gce/ERR/2021_005
Serial logs don’t contain mount error messages.
Product: Compute Engine
Rule class: ERR - Something that is very likely to be wrong
Description
The messages: “You are in emergency mode” / “Failed to mount” / “Unrecognized mount option” in serial output usually indicate that a Linux instance cannot mount the root partition.
Remediation
Make sure that root filesistem is healthy and the bootloader (grub) configuration is correct. Restore the boot disk from a snapshot.