Ubuntu – Mute sound effects on Ubuntu from command line

This can be achieved by this command

dconf write /org/gnome/desktop/sound/event-sounds "false"

However, this doesn't turn off the sound volume slider effect.

To completely turn off the sound effects the closest way I've found was to live boot into a clean iso of the distro and open the System settings > Sound > Sound effects and turn these sounds off as preferred, then copy the file ~/.config/pulse/*-stream-volumes.tdb and save it. Then, to turn off the "sound effects" on an installed environment or while building a custom version of the distro do

cp saved-pulse-volumes.tdb ~/.config/pulse/*-stream-volumes.tdb

Launch this script (or setup autostart of this script on login):

#!/bin/bash -euET
{
set -o pipefail

export DBUS_SESSION_BUS_ADDRESS="${DBUS_SESSION_BUS_ADDRESS:-unix:path=/run/user/$(id -u)/bus}"
export DISPLAY="${DISPLAY:-:0}"

xscreensaver-command -watch | while read -r line ; do
    echo "handling event: $line"

    if [[ $line = LOCK* ]]; then
      volume=$(pamixer --get-volume)
      echo "current volume is $volume"
      pamixer --set-volume 0
    fi

    if [[ $line = UNBLANK* ]]; then
      echo "setting volume to $volume"
      pamixer --set-volume "$volume"
    fi
done

exit
}

Explanation: the "daemon" part of this script xscreensaver-command -watch will hang and wait for any events from xscreensaver. Whenever "LOCK" or "UNBLANK" event occurs, the sound volume will be zeroed and restored respectively.