[PLUG] Grub 0.97: convert VM with two disk to VM with single bootable disk

[David Bridges]

There are many variables and unknowns related to what you want to do
depending on how the original VM was built and installed.  I have used
the guidelines below to do the same sort of things you are wanting to
do.

Modify the /etc/fstab entries so that they point to the correct new
locations.  Some locations probably use labels (LABEL=/boot etc) and
from what I gather from your email you are no longer using LVM and are
only using 1 partition.  If this is correct you would need to comment
out old the entry that point to /home and modify the line for / so that
it points to the correct device (/dev/vdy1).  You didn't mention what
you are doing about swap so that is an exercise left up to you.

Shutdown the VM and connect a CentOS 6 CD to it and boot it using the
CD and enter rescue mode.  You'll be asked a few questions to get
things started.  When prompted to scan for existing installations
yes/ok.  If you have things copied over and have corrected the fstab
file it should find the install and mount it all under /mnt/sysimage. 
If the install was found and mounted you should be able to install grub
using the following.

At the shell prompt type the following
chroot /mnt/sysimage
grub-install --no-floppy --recheck /dev/vdy

If the grub-install command is successful type exit to leave the chroot
and exit 1 more time to reboot.  In theory the VM should be able to
successfully boot using the new image file but there could be some
issues depending on how things got copied from the old system.

In cases similar to what you have I usually just spin up a new VM make
a copy of the /etc directory on the new system to /etc.old then use
rsync to copy everything from the old VM excluding things like /proc,
/sys, /dev, /var/log, and /boot (unless you really need something in
it).  Once the rsync completes I restore the /etc/fstab file and things
like the /etc/sysconfig/network-scripts/ifcfg* files from the /etc.old
directory.  If you did rsync /boot you should probably run the same
sort of grub-install command listed above before rebooting.  This
usually works like a charm for any distribution as long as you know
what crucial files that need to be restored.

Good luck

--
David

On Tue, 2019-04-23 at 15:05 -0700, Robert Citek wrote:
> Greetings,
> 
> How can I turn a VM with two virtual disks into a VM with a single
> virtual
> disk that boots?
> 
> I have a VM with two virtual disks, running CentOS 6.10.  The first
> disk
> (vda) has the MBR and all the boot files, i.e. vda1 is eventually
> mounted
> at /boot.  The second disk (vdb) has an LVM partition at vdb1 and
> contains
> three LVs: lv_root (/), lv_home (/home), and swap.  What I want is a
> single
> disk (e.g. vdy) that contains all the files on a single partition
> (vdy1)
> and can boot.  And I almost have that.
> 
> That is, I detached all the disks from the original VM, created a
> separate
> temporary VM with a new disk (vdy), and attached and mounted the
> disks from
> the original VM.  I then partitioned, formatted, and mounted vdy1 at
> /mnt/vdy1/.  All the lv_root files were copied to /mnt/vdy1.  All the
> lv_home files were copied to /mnt/vdy1/home.  And all the /boot files
> were
> copied to /mnt/vdy1/boot.  Given that the system is CentOS 6.1 and
> runs
> grub 0.97, how can I install Grub at vdy from this temporary VM?
> 
> I imagine I have to modify /boot/grub/device.map,
> /boot/grub/grub.conf, and
> /etc/fstab on the /mnt/vdy1 filesystem, and then run some grub
> commands.
> 
> Thanks in advance for any pointers and guidance.
> 
> Regards,
> - Robert
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