[CentOS] KVM on CentOS 6

Thu Sep 8 09:25:20 UTC 2011
Nick <oinksocket at letterboxes.org>

On 08/09/11 07:23, Emmett Culley wrote:
> Today I suddenly have two VMs that have read only file systems.  The host is
> CentOS 6, as are the two VMs with this problem.

Disclaimer: I can't claim this matches your circumstance exactly, but it is
something you might check.

I have seen problems with LVM partitions in KVM guests being unwritable, despite
being mounted read-write, on CentOS5.6 (host and guest). Specifically, I was
booting a guest from the CentOS live CD in order to fix /etc/fstab on the root
partition, which was LVM, but I could not save my changes.

Executing 'vgscan' resolved my problem; I'm not clear exactly why, but I could
then remount and write successfully.  You might also try 'vgchange -ay' if that
doesn't work.

 - boot with liveCD .iso in a virtual CD drive
 - check whether VolGroup-lv_root is mounted and writeable
   (use mount, lvdisplay, touch etc.)
 - if not, unmount it, run vgscan
 - remount it, and check for writability again