hotplug

file: /proc/sys/kernel/hotplug
variable: kernel.hotplug
Official reference

Path for the hotplug policy agent. Default value is CONFIG_UEVENT_HELPER_PATH, which in turn defaults to the empty string.

This file only exists when CONFIG_UEVENT_HELPER is enabled. Most modern systems rely exclusively on the netlink-based uevent source and don’t need this.