What is the purpose of the filesystem located at /etc/udev/rules.d?

The filesystem located at /etc/udev/rules.d is primarily intended to contain system-wide udev rules. Udev is the device manager for the Linux kernel, and it dynamically creates and removes device nodes in the /dev directory based on rules defined in various files. The rules in /etc/udev/rules.d are applied to control how devices are managed and how they interact with the system.

This directory is specifically for rules created or customized by system administrators. These rules can define how udev should recognize, configure, and manage hardware devices based on certain criteria, such as the device's attributes. In contrast, files stored in /lib/udev/rules.d contain the default system-wide rules that come with installed packages and distributions.

Understanding this important distinction helps clarify that /etc/udev/rules.d is indeed the right location for local administration rules, as opposed to volatile rules or those that are only temporary, which would not fit the purpose of this particular filesystem location. While udev does manage devices, it is not accurate to state that the folders purpose is limited to defining hardware devices without considering the context of the rules that govern that management.