Qube fails to start, "Superblock invalid"

I can boot the Qube, yet not open any apps. Opening a console shows /dev/xvdb is failing to open due to an invalid superblock. I’m unable to run fsck from the console, as it always errors with “Superblock checksum does not match superblock”/“Bad magic number”. The same is true when I run on the /dev/mapper entry for {qube}–private.

Any tips on being able to run fsck? dumpe2fs works fine and prints multiple backup superblocks. Am I missing something about the nature of /dev/xvdb? Is it not an ext4 partition directly?

Sounds like you’re on the right track. Take a look at the e2fsck manpage, in particular the -b option.

Never run filesystem utilities on (or worse: mount) VM filesystems in dom0. The filesystem on-disk format itself, and not just the files stored in it, is a complex data structure that’s fully controlled by the VM, so it’s best treated as potentially malicious. Filesystem utilities (or kernel filesystem code) can’t be assumed to be robust against this.

(It’s possible to attach the private volume to another VM in case the corruption really turns out to be severe and you need to resort to more advanced data recovery software like TestDisk.)