Rules files
The udev rules are read from the files located in the system rules
directory /usr/lib/udev/rules.d, the volatile runtime directory
/run/udev/rules.d and the local administration directory
/etc/udev/rules.d. All rules files are collectively sorted and
processed in lexical order, regardless of the directories in which they
live. However, files with identical file names replace each other.
Files in /etc have the highest priority, files in /run take precedence
over files with the same name in /lib. This can be used to override a
system-supplied rules file with a local file if needed; a symlink in
/etc with the same name as a rules file in /lib, pointing to /dev/null,
disables the rules file entirely.
