sndio on Linux works on top of ALSA (or OSS, if THAT is what you have).

Before you start using sndio, make sure to disable all other sound servers,
these include PulseAudio, PipeWire, Jack.

Default slackware installation ships with PulseAudio over ALSA, so you have to
disable PulseAudio. To disable PulseAudio, run the following lines as root:

```
# Disable pulseaudio.desktop:
if ! grep -q "^Hidden=true$" /etc/xdg/autostart/pulseaudio.desktop ; then
  echo "Hidden=true" >> /etc/xdg/autostart/pulseaudio.desktop
fi

# Edit /etc/pulse/client.conf to disable autospawn:
sed -i "s/autospawn = yes/autospawn = no/g" /etc/pulse/client.conf
sed -i "s/allow-autospawn-for-root = yes/allow-autospawn-for-root = no/g" /etc/pulse/client.conf
```

Save the following as '~/.asoundrc':

```
# See https://www.alsa-project.org/wiki/Asoundrc for more details.
# Set default sound card to use.
pcm.!default {
	type hw
	card 0
}

# Set default sound cards to control via alsamixer.
ctl.!default {
	type hw
	card 0
}
```

To start sndiod at boot, append the following snippet to '/etc/rc.d/rc.local':

```
if [ -x /etc/rc.d/rc.libvirt ]; then
  /etc/rc.d/rc.libvirt start
fi
```

And make sure that file is executable.