I was trying to setup Timeshift for system snapshots on a work computer with Ubuntu. It didn’t work for some reason so I tried to first get rid of it. After uninstalling it, I wanted to remove, what I though, were remains of TS files in /run/timeshift, but the root partition was still mounted, so I rm-rfd the whole root, luckily except for home. And the computer has BIOS password with secure boot, so talking to IT dep about what I’ve done that is…. Or is it?
The /boot and the initramfs was still in place, so it was dropping me to emergency shell when trying to boot. Connecting external USB to see if I can mount it, hmm doesn’t show up. Quick search on my private computer what kernel modules are required for USB storage, modprobed couple of xhci_* and bang, was able to mount it. I saved result of ls -l /dev/disk/by-uuid on the drive and moved to my private PC, where I created VM and installed exact same Ubuntu with exact config (LVM+Luks) and after it was done I copied all of / content to the (now formatted as ext4) external drive using cp -a, then edited fstab and crypttab to put proper UUIDs there, set up hostname and user account accordingly. Then moved back to the borked laptop, copied the newly installed Ubuntu back to the root partition, rebooted and it worked perfectly on first try and continues to work. All of that roller coster in just a single hour.