missing sbin/hotplug in Ubuntu

Question

Im using Ubuntu and I cannot find /sbin/hotplug. Did anything replace it?
How does it handle hotplugging? I read that kernel calls it for notifying user space when an hotplug event happens. I also checked /proc/sys/kernel/hotplug , but its empty

Answer 1

From https://www.kernel.org/doc/pending/hotplug.txt we can read:

... Linux provides two interfaces to hotplug; the kernel can spawn a usermode
helper process, or it can send a message to an existing daemon listening to a
netlink socket.

and:

It's possible to disable the usermode helper hotplug mechanism 
(by writing an empty string into /proc/sys/kernel/hotplug)...

So, if your /proc/sys/kernel/hotplug is empty that means you/ubuntu are not using the 'usermode helper hotplug mechanism'.

Instead udev, as the "successor" of the old 'usermode helper hotplug mechanism', listens on a netlink socket and gets notified by the kernel about hotplug events.

I hope this helps.