Stop auto-upgrade in Ubuntu

 The simplest way to do this would be to disable every auto-upgrade. Here's how you can do it on Ubuntu 18.04 and 20.04:

1. Open Terminal (if this is an Ubuntu Server installation, just SSH into the thing)
2. Edit Apt's 20auto-upgrades file to disable everything:

sudo vi /etc/apt/apt.conf.d/20auto-upgrades

3. Ensure everything is set to 0. If done correctly, you'll have a file that looks like this:

APT::Periodic::Update-Package-Lists "0";
APT::Periodic::Download-Upgradeable-Packages "0";
APT::Periodic::AutocleanInterval "0";
APT::Periodic::Unattended-Upgrade "0";