Is a "user question" acceptable on this list? When helping a friend with a system that wouldn't boot, we investigated the file system from a live image. It turned out that a lot of files had had their contents replaced with a completely different file's contents. As an example, the libuuid.so.1.3.0 file had the contents of the README file from the zfs-fuse package. They still had different inode numbers; they were not links to the same. There were at least dozens of files "replaced" in that way, we stopped searching after fixing a few. This started after an abrupt unplanned power loss, so a fsck on reboot was expected. But how could it possibly have such a drastic effect? In case it is relevant, it was on a Fedora 34, initially installed before btrfs was default on Fedora, and upgraded since.
