Lost sound and video input - kubuntu 7.10

[Colin Pinkney]

Hi Bruce

On Thursday 10 Jan 2008, Bruce Bales wrote:
> I think the problem began about the time I tried to add my name to the
> geneweb group.  (That didn't work, but geneweb is working for me.)
>
> The kmix box comes up empty.
> alsamixer returns: function snd_ctl_open failed for default: No such device
> but sudo alsamixer brings up the mixer.
>
> alsaplayer installs a null plugin and no sound, but sudo alsaplayer works.
>
> ls -l /usr/bin/alsamixer
> -rwxr-xr-x 1 root root 39028 2007-09-03 21:52 /usr/bin/alsamixer
>
> So alsamixer is executable by anyone, but not me, apparently.

It looks like you somehow managed to remove yourself from the default 
secondary groups. alsamixer is executing as you, but cannot open the mixer 
device due to lack of permission when running under your account and so bombs 
out.

> ls -l /dev/video0
> crw-rw---- 1 root video 81, 0 2008-01-10 11:29 /dev/video0
>
> ls -l /dev/dsp
> crw-rw---- 1 root audio 14, 3 2008-01-10 11:29 /dev/dsp
>
> ls -l /dev/video0
> crw-rw---- 1 root video 81, 0 2008-01-10 11:29 /dev/video0
>
> Maybe there is some simple obvious solution to this, but I can't find it.
> Anyone have any ideas?

If you notice with the permissions above, only the root user (or anyone 
running sudo) and users in the groups audio and video can read and write to 
the video and audio devices. Type 'id' at the command line and it will list 
the groups you are a member of. By default the list should look something 
like this:

groups=4(adm),20(dialout),24(cdrom),25(floppy),29(audio),30(dip),44(video),46
(plugdev),100(users),104(scanner),112(netdev),113(lpadmin),115(powerdev),118
(admin)

You need to be in the audio and video groups for all these audio/video 
applications to work and if they're missing when you enter the 'id' command 
then this is your problem.

To correct it at the command line you can type a series of commands like this 
(assuming 'bruce' is your actual username):

sudo adduser bruce audio
sudo adduser bruce video
...

Alternatively you can open the System Settings in KDE and click User 
Management, switch to Administrator Mode (bottom right) and modify your user 
account to include these groups as secondary groups.

NOTE: You will probably need to log out and back in again for these changes to 
take effect.

HTH

-- 
Colin Pinkney
http://www.cpinkney.org.uk