Ubuntu 19.04 doesn't remember audio settings between reboots. This means that after every reboot I need to mute sound again and again. Since making it remember volume between reboots is hard, I went for the next best thing - mute it on reboot to start with.
Command is easy:
amixer set Master mute
To perform it on every startup, we can use
@reboot crontab directive. However, be careful which crontab you're editing as this statement is applicable only for root. It will simply be ignored for any other account's crontab.
Keeping that in mind, this is what sorted it out for me
sudo crontab -e
@reboot /usr/bin/amixer set Master mute
Now my laptop starts muted and any unmuting is left to my discretion.