Comment 2 for bug 1756593

Start of the log (above is only the tail end where it gets stuck during the cpio:
root@charion:/boot# update-initramfs -u -k 4.15.0-12-generic -b /boot -t -v
Keeping /boot/initrd.img-4.15.0-12-generic.dpkg-bak
update-initramfs: Generating /boot/initrd.img-4.15.0-12-generic
Copying module directory kernel/drivers/usb/host
(excluding hwa-hc.ko sl811_cs.ko sl811-hcd.ko u132-hcd.ko whci-hcd.ko)
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/host/isp116x-hcd.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/ssb/ssb.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/host/ssb-hcd.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/host/xhci-plat-hcd.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/host/r8a66597-hcd.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/host/oxu210hp-hcd.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/host/max3421-hcd.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/bcma/bcma.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/host/bcma-hcd.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/host/isp1362-hcd.ko
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/host/fotg210-hcd.ko
Copying module directory kernel/drivers/usb/c67x00
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/c67x00/c67x00.ko
Copying module directory kernel/drivers/usb/chipidea
Adding module /lib/modules/4.15.0-12-generic/kernel/drivers/usb/gadget/udc/udc-core.ko
[...]