32-bit VMs stop working after upgrade to Debian 9/Stretch

Question

Upgraded two 32-bits Debian 8 VMs to Debian 9, in VMWare 5.1.

They stopped working, and going to the console, they are giving errors of wrong CPU architecture.

What to do?

Answer 1

Debian 9 dropped supported for older 586 based CPUs.

A possible alternative is to install a newer kernel, either with:

sudo apt-get install linux-image-4.7.0-1-686-pae

or, as you can boot a 32-bit VM with a 64-bit kernel, with an hypervisor that supports 64-bits:

sudo linux-image-4.7.0-1-amd64-unsigned

From the Devel Debian mailing list

Last year it was decided to increase the minimum CPU features for the i386 architecture to 686-class in the stretch release cycle. This means dropping support for 586-class and hybrid 586/686 processors[1].(Support for 486-class processors was dropped, somewhat accidentally, in squeeze.)

This was implemented in the Linux kernel packages starting with Linux 4.3, which was uploaded to unstable in December last year.

In case you missed that change, gcc for i386 has recently been changed to target 686-class processors and is generating code that will crash on other processors. Any such systems still running testing or unstable will need to be switched to run stable (jessie).