Every device and every interface has an associated hotplug event, which is processed by udev and the responsible hotplug agent. Hotplug events are triggered by the kernel when a link to a device is established or removed or when a driver registers or deletes an interface. Since SUSE LINUX 9.3, udevd receives and dispenses hotplug events. Either udevd listens directly to netlink messages from the kernel or /sbin/udevsend must be specified in /proc/sys/kernel/hotplug. After udevd has done its job (see Chapter 19, Dynamic Device Nodes with udev), it searches for a hotplug agent in /etc/hotplug.d/ that matches the type of event.