Recently, I've had a hard time with my virtual machines (VMs). With the update to kernel 5.8, starting any of them caused my entire system to lockup so that even the magic sysrequest didn't help. The problem persisted from August 15th to September 9th when it was finally solved by virtualbox 6.2.14. After the update, I immediately tended to my VMs to update them.
CentOS: 0.012 packages – check.
Debian: 123 packages – check.
Archlinux: 123456 packages – ch... wait a sec, login incorrect after reboot?
My physical installations of Arch didn't exhibit such an attitude, which I thus suspected to be related to the virtualbox-guest addons of Arch (since the virtual CentOS and Debian were also behaving properly). I was wrong.
PAM had been updated to version 1.4, dropping support for the long deprecated tally module. My virtual Arch, however, is from 2009, and my /etc/pam.d/login indeed referenced this module. But there was also a login.pacnew that would have corrected this issue if I only would have bothered to handle 'pacnew' files as advised:
“These files require manual intervention from the user and it is good practice to handle them right after every package upgrade or removal. If left unhandled, improper configurations can result in improper function of the software or the software being unable to run altogether.”
I hate being in the corner with the criminally stupid, but there I am. I'll try the pacman hook in the future.