[mythtv-users] Alsa only seems to work with Root user not mythtv user

[Michael T. Dean]

Mark Rissberger wrote:

> Michael T. Dean wrote:
>
>> Mark Rissberger wrote:
>>
>>>   First off, I'd like to thank everyone that helped me get LIRC 
>>> working with the PVR150.  It works like a dream now.  The problem 
>>> that I have now seems like it may be a permission issue but I'm not 
>>> sure where.  I can't use ALSA if I'm logged in as the mythtv user 
>>> but it works fine if I'm logged in as root.  Here is what I get as 
>>> root and as mythtv:
>>>
>>> [root at mythbox /]# aplay /usr/share/sounds/KDE_Startup.wav
>>> Playing WAVE '/usr/share/sounds/KDE_Startup.wav' : Signed 16 bit 
>>> Little Endian, Rate 22050 Hz, Mono
>>> [root at mythbox /]# exit
>>> exit
>>>
>>> [mythtv at mythbox /]$ aplay /usr/share/sounds/KDE_Startup.wav
>>> ALSA lib pcm_dmix.c:797:(snd_pcm_dmix_open) unable to create IPC shm 
>>> instance
>>> aplay: main:533: audio open error: Permission denied
>>>
>>> Here are the permissions of /dev/audio and /dev/dsp:
>>>
>>> [mythtv at mythbox /]$ ls -l /dev/au*
>>> crwxrwxrwx  1 mythtv root 14, 4 Oct 18 03:24 /dev/audio
>>> [mythtv at mythbox /]$ ls -l /dev/dsp
>>> crwxrwxrwx  1 mythtv root 14, 3 Oct 18 03:24 /dev/dsp
>>>
>>>
>>> Any ideas????   
>>
>> ls -al /dev/snd
>>
>> to show ALSA devices.
>>
>> Most likely you'll see a group called "audio" or something.  Then, 
>> just add mythtv user to the audio group.  If not (i.e. if owner and 
>> group are root), fix the permissions (probably in udev scripts-- 
>> http://www.reactivated.net/writing_udev_rules.html ).
>
> Its really odd.  Now that I've changed the group on '/dev/snd/*',  
> '/dev/shm', '/dev/dsp', and '/dev/audio' to mythtv, everything works 
> fine.  Until I root plays a sound and then I'm right back to the above 
> error msg, unable to create IPC shm instance.
>
> Why would this be?  root must be doing something to the devices when 
> it plays a sound.  Any ideas?
>
> Thanks for the above help.  At least I've gotten this far.

It would be much easier to guess with a full description of the commands 
you executed.  You said you changed the group on the ALSA devices.  Did 
you a) change it from the command line (in which case your system is 
still configured to set it to the original group), b) change the udev 
scripts to set the group to mythtv (instead of a more appropriate group 
like audio--to which the mythtv user should be added), or c) execute 
some other commands that I can't even imagine.

Note, also, that many display managers assign ownership of certain 
devices (like consoles and audio devices) to the user that logs in.  
It's possible you have something like that re-assigning ownership.  In 
other words, there are just too many plausible explanations to guess 
without more info.  And, the most likely guess is that you "treated the 
symptom and not the problem" in which case debugging would be a waste of 
time.

Oh, and BTW, root should never execute any commands that play sound, 
anyway.  After all, what do you think this is, Windows? ;)

Mike