> Things can be in /etc/systemd/system/, /run/systemd/system/, /usr/lib/systemd/system/* and those are just the "basic" override locations. And those edits and masks usually don't clash with each other, so your customizations and quirks stick, even if the rest of your system changes.
I really encourage you to learn the difference between these three places. They are semantically distinct, and it's truly an advantage to have the system distinguish them. They're all sources of configuration, of course. But one is managed by the OS vendor, one by the sysadmin, and one by the sysadmin at runtime. Runtime isn't as significant a distinction, but having a clear, bright line between vendor-provided and sysadmin-managed config is huge.
I really encourage you to learn the difference between these three places. They are semantically distinct, and it's truly an advantage to have the system distinguish them. They're all sources of configuration, of course. But one is managed by the OS vendor, one by the sysadmin, and one by the sysadmin at runtime. Runtime isn't as significant a distinction, but having a clear, bright line between vendor-provided and sysadmin-managed config is huge.