Pulseaudio for multi-user breaks jack & alsa_seq/midi usage

salinas_v · 2012-03-18 01:15:01

Hi, I have been trying to figure out for some time now and I can't find a solution.

I have used pulse+jack for some time but now I share my desktop and found that pulse doesn't play nice with multi-user if they are part of the audio group [1] (intuitive right?)

So I have deleted both of us from the audio group but now I can't get the alsa sequencer to connect my midi controller to fluidsynth because I don't have the permissions. /dev/snd/seq is owned by root and audio group.

How can I get pulse working with multi-user without breaking my ability to play with midi?

Is uninstalling pulse my best bet?

PS:Btw, before, while being part of audio group I was able to use the midi controller just OK.

[1] http://www.freedesktop.org/wiki/Softwar … rfectSetup

ngoonee · 2012-03-18 09:46:10

How do you 'use pulse and jack'? A bit more of a description on what you have set up might help. Based on the information you've provided though I'd say you may be better of not using pulse unless there's something it does that you require. Running pulse ON TOP of Jack is another possibility.

salinas_v · 2012-03-18 22:19:29

Sure

I do use jack2 so once I run anything that needs jack, it ask pulse to stop, give the hw resources to jack and run pulse on top of it. As single user, this work just ok.

My desktop have two users, the second user (not me) primary usage of the desktop is actually listening to music in the audio setup I have here (amplifiera, speakers and stuff).

Originally I had both users in the audio group because I wanted both of us to have access to audio features (like playing audio) but if I'm logged in, the second user can't hear anything. Looking for more information to be able to fix this issue I found that Pulseaudio doesn't like to have users in the audio group. So, I deleted both of us from the group.

Now, Pulse works ok but the problem is that alsa needs me to be in the audio group to access the /dev/snd/seq which is used by my M-audio midi controller. This midi controller is loaded as an alsa midi device (I haven't figured out where by who or how to change it to be loaded as jack midi device), but since I'm not in the audio group,I can't see it anymore.

I tried running a2j but I get this error:

[0]salinasv@aquelarre ~ $ a2jmidid -e &
[1] 10993
[0]salinasv@aquelarre ~ $ JACK MIDI <-> ALSA sequencer MIDI bridge, version 7 (b169fb6b8e9e11ce1488d1964649aabedbb89ddf) built on Wed Dec 31 18:00:00 1969
Copyright 2006,2007 Dmitry S. Baikov
Copyright 2007,2008,2009,2011 Nedko Arnaudov

Bridge starting...
Using JACK server 'default'
Hardware ports will be exported.
ALSA lib seq_hw.c:457:(snd_seq_hw_open) open /dev/snd/seq failed: Permission denied
ERROR: a2j_new: failed to open alsa seq
ERROR: a2j_start: a2j_new() failed.

[1]+  Done                    a2jmidid -e

This is the ls -la of /dev/snd/seq and it explains why I have no permissions to use the device.

[0]salinasv@aquelarre ~ $ ls -al /dev/snd/seq 
crw-rw---- 1 root audio 116, 1 Mar 13 22:07 /dev/snd/seq

Am I missing something? It is possible to use alsa sequencer without being in the audio group? Does Pulse just don't play well with anything else? Sould I just uninstall pulse?

salinas_v · 2012-03-18 22:34:44

I have just noticed that /dev/snd/seq is the only one that doesn't have the + sign at the end of the permission field. This means that *only* this one doesn't have the extended permissions and it is not controlled by ACL. Are this ACL stuff needed to work

[0]salinasv@aquelarre ~ $ ls -l /dev/snd
total 0
drwxr-xr-x  2 root root       60 Mar 18 01:01 by-id/
drwxr-xr-x  2 root root      100 Mar 18 01:01 by-path/
crw-rw----+ 1 root audio 116,  7 Mar 13 22:07 controlC0
crw-rw----+ 1 root audio 116,  9 Mar 13 22:07 controlC1
crw-rw----+ 1 root audio 116, 12 Mar 13 22:07 controlC2
crw-rw----+ 1 root audio 116,  6 Mar 13 22:07 hwC0D0
crw-rw----+ 1 root audio 116, 11 Mar 13 22:07 hwC2D0
crw-rw----+ 1 root audio 116,  8 Mar 13 22:07 midiC1D0
crw-rw----+ 1 root audio 116,  5 Mar 13 22:10 pcmC0D0c
crw-rw----+ 1 root audio 116,  4 Mar 13 22:10 pcmC0D0p
crw-rw----+ 1 root audio 116,  3 Mar 13 22:09 pcmC0D1p
crw-rw----+ 1 root audio 116,  2 Mar 13 22:07 pcmC0D2c
crw-rw----+ 1 root audio 116, 10 Mar 13 22:09 pcmC2D3p
crw-rw----  1 root audio 116,  1 Mar 13 22:07 seq
crw-rw----+ 1 root audio 116, 33 Mar 13 22:07 timer

I just ran getfacl on one file with the + sign and the seq one and it looks like seq is missing my user as "user"

[0]salinasv@aquelarre ~ $ getfacl /dev/snd/pcmC0D0c
getfacl: Removing leading '/' from absolute path names
# file: dev/snd/pcmC0D0c
# owner: root
# group: audio
user::rw-
user:salinasv:rw-
group::rw-
mask::rw-
other::---

[0]salinasv@aquelarre ~ $ getfacl /dev/snd/seq
getfacl: Removing leading '/' from absolute path names
# file: dev/snd/seq
# owner: root
# group: audio
user::rw-
group::rw-
other::---

Maybe this is a bug in udev or alsa?

salinas_v · 2012-03-22 06:45:13

I just tried to add myself manually to the acl on this file and it worked OK.

sudo setfacl -m u:salinasv:rw- /dev/snd/seq

Still this is a bug somewhere in udev. I have found that udev creates the snd/seq and snd/timer with the same rule 50-udev-default.rules:43

# sound
SUBSYSTEM=="sound", GROUP="audio", \
  OPTIONS+="static_node=snd/seq", OPTIONS+="static_node=snd/timer"

But if you take a closer look, you will find that they both differ on the assigned permissions:

[0]salinasv@aquelarre ~ $ getfacl /dev/snd/{seq,timer}
getfacl: Removing leading '/' from absolute path names
# file: dev/snd/seq
# owner: root
# group: audio
user::rw-
user:salinasv:rw-
group::rw-
mask::rw-
other::---

# file: dev/snd/timer
# owner: root
# group: audio
user::rw-
user:salinasv:rw-
group::rw-
mask::rw-
other::---

In 70-udev-acl.rules:29 and then :74 it is suppoused to assign the acl to everything in the "sound" subsystem.

I can't figure out why is this happening.

I have filed a bug: https://bugs.archlinux.org/task/29048

Arch Linux

#1 2012-03-18 01:15:01

Pulseaudio for multi-user breaks jack & alsa_seq/midi usage

#2 2012-03-18 09:46:10

Re: Pulseaudio for multi-user breaks jack & alsa_seq/midi usage

#3 2012-03-18 22:19:29

Re: Pulseaudio for multi-user breaks jack & alsa_seq/midi usage

#4 2012-03-18 22:34:44

Re: Pulseaudio for multi-user breaks jack & alsa_seq/midi usage

#5 2012-03-22 06:45:13

Re: Pulseaudio for multi-user breaks jack & alsa_seq/midi usage

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