[pulseaudio-discuss] pulseaudio problem when using x2go and likewise-open

Colin Guthrie gmane at colin.guthr.ie
Wed Dec 15 06:22:02 PST 2010

'Twas brillig, and Ivan Boyadzhiev at 15/12/10 09:48 did gyre and gimble:
> Hi,
> I have read all the related documentation on
> http://www.pulseaudio.org/wiki/ServerStrings and related wikis, and I
> understood what it is written there, still I need some more information
> how can I debug or start manually pulseaudio SSH forward.
> What is this thread about: Ubuntu 10.10 with Likewise-open connected to
> corporate LDAP. X2go server installed and configured using pulseaudio
> forwarding sound from the server to the clients. Problem: x2goclient
> can't make ssh pulseaudio tunnel when using LDAP user. x2goclient can
> make ssh pulseaudio tunnel when using local ubuntu user.
> It is nothing with group permissions, as they are not needed, because I
> do have configured, and working system wide mode
> (http://www.pulseaudio.org/wiki/SystemWideInstance). Logging physically
> on the Ubuntu x2goserver with LDAP user does have sound, but the access
> to the soundcard is through the physical hardware.

I'm really sorry but I really can't understand what you are trying to
achieve. The above is quite convoluted, so perhaps you could try to
explain in a clearer way what you are actually trying to do and we can
advise better.

LDAP is really irrelevant here. Also there are no such things as SSH
tunnels for PA in terms of what "just happens". SSH only knows how to
forward X11 protocol, and we piggy back on to that for *configuration*
only, not actual transport.

When a PA client runs, it looks at the properties on the X11 root window
(xprop -root | grep PULSE) in order to get the PULSE_COOKIE and
PULSE_SERVER strings. The cookie is obviously used for authentication
and the server string tells libpulse where to try and connect to PA. In
a remote situation this will ultimately require a TCP connection. Due to
this you need to ensure you are able to establish a connection back to
the source machine directly on TCP port 4713.

If this works then all is well.

You have to enable networking support on the source (ie. client)
machine. It can be enabled via paprefs.

> I am in touch with x2go-developers, and there have live discussion with
> them on their mailing list as well:
> https://lists.berlios.de/pipermail/x2go-dev/2010-December/thread.html#start
> and more specific: the thread: [X2go-dev] x2go with likewise-open (ldap)
> questions
> <https://lists.berlios.de/pipermail/x2go-dev/2010-December/001361.html>
> Currently I do have 2 remote open x2go sessions. One using LDAP user,
> the other Local Ubuntu user. I don't have anything in hardware and aplay
> -l or aplay -L or lspci -v are absolutely same. The difference from
> gnome-volume-control is the Output Tab. The LDAP user has Dummy Output,
> while the Local Ubuntu user has Windows waveOut PCM
> My questions are:
>  1. In this situation, can I try to start manually pulseaudio server
> forward in the LDAP user?

LDAP is irrelevant. If you are using system-wide PA then perhaps it was
started before LDAP support etc. and thus cannot check the groups users
are in?

>  2. Is there a way do make some deep debugs on the LDAP user, so to get
> what exactly is getting wrong

I'm still not really sure what topology you describe, where the client
machines are and where the the x2go sessions should be connecting to.

I'd be more than happy to discuss things with and advise how best to
achieve the end goal, but it's like something that would be better done
on IRC a little more interactively.

> P.S. My assumption is that x2go side has un-escaped string for username,
> which now because of LDAP include "@" and converted to "\". I'm checking
> the sources, still that will take its time.
> My x2goclients are both Windows 7(for all my experience up is used), and
> another Ubuntu 10.10 (on VMware). The VM has sound, but the x2goclient
> does not have in all cases (doesn't matter if the user is LDAP or Local
> Ubuntu).
> Bottom line: can you give me more information how this forward happens
> exactly, or help me with deep investigation from pulseaudio side.

As I said above, we do not do any forward at all (well, it would be SSH
that does this if anything, but it doesn't - yet). All we do is piggy
back onto X11 forwarding built in to SSH.

Overall, I'm not sure where you are running PA and why it needs to be
system-wide at all (generally I would not recommend this), but come on
IRC and then we can discuss and I can explain how things should be
setup. I'm coling in #pulseaudio on Freenode.

FWIW, I describe how the Remote X11 case works here:

which may be useful reading.



Colin Guthrie

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