How do I debug issues with Pulse Audio?

This preliminary answer summarizes steps involved to debug sound available for one user only in an environment where domains were joined for this user. It may need be extended later.

In case we have sound for one user only we may have some bad configuration in this one user account's setting. We need to take the following steps from the affected user account to get further insights into the problem.

1. Is pulseaudio running at all?
   Usually you will see that from having access to the sound menu in the top bar. Alternatively we can issue the following command in a terminal:

   pulseaudio -k
   

   There will be an error in case pulseaudio does not run. In addition this command takes care of stopping and respawning pulseaudio in case it hangs.

2. Are there wrong user settings for the pulseaudio daemon?
   To test this we have to rename the settings directory in the affected user's HOME followed by a restart of pulseaudio (see 1.):

   mv ~/.pulse ~/.pulse.bad
   

   or

   mv ~/.config/pulse ~/.config/pulse.bad  ## for newer releases
   

3. Are channels muted from ALSA?
   We may open the alsamixer in a terminal to adjust channel volumes, and to unmute a channel in case it was accidentally muted:

   alsamixer
   

4. Make sure users are not in the 'audio' group
   A user in the audio group has exclusive access to the pulseaudio server. Other users can not access it while this user uses it. Therefore user should not be in the audio group.

5. Start Pulseaudio manually
   In case pulseaudio was not running we can also start the daemon from command line with

   pulseaudio -D
   

   Pulseaudio then uses default settings and starts it's daemon. We can also put this command to our Autostart Applications to overcome the case when pulseaudio fails to run before the desktop was loaded.

6. Browse log files
   Pulseaudio will be loaded on system start up, and on user login. Therefore errors can only be read from a log generating on starting pulseaudio. See this guide on how to generate a pulsaudio log script. In short, we have to take care pulseaudio does not respawn we may run it in verbose mode:

   pulseaudio -vvvv <options>
   

_{to be completed}

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In the case given in the question we could see that pulseaudio fails to run because it was unable to start the D-Bus service. This may likely be caused by a broken or overlong path to the user's HOME (see bug #872992). As a workaround we may issue pulseaudio without D-Bus control by commenting out the following line in /etc/pulse/default.pa like this:

# load-module module-dbus-protocol

However then we (and our applications) will not be able to control pulseaudio using D-Bus.

on my Debian system, I was able to get this working after, on the advice of someone smarter than me, copying (as root) the $HOME/.pulse/ folder and $HOME/.pulse-cookie files from $USER_A to $USER_B, chowning them appropriately.