How to create a dummy sound card device in Linux server?

You need to load a dummy sound driver. Please see the Alsa Wiki for detailed info, but here are the basics:

1. Load the driver:

   modprobe snd-dummy ; modprobe snd-pcm-oss ; modprobe snd-mixer-oss ; modprobe snd-seq-oss

2. Have proper .asoundrc file (you have it covered)

3. Configure autoloading of the drivers. Add this to /etc/modules.conf:

   # OSS/Free portion - card #1
   alias sound-slot-0 snd-card-0
   alias sound-service-0-0 snd-mixer-oss
   alias sound-service-0-1 snd-seq-oss
   alias sound-service-0-3 snd-pcm-oss
   alias sound-service-0-8 snd-seq-oss
   alias sound-service-0-12 snd-pcm-oss

There are actually quite a few things involved, I suggest you visit the Wiki page above for more detailed explanation.

I too had issues with this when trying to get a Dummy Sound device working on the Raspberry Pi running Raspian (derivative of Debian). The Pi on has an audio output but no input, and I want to use an application that looks for both, even though I only need an output (PJSIP).

However, the info above did not work for me and neither did the WiKi page. After speaking with a user form the ALSA mailing list, they suggested that the info on the WikI page is out of date, however, they gave me pointers as to how to solve this.

Firstly, I only need to load the 'snd-dummy' module using:

sudo modprobe snd-dummy

However, the device does not stay present after a reboot. On the Pi, this module can be loaded via the '/etc/modules' file, editing this file to load the driver produced the desired results:

sudo nano /etc/modules

My /etc/modules file simply looks like this:

# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.
# Parameters can be specified after the module name.

snd-bcm2835
snd-dummy

So, the default driver loads first, then the Dummy driver load second. Job done!

Good Luck

Chris