Unmounting /media/usb fails during shutdown if udev is running
Attachments show two cases:
unmounting_with-udev: udev (and udev-trigger) was previously started
in the sysinit runlevel.
unmounting_without-udev: udev (and udev-trigger) was stopped before shutdown.
Installed udev packages:
(from redmine: issue id 10525, created on 2019-05-31)