After update, kernel panic at boot with error: Unable to mount root fs on unknown-block(0,0)

Issue

• After a fresh install and reboot, or after a kernel update, the system fails to boot with the following message:

  VFS: Cannot open root device XXX or unknown-block(0,0)
  Please append a correct "root=" boot option; here are the available partitions:
  Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
  ...
  Call Trace:
    [<ffffffff81527213>] ? panic+0xa7/0x16f
    [<ffffffff81c27432>] ? mount_block_root+0x216/0x2cb
    [<ffffffff81002930>] ? bstat+0x2b0/0x980
    [<ffffffff81c2753d>] ? mount_root0x56/0x5a
  

• OS unable to boot after kernel upgrade on RHEL 7

  

• When upgrading the system (and the kernel in the process), the server doesn't reboot anymore.