Linux 2.6 interface

Introduction

The Linux 2.6 hotplug interface introduced a new approach. Instead of spawning a new process for each event, thus possibly creating an unmanagably large ammount of processes, the events (uevents) are written into a PF_NETLINK socket.

The uevent has following format: actiontype@ENVVAR=VALUE\0[ENVVAR=VALUE\0[...]]

The actiontype might be "add" or "remove". The action is also exported in an environmental variable ACTION.

Reading these events by a single daemon that performs relevant actions is a far better approach, as it also allows smart distribution of resources and processing by rules, both of these features being used in both udev and hotplug2.

The old /proc/sys/kernel/hotplug interface is still kept though, and can be used. If a valid value is passed to it, the application specified in the procfs entry gets executed along with the new method of sending event through netlink socket.