Comment 57 for bug 1779476

NOTE: Results w/ haveged installed...

I installed gdm3 3.28.0-ubuntu1 with:

apt-get install gdm3=3.28.0-0ubuntu1 libgdm1=3.28.0-0ubuntu1 gir1.2-gdm-1.0=3.28.0-0ubuntu1

After reboot gdm3 would still not start.

After I noticed the path used I decided to:

rm -rf /var/lib/gdm3/*
rm -rf /var/lib/gdm3/.[a-z]*

After a reboot gdm3 started both w/ Xwayland and Xorg

It seems that the upgrade to kernel 4.15.0-24 together w/ gdm3 upgrade caused some corruption of the gdm3 cached contents under /var/lib/gdm3 that prevented it from starting.

IMO this is not an easy thing to troubleshoot as nothing in the logs indicated any issue.
It is could also be preventable: have the gdm3 package always clear /var/lib/gdm3 as the next start will recreate.

As it stands now, my issue of gdm3 not starting is resolved, the haveged/entropy dependency is properly tracked by bug 1779827.

Leave it up to you whether you want to use this bug to improve the gdm3 upgrade process or close it as I documented how I fixed it