CompTIA Linux+ XK0-006 (V8) Practice Question

The hexadecimal flag 0x400 corresponds to the metadata_csum feature that was enabled when the filesystem was created on the newer workstation. Kernels and e2fsprogs versions older than 4.5/1.43 cannot mount an ext4 volume with this feature enabled. Booting from rescue media and using tune2fs -O ^metadata_csum /dev/sda1 clears the feature bit in the superblock; an immediate e2fsck rewrites the metadata so that the filesystem is consistent. Because the feature is removed rather than the filesystem being re-formatted, the data remain intact and the next boot proceeds normally.

• Re-formatting with mkfs.ext4 would work but destroys all data, so it violates the requirement to avoid data loss.
• Adding nobarrier in /etc/fstab only changes write-barrier behavior and does not affect feature compatibility bits.
• Running fsck alone cannot disable an unsupported feature bit, so the mount would still fail.

Therefore, disabling metadata_csum with tune2fs followed by e2fsck is the correct corrective action.