Comment 10 for bug 1705345

I have the same issue, apparently a sudo apt full-upgrade hung and I interrupted it by shutting down my laptop. Upon trying to install something unrelated it told me I had to run sudo dpkg --configure -a to continue with the previous upgrade. That still hangs:

$ sudo dpkg --configure -a
Setting up linux-image-4.13.0-21-generic (4.13.0-21.24) ...
Running depmod.
update-initramfs: deferring update (hook will be called later)
The link /initrd.img is a dangling linkto /boot/initrd.img-4.13.0-21-generic
vmlinuz(/boot/vmlinuz-4.13.0-21-generic
) points to /boot/vmlinuz-4.13.0-21-generic
 (/boot/vmlinuz-4.13.0-21-generic) -- doing nothing at /var/lib/dpkg/info/linux-image-4.13.0-21-generic.postinst line 491.
Examining /etc/kernel/postinst.d.
run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 4.13.0-21-generic /boot/vmlinuz-4.13.0-21-generic
run-parts: executing /etc/kernel/postinst.d/dkms 4.13.0-21-generic /boot/vmlinuz-4.13.0-21-generic

I can see using ps axuf that it hangs on a plymouth ping, this hangs in a terminal as well. See the attachment for the output of strace plymouth --ping