Audio redirection won't work if PulseAudio is started by per-user systemd

[metalefty]

xrdp uses the following environment variables to pass the locations of audio socket files and socket files directory between xrdp session and PulseAudio module. See also https://github.com/neutrinolabs/pulseaudio-module-xrdp/search?q=getenv&type=code.

• XRDP_SOCKET_PATH
• XRDP_PULSE_SINK_SOCKET
• XRDP_PULSE_SOURCE_SOCKET
• PULSE_SCRIPT

However, recent GNU/Linux systems use systemd to start the per-user PulseAudio process. Not a child process of xrdp-sesman. For example, /etc/systemd/user/default.target.wants/pulseaudio.service is the target to start PulseAudio process.

This is an example of the environment variables pulseaudio process started from systems can see. Necessary environment variables are not visible from systems pulseaudio. As a result, unfortunately, audio redirection does not work.

DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
HOME=/home/meta
LANG=ja_JP.UTF-8
LOGNAME=meta
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin
SHELL=/bin/bash
USER=meta
XDG_DATA_DIRS=/home/meta/.local/share/flatpak/exports/share:/var/lib/flatpak/exports/share:/usr/local/share:/usr/share
XDG_RUNTIME_DIR=/run/user/1000
NOTIFY_SOCKET=/run/user/1000/systemd/notify
MANAGERPID=115733
LISTEN_PID=115755
LISTEN_FDS=1
LISTEN_FDNAMES=pulseaudio.socket
INVOCATION_ID=85269c9159824369b61b068cb1cb4dab
JOURNAL_STREAM=9:1508197

We need to consider how to pass some necessary information from xrdp to the PulseAudio module.

This issue is originally reported by @CyberTrust and @haw.

[matt335672]

I had a brief Gitter conversation about this with @derekschrock back in October last year. At the time we managed to get something working by running the xrdp session with a separate dbus instance. At the time this wasn't possible with Gnome due to its heavy dependence on systemd --user, and I suspect over time it will become harder for other desktop environments too.

Something I was playing with was making the environment variables to the modules parameters instead. Then the PULSE_SCRIPT can use pactl to load the modules dynamically into the systemd --user instance of pulseaudio. I only had a brief play with it, and didn't get it working. However, the code is here:-

https://github.com/matt335672/pulseaudio-module-xrdp/tree/module_params

I've not considered unloading the modules when the session ends yet, or anything like that.

[abma]

i've created a login script which loads dynamicly the xrdp-pulse modules:

  pactl load-module module-xrdp-sink
  pactl load-module module-xrdp-source

this way the systemd-stuff doesn't need to be touched and sound works inside the xrdp session!

[matt335672]

Hi @abma

That's really interesting - thanks.

The modules use environment variables to locate the chansrv endpoints. If these are readable by the pulse audio server, this should work.

In your instance, what is the output of systemctl --user show-environment? Did you need to use any systemctl --user set-environment variables to get this working?

[abma]

$ systemctl --user show-environment
[...]
XRDP_PULSE_SINK_SOCKET=xrdp_chansrv_audio_out_socket_11
XRDP_PULSE_SOURCE_SOCKET=xrdp_chansrv_audio_in_socket_11
XRDP_SESSION=1
XRDP_SOCKET_PATH=/run/xrdp/sockdir

Did you need to use any systemctl --user set-environment variables to get this working?
no!

i basicly just created the file /etc/X11/Xsession.d/99xrdp-pulse:

pactl load-module module-xrdp-sink
pactl load-module module-xrdp-source

(its sourced, no +x / shebang required)

[matt335672]

Thanks for the additional info.

On Ubuntu, the following command in /etc/X11/Xsession.d/95dbus_update-activation-env seems to be doing all the magic for us:-

dbus-update-activation-environment --verbose --systemd --all

Provided your login script runs after this line, you should be fine.

Currently xrdp is set up to provide the environment "PULSE_SCRIPT" for use by the PulseAudio daemon. That method doesn't work for systemd-based systems, as pulseaudio is started when the PAM session is started (which is before the windows session runs).

I created the following script on my system under /etc/X11/Xsession.d/90xrdp-pulse. Permissions are 644.

# This file is sourced by Xsession(5), not executed.

if [ -n "$XRDP_SESSION" -a \
     -n "$DISPLAY" -a \
     -n "$XRDP_SOCKET_PATH" -a \
     -n "$XRDP_PULSE_SINK_SOCKET" -a \
     -n "$XRDP_PULSE_SOURCE_SOCKET" ]
then
     if systemctl --user is-active pulseaudio >/dev/null 2>&1
     then
         systemctl --user set-environment \
             DISPLAY="$DISPLAY" \
             XRDP_SOCKET_PATH="$XRDP_SOCKET_PATH" \
             XRDP_PULSE_SINK_SOCKET="$XRDP_PULSE_SINK_SOCKET" \
             XRDP_PULSE_SOURCE_SOCKET="$XRDP_PULSE_SOURCE_SOCKET"
        pactl load-module module-xrdp-sink
        pactl load-module module-xrdp-source
    fi
fi

This doesn't depend on dbus-update-activation-environment being called, and also won't try to load xrdp drivers for non-xrdp sessions. It seems to work on Ubuntu 20.04, apart from some latency issues which I haven't looked at yet.

Any chance you could try that on your system? If it's OK there, we can add it to the wiki.

[abma]

sadly the "pactl load-module" way didn't work stable for me. sometimes i had sound, sometimes not. the pulseaudio service and/or process sometimes seems to stay running after logout.

i've reported it upstream, maybe they have an idea: https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/issues/1271

[matt335672]

Well, thanks for looking at at it and reporting back.

[matt335672]

@abma - please take a look at neutrinolabs/pulseaudio-module-xrdp#59 which will (I think) sort everything out for you. Feel free to build it from my repo directly:-

git clone https://github.com/matt335672/pulseaudio-module-xrdp.git
cd pulseaudio-module-xrdp
git checkout module_params

[abma]

in a quick test i noticed it seems more reliable: i have sound instantly, without the patch it needed ~10 seconds until sound started.

for now i just updated the modules: when it works nice (on a server with ~50 users) i will try again starting it via systemd.

thanks!

[matt335672]

pulseaudio-module-xrdp 0.6 has been released which now supports pulseaudio being started by per-user systemd.