How do I permanently turn off updates?

Solution 1:

If you open the App Store and under the App Store menu item click on preferences. This opens a panel where you can change or turn off updates. This is for High Sierra. It may be different in Catalina but I thought it was worth the effort to check.

Solution 2:

I'm posting this as an answer in the hope that this will solve someone elses problems.

Scenario: every time I left my backups to run or downloads running in the background I would leave my machine alone and prevent the machine going to sleep using the Energy Saver settings. I would almost always come back to find the computer turned off and then find that an Software Update had been applied but my backups had been killed and I was either switched off or the machine was back at the login screen having restarted.

I spent a huge amount of time looking through the system logs and tracing events and found that the constant logging out and restarting was down to a setting deep in the system:

System Preferences > Security & Privacy > Privacy > (unlock the lock at the bottom) > Advanced

You will now see a little checkbox called "Logout after 60 mins of inactivity"

It took me weeks to find this, and a lot of sanity and paranoia. I hope this helps someone somewhere!