Dear Experts, I've just rebooted an AWS instance running buster and it has failed to restart, with the message "symbol 'grub_calloc' not found" shown on the console screenshot.
It's a fairly vanilla Debian installation originally from an official image and upgraded to buster. Unattended Updates are enabled (as is the default). Searching found this bug report: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=966575 Message 40 says that this occurs with the stable security updates, which presumably I have received. I note also that message 95 says "This configuration error is normally the result of something like changing disks around without telling the GRUB packaging about it, so it continues to install to an old device without realising it isn't the one that your firmware is configured to boot from any more." That could be relevant as I have at some point changed from an instance type where the root device was /dev/*hda to /dev/nvme*, and had to change fstab to use a UUID to make that work. So it's possible that the grub update has attempted to update a non-existent /dev/*hda and left the nvme root device borked. I think I would be able to fix this on a physical computer but (i.e. by booting from a USB device, or net-booting, or moving the disk to another system), but I don't know what to do with an EC2 instance. Can I start another instance and mount the borked instance's EBS root filesystem on it? "Idiot-proof" instructions would be great. Advice would be very much appreciated. I guess it would be educational to learn how good my backups are, but I'd much rather not have to do that. Thanks, Phil.
