Who has not had that under Linux already, that super blocks are shot dead. The Superblock contains information about the management of the file system used:
But what if you see yourself confronted with such a syslog message and nothing works?
mount: wrong fs type, bad option, bad superblock on /dev/nbd0p2, missing codepage or helper program, or other error
Most of the time you can not access the file system anymore. In my case that was a proxmox image of a VM, which then could not be started.
In my case, I first made a copy of the image on a sufficiently large other partition with dd. This takes different lengths depending on the size, but is necessary because the copy always works better and freer.
The first tool is
fdisk /dev/nbd0
In this way I can show the distribution of the partitions. And with
e2fsck -f /dev/nbd0p1
I do a filecheck. With
mke2fs -n /dev/nbd0p1
I will be shown the super blocks, which I can then repair with.
e2fsck -f -y -b <Superblock> /dev/nbd0p1
Finally, the partition can be mounted on again
mount /dev/nbd0p1 /mnt
and I come back to the lost data believed. For me it was important configuration files, which I had urgently needed when reinstalling the VM, after all, it was a week's work.