Sharing sound between users (Fedora 8)

usernamenumber · 12-25-2007, 02:55 AM

Hi folks,

I have a Fedora 8 system where I want multiple users to be able to be logged in and able to access the sound card simultaneously. For example, if I log in as user foo at the local console, then ssh in as user bar, any attempt to run commands like "play sound.wav" results in an error like this:

Code:

ALSA lib confmisc.c:768:(parse_card) cannot find card '0'
ALSA lib conf.c:3510:(_snd_config_evaluate) function snd_func_card_driver returned error: No such device
ALSA lib confmisc.c:392:(snd_func_concat) error evaluating strings
ALSA lib conf.c:3510:(_snd_config_evaluate) function snd_func_concat returned error: No such device
ALSA lib confmisc.c:1251:(snd_func_refer) error evaluating name
ALSA lib conf.c:3510:(_snd_config_evaluate) function snd_func_refer returned error: No such device
ALSA lib conf.c:3982:(snd_config_expand) Evaluate error: No such device
ALSA lib pcm.c:2145:(snd_pcm_open_noupdate) Unknown PCM default
play stio: Failed writing default: cannot open audio device

strace shows this to be the result of the app getting permission denied when it tries to access /dev/snd/controlC0. I figured that it must be owned by the first user, foo, probably thanks to pam_console or the like, and that all I'd need to do is configure the system to grant all members of a given group rw access to the file by default.

However, upon investigation I find that this file, like everything else in /dev/snd/ is owned by root:root, so there must be more to this. I did an strace on foo successfully running play, and it shows that after controlC0 is accessed, /dev/snd/pcmC0D0p is used for the actual work, but again, everything in /dev/snd/ is root:root, so I can't figure out why foo is able to use it, let alone how to give that kind of access to bar.

If anyone can assist me with this, I will really appreciate it.

elliott678 · 12-25-2007, 03:33 AM

Does Fedora use dmix? If so something like this in your asound.conf might help, depending on you system config some changes may need to be made:

Code:

pcm.dmixer { 
    type dmix 
    ipc_key 1024
    ipc_key_add_uid false
    ipc_perm 0666			# mixing for all users
    slave { 
        pcm "hw:0,0" 
        period_time 0 
        period_size 1024 
        buffer_size 8192
        rate 44100
    }
    bindings { 
        0 0 
        1 1 
    } 
}

pcm.dsp0 { 
    type plug 
    slave.pcm "dmixer" 
} 

pcm.!default { 
    type plug 
    slave.pcm "dmixer" 
} 

pcm.default { 
   type plug 
   slave.pcm "dmixer" 
} 

ctl.mixer0 { 
    type hw 
    card 0 
}

I had to do this to allow MPD, which is runs under its own user, to work and mix while running under my user.

usernamenumber · 12-27-2007, 08:23 AM

Thanks, but the solution turned out to be even simpler. Linking to it here for others' reference.