[pulseaudio-discuss] pulseaudio

[Sean McNamara]

Hi,

On Tue, Apr 12, 2011 at 12:15 PM, duportail <poort at telenet.be> wrote:
> Try to test the new xubuntu 11.04 with kde on a multi-user system.
> The first user (for example user1) can log in and gets a default sink from
> pulse.
> The second user(for example user2) that will log in gets a auto_null because
> pulse did not found any sinks.
> If i log out user1, than user2 can get a default sink by kill and start
> pulse.
> Where should be the reason?

This is the "classic" multi-user problem: you're using a soundcard
without hardware mixing, so only one ALSA application can take direct
control of the hardware device at a time. user1's pulseaudio daemon
takes control of it, so obviously user2's PA daemon will just get
"Device or resource busy" when trying to snd_pcm_open() on hw:0 (for
example). This problem has existed since ALSA existed. There's no
direct fix without scrapping the API and rewriting it.

I guess there is no solution yet (still) in 11.04, but you can see
that folks in the Ubuntu community are trying to resolve the issue
with a number of possible approaches:
https://wiki.edubuntu.org/BluePrints/multiuser-soundcards-pulseaudio

Running as system-wide is one possible approach...
http://www.pulseaudio.org/wiki/SystemWideInstance

Not sure if there's yet a solution allowing the use of shm and
module-native-protocol-unix for multiple users (this is ideally what
you'd want for maximum performance / minimum latency), but it's quite
easy to set up module-native-protocol-tcp and connect to localhost
using the `default-server' parameter in client.conf, at the cost of
latency. Let me know if you need more details on this particular
approach.

BTW, search the archives of this list at gmane <
http://blog.gmane.org/gmane.comp.audio.pulseaudio.general > -- there
are many many historical posts about multi-user setups.



Sean

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