stop_all() {
	systemctl stop systemd-udevd-control.socket
	systemctl stop systemd-udevd-kernel.socket
	systemctl stop systemd-udevd.service
	systemctl stop systemd-udev-trigger.service
	systemctl stop systemd-udev-settle.service
}

# If you stop the udevd sockets after the service, you might see:
# "Job for systemd-udevd.service canceled."

# If you do not stop the sockets, you might also see the message,
# and the job (applying a udev rule) will be finished after a long
# time by the udevd spawned

trigger_systemd() {
	systemctl start systemd-udevd.service
	systemctl start systemd-udev-trigger.service

	#sleep 1
	#systemctl start systemd-udev-settle

	stop_all
}

# Udevd will wait for its timeout (30s by default) but not finish its job

trigger() {
	/usr/lib/systemd/systemd-udevd --daemon
	udevadm trigger --action=add --type=devices
	echo $?

	#sleep 1
	#udevadm settle

	udevadm control --exit
	echo $?
}

# Udevd will exit immediately no matter in spite of the timeout params
# of all commands

stop_all
#trigger
#trigger_systemd

# The settle service/command serve as a reference here.
# I am not sure if it is supposed to be the "safe guard" for this issue.
# But if it works here, it is only because provide extra overhead,
# not because of its internal mechanism.