Fsck
From Dikapedia
UNDER CONSTRUCTION
https://www.tecmint.com/fsck-repair-file-system-errors-in-linux/
BE SURE TO UMOUNT THE FILESYSTEM BEFORE RUNNING FSCK!!!!
e2fsck - ext2 I believe. But fsck will detect it
If the root filesystem is getting mounted as "Read-only" (ro) then you will need to detach it, attach it to another instance as a secondary volume, and run fsck.