How to repair a damage fstab located on an LVM

i made a change to the /etc/fstab that looked perfectly fine until I rebooted the system (CentOS 6) running as a virtual machine.  The system did not start, there was a Kernel panic, and using the single boot mode did not provide any access to the system.  I changed the "/" partition to a UUID number after changing the volume name.  By any account, I am still not clear why this failed, the syntax looks sound.  This is something I have done in the past.

Anyway, I could have given up here and reinstalled the OS since this was a fresh build, but I wanted this to be a teachable moment.  Fortunately, this was time well spent.

These are the steps i took to resolve this.

  • Download the CentOS-6.5-x86_64-LiveCD.iso.
  • Mount the ISO to the system
  • Reboot the system to the ISO
  • Open a terminal window

Once here I wasn’t exactly clear what to do next, since fdisk clearly sees the hard drives, but these are logical volumes.  I will need to mount a logical volume.

  • vgscan (use this to list the volume groups, look for the volume that needs to be mounted)
  • vgchange -a y (activate all available volume groups)
  • lvscan (scan for logical volumes, and displays that the devices are now active)
  • mount /dev/my_vg/my_lv /mnt
  • vim /etc/fstab (correct the offending lines)
  • reboot
vgchange -a y
mount /dev/my_vg/my_lv mnt
vim /etc/fstab

Upon reboot, the system came back up as expected!