Problema: Solo un determinado usuario o root puede reproducir sonido en el sistema.

Salida de mplayer.

[AO_ALSA] alsa-lib: pcm_dmix.c:989:(snd_pcm_dmix_open) unable to create IPC semaphore
[AO_ALSA] Playback open error: Permission denied
AO: [pulse] Init failed: Connection refused
connect(2) call to /dev/shm/jack-1000/default/jack_0 failed (err=No such file or directory)
attempt to connect to server failed
[JACK] cannot open server

Solución: Eliminar los temporales (/tmp) o reiniciar el sistema.

rm -r /tmp/*