEngine')

    var=0

    while (var!="3"):
        var=raw_input("\nPress\n1 to play\n2 to pause\n3 to exit\n")


            if var=="1":
                print "playing..."
                playerengine_iface.Play()

            elif var=="2":
                print "pausing"
                playerengine_iface.Pause()

This is what i get when i try to execute it

Traceback (most recent call last):
  File "dbus3.py", line 4, in <module>
    bus_obj=dbus.bus.BusConnection("tcp:host=localhost,port=12434")
  File "/usr/lib/python2.7/dist-packages/dbus/bus.py", line 125, in __new__
    bus = cls._new_for_bus(address_or_type, mainloop=mainloop)
dbus.exceptions.DBusException: org.freedesktop.DBus.Error.NoServer: Failed to connect to socket "localhost:12434" Connection refused

What am I doing wrong here? should i edit /usr/lib/python2.7/dist-packages/dbus/bus.py

UPDATE:

ok, here is the deal when i add

<listen>tcp:host=192.168.1.7,port=12434</listen>

to to /etc/dbus-1/session.conf, then reboot, hoping it would start listening on reboot, It never boots. It gets stuck on loading screen and occasionally, a black screen with the following text flashes:

Pulseaudio Configured For Per-user Sessions Saned Disabled;edit/etc/default/saned

so, when i go ctrl+alt+f1 , change session.conf to original state and reboot, it boots properly.

Whats all that about? How can I make dbus daemon listen for tcp connections, without encountering problems?

Answer 1

I recently needed to set this up, and discovered that the trick is: order matters for the <listen> elements in session.conf. You should make sure the TCP element occurs first. Bizarre, I know, but true, at least for my case. (I see exactly the same black screen behavior if I reverse the order and put the UNIX socket <listen> element first.)

Also, prepending the TCP <listen> tag is necessary, but not sufficient. To make remote D-Bus connections via TCP work, you need to do three things:

1. Add a <listen> tag above the UNIX one, similar to this:

   <listen>tcp:host=localhost,bind=*,port=55556,family=ipv4</listen>
   <listen>unix:tmpdir=/tmp</listen>
   

2. Add a line (right below the <listen> tags is fine) that says:

   <auth>ANONYMOUS</auth>
   

3. Add another line below these that says:

   <allow_anonymous/>
   

The <auth> tag should be added in addition to any other <auth> tags that may be contained in your session.conf. In summary, your session.conf should contain a snippet that looks like this:

<listen>tcp:host=localhost,bind=*,port=55556,family=ipv4</listen>
<listen>unix:tmpdir=/tmp</listen>

<auth>ANONYMOUS</auth>
<allow_anonymous/>

After doing these three things, you should be able to connect to the session bus remotely. Here's how it looks when specifying a remote connection in D-Feet:

Note that, if you want to connect to the system bus, too, you need to make similar changes to /etc/dbus-1/system.conf, but specify a different TCP port, for example 55557. (Oddly enough, the element order appears not to matter in this case.)

The only weird behavior I've noticed in this configuration is that running Desktop apps with sudo (e.g., sudo gvim) tends to generate errors or fail outright saying "No D-BUS daemon running". But this is something I need to do so rarely that it hardly matters.

If you want to send to a remote machine using dbus-send, you need to set DBUS_SESSION_BUS_ADDRESS accordingly, e.g., to something like:

export DBUS_SESSION_BUS_ADDRESS=tcp:host=localhost,bind=*,port=55556,family=ipv4

This works even if the bus you want to send to is actually the system bus of the remote machine, as long as the setting matches the TCP <listen> tag in /etc/dbus-1/system.conf on the target. (Thanks to Martin Vidner for this tip. Until I stumbled across his answer to this question, I didn't believe dbus-send supported remote operation.)

UPDATE: If you're using systemd (and want to access the system bus), you might also need to add a line saying ListenStream=55557 to /lib/systemd/system/dbus.socket, like so:

[Socket]
ListenStream=/var/run/dbus/system_bus_socket
ListenStream=55557  # <-- Add this line

UPDATE2: Thanks to @altagir for pointing out that recent versions of D-Bus will enable AppArmor mediation on systems where it's available, so you may also need to add <apparmor mode="disabled"/> to session.conf/system.conf for these instructions to work.

Answer 2

since dbus 1.6.12 (e.g. kubuntu 13.10), your connection will also be rejected unless you add to your dbus config file (either /etc/dbus-1/mybus.conf or the interface requiring remote access i.e. system.d/my.interface.conf)

<apparmor mode="disabled"/>

UPDATE: After struggling to create a apparmor profile allowing the service to connect to the custom dbus-daemon, it seems the connection is always rejected due to a bug in DBUS... So for now we MUST disable apparmor whenever you use tcp=... Bug fix targetted for 14.04

I opened a bug at bugs.launchpad.net following discussion here with Tyler Hicks:

The AppArmor mediation code only has the ability to check peer labels over UNIX domain sockets. It is most likely seeing an error when getting the label and then refusing the connection.

Note: the disable flag is not recognized by dbus < 1.6.12, so you need to package different versions of mydaemon.conf depending on systen), else dbus-daemon will fail on launch if no apparmor... I used for now in my CMakeLists.txt :

IF(EXISTS "/usr/sbin/apparmor_status")
  install(FILES dbus_daemon-apparmordisabled.conf RENAME dbus_daemon.conf DESTINATION /etc/dbus-1/ )
ELSE (EXISTS "/usr/sbin/apparmor_status")
   install(FILES dbus_daemon.conf DESTINATION /etc/dbus-1/ )
ENDIF(EXISTS "/usr/sbin/apparmor_status")

Answer 3

Another thanks @Shorin, and another FYI - I had to do something like this to make mine work:

<listen>tcp:host=localhost,bind=0.0.0.0,port=55884</listen>

Note the bind=0.0.0.0 - the bind=* didn't work for me, and I left out the family=ipv4 part. I'm on Ubuntu 12.04. I did use netstat on the remote machine to confirm dbus was listening on the port and telnet from local to confirm the port was open.

netstat -plntu | grep 55884

tcp   0     0 0.0.0.0:55884    0.0.0.0:*     LISTEN    707/dbus-daemon

You have to see something like 0 0.0.0.0:55884 and not something like 0 127.0.0.1:55884.