I could see some people wanting their NixOS instance to automatically run nixos-rebuild switch --upgrade on some schedule. Doing the obvious thing (creating a systemd job that runs periodically and runs that command) fails because you can't sensibly run nixos-rebuild inside a systemd job (see #6662).
nixos-rebuild switch --upgrade
Is there a nice way to get this behavior? The idea is that given a fixed configuration and a channel, you don't want to have to worry about keeping yourself up to date with patch releases.
Maybe use cron? Or I didn't get your question..
Is cron independent of systemd on NixOS? If it runs inside a systemd service, I'll have the same problem I describe in #6662.
Add auto update feature
You can now keep your system up to date automatically by setting:
system.autoUpgrade.enable = true;