Someone asked the same question a few months ago, but the answer assumed a graphical desktop. In my case, the platform is headless. The problem is that I want a USB DAC, if one is connected, always to be the default sink. I can use pacmd to set the default sink to the index of the USB DAC. If I reboot the system, the USB DAC remains the default. However, the moment I disconnect the USB DAC, the default changes to the internal DAC (the only other card). If I then reconnect the USB DAC, the default remains the internal DAC. I have to run pacmd again to restore the default selection to the USB DAC. It is difficult to do that because the system is headless. I think I know a solution. I am considering creating a udev rule that responds to the attachment of the USB DAC. Maybe: ACTION=="add", SUBSYSTEM=="snd", SUBSYSTEMS=="usb", RUN+="/usr/local/bin/udev- usb-dac.sh" It calls a shell script that runs pulseaudio -k && pulseaudio --start --log-target=syslog so that the USB DAC will be assigned index 1 again (otherwise, I won't know what index to use in the next step). Then the script will run pacmd set-default sink 1 to restore the default assignment. I haven't tried it yet because it seems to me that this problem is not unusual, so surely there is a simpler solution completely within the domain of pulseaudio. Actually, the udev rule that I described will not run, so it seems that I don't have a possible solution. Any suggestions welcome.
