Before the advent of systemd, my /tmp was cleaned when and only when I rebooted my machine. I was happy.
Now systemd has changed this decades-old default so that my /tmp is cleaned every 24 hours, it seems. I am not happy.
How to get the old please-do-not-touch-my-/tmp-except-when-rebooting behavior with systemd?
I've seen related Q&A's here, but the answers are all too complicated for me: