update-kernel script -- mounting /media/usb failed
update-kernel
%<...
mount: mounting /dev/sda1 on /media/usb failed: Resource busy
The situation is probably associated with the transition modloop to overlayfs.
Detailed output and other details: https://pastebin.com/raw/NEaHuSNU
(from redmine: issue id 10527, created on 2019-05-31)