> In addition to /etc/systemd/system, the drop-in ".d/" directories for system services can be placed in /usr/lib/systemd/system or /run/systemd/system directories. Drop-in files in /etc/ take precedence over those in /run/ which in turn take precedence over those in /usr/lib/. Drop-in files under any of these directories take precedence over unit files wherever located. Multiple drop-in files with different names are applied in lexicographic order, regardless of which of the directories they reside in.
> ...
And this is just an excerpt which doesn't cover the details. Read the manpage for all the hilarity.
Over-elaborated hierarchies where configuration files may reside, and their precedence schemes.
E.g. from systemd.unit manpage ( https://www.freedesktop.org/software/systemd/man/systemd.uni... ):
>...
> In addition to /etc/systemd/system, the drop-in ".d/" directories for system services can be placed in /usr/lib/systemd/system or /run/systemd/system directories. Drop-in files in /etc/ take precedence over those in /run/ which in turn take precedence over those in /usr/lib/. Drop-in files under any of these directories take precedence over unit files wherever located. Multiple drop-in files with different names are applied in lexicographic order, regardless of which of the directories they reside in.
> ...
And this is just an excerpt which doesn't cover the details. Read the manpage for all the hilarity.