[conspire] Good page about debugging Linux audio problems

[Ruben Safir]

On 10/18/2011 09:07 PM, Rick Moen wrote:
> I'm about to link this page from my knowledgebase:
>
>   'lsof | grep snd -- how to free a linux sound device'
>
> http://linux.dsplabs.com.au/lsof-grep-snd-how-to-free-a-linux-sound-device-p25/
>

There was a time when I could set up ALSA to take multiple applications 
without a problem.
It won't do  it any more.   Any clues?

Ruben

> For some months, I've been having a mysterious problem with my Debian
> workstation at work, where sound functions fine after reboot for some
> period of time, and then ceases to work from that point until the next
> reboot.  Obviously, this is not a case 'sound driver support never
> configured', nor 'sound driver will work once a non-free firmware BLOB
> gets fetched and installed'.
>
> It's not even a matter of 'funky sound daemon from a Desktop Environment
> is clobbering ALSA' or 'there are multiple sound devices, and apps are
> trying to talk to the wrong one'.  It seemed likely that some process
> was hogging a sound device file and not making it available for other
> apps.
>
> The page gives some background on how sound support on Linux has gotten
> a little messed up.  The old "Open Sound System" (OSS) driver set had
> limited hardware support unless you bought the proprietary version.
> ALSA (Advanced Linux Sound System) was supposed to fix that while being
> backwards-compatible to the old OSS interface.  But then 'help' arrived
> in the form of more-baroque would-be replacements like esound, that
> unspeakable Pulse Audio thing, and others -- all of which I carefully
> avoid, for now.  It's supposed to be a simple ALSA setup with OSS
> backwards compatibility.
>
> The cited page says do:
>
>    lsof | grep snd
>
> Good idea.  The 'lsof' tool is an ever-useful utility that does a
> (sort of) "ls" of Open Files (thus the name), showing what process
> has a file (such as a device node) open.  Yields nothing in this case,
> but, just on a hunch, I did:
>
>    lsof | grep audio
>
> Aha.  But of libs opened by _pidgin_, the IM client.  Also, I read the
> cited page more closely, and see that /dev/snd is OSS, while ALSA uses
> /dev/snd/*  :
>
> rmoen at borgia:/dev/snd$ ls -al
> total 0
> drwxr-xr-x  3 root root      240 Oct 13 16:55 .
> drwxr-xr-x 16 root root     3440 Oct 17 17:48 ..
> drwxr-xr-x  2 root root       60 Oct 13 16:55 by-path
> crw-rw----  1 root audio 116, 10 Oct 13 16:55 controlC0
> crw-rw----  1 root audio 116,  9 Oct 13 16:55 pcmC0D0c
> crw-rw----  1 root audio 116,  8 Oct 18 17:40 pcmC0D0p
> crw-rw----  1 root audio 116,  7 Oct 13 16:55 pcmC0D1c
> crw-rw----  1 root audio 116,  6 Oct 13 16:55 pcmC0D2c
> crw-rw----  1 root audio 116,  5 Oct 13 16:55 pcmC0D3c
> crw-rw----  1 root audio 116,  4 Oct 13 16:55 pcmC0D4p
> crw-rw----  1 root audio 116,  3 Oct 13 16:55 seq
> crw-rw----  1 root audio 116,  2 Oct 13 16:55 timer
> rmoen at borgia:/dev/snd$
>
>
> Kill pidgin.  Play the test sound file again:  Ah, now sound works.
>
> Damn you, pidgin:  I didn't want you to touch my sound hardware.  Just
> shut up, nei?  That'll teach me to defer checking an application's
> preferences.  Open pidgin's preferences, Sounds tab.  Change "Method"
> from "ALSA" to "No sounds'.  Close.
>
>
>
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