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Re: [Qemu-discuss] Using qemu to run a physical machine in parallel
From: |
Jakob Bohm |
Subject: |
Re: [Qemu-discuss] Using qemu to run a physical machine in parallel |
Date: |
Sun, 4 Aug 2019 18:46:55 +0200 |
User-agent: |
Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 |
On 04/08/2019 17:26, Yassine Chaouche wrote:
Dear qemu,
I have installed Linux Mint on my machine on /dev/sda5. Later, I
installed MX Linux on /dev/sda9, but the installation of MX eventually
didn't work well as I tried to do things. I need to fix MX linux, but
each I change something I need to reboot the machine to see if it
fixed it, and this is cumbersome/tiresome/awkward. What I would like
to do is boot on /dev/sda5 (Linux Mint) and run MX Linux (/dev/sda9)
in parallel. Can I achieve this with qemu ? I don't want to reinstall
MX as a virtual machine, I would like to run and fix the already
installed one.
Thanks for your tips !
In general, qemu can use your physical hard disk partition (/dev/sda9) as a
the storage for a virtual machine disk (such as /dev/sda), thus almost
allowing you to run your MX system under qemu, however there are some
important
differences between the virtual and real machine that you will need to work
aroundyourself.
1. The virtual machine will have different "hardware", for example it will
have a different network card (at least a different mac address) and a
different graphics card. It will also have less memory because it
has to
fit inside the free memory not used by your Mint system.
2. If you mount /dev/sda9 as a virtual hard drive, the virtual machine will
see it as a physical disk, not a partition of a physical disk. This may
confuse the MX startup scripts and configuration.
As an alternative, you can layer a qcow2 image on top of the full
/dev/sda,
thus showing the virtual machine the entire disk, but redirecting all
disk
writes by MX to the qcow2 file. Beware however that because the actual
/dev/sda is changing every time your Mint system writes to it, the
content
of the Mint and shared partitions as seen by the virtual machine will
be a
garbled mess that you should not access. Once you find a working MX
setup,
you will have to copy out _only_ the MX-only partition content to the
real
/dev/sda partitions while not using or overwriting the partitions
belonging
to Mint or shared, probably by doing funny stuff with qemu-nbd and
dd, very
very carefully.
Tip: To make a small shared partitions (such as boot or EFI) completely
separate for the virtual machine, mount the qcow2 image with qemu-nbd
(without
the virtual machine running!) and very carefully dd the initial
contents of
the physical partition to the qcow2 partition. I am not sure which
additional
options are needed to prevent qcow2 from mapping those sectors back
to the
physical sectors that will change later.
3. If MX installs Linux kernels or bootloaders into common "boot" and/or
"EFI"
partitions, you will have to manually copy those files out to the Mint
machine, then pass the kernels and initramfs images on the qemu
command line
to boot them.
Some configuration tips may be gleaned from "PV" (Physical to Virtual)
conversion
instructions and scripts, but with the key difference of not actually
trying
to store a complete copy of your physical /dev/sda inside itself.
Enjoy
Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S. https://www.wisemo.com
Transformervej 29, 2860 Søborg, Denmark. Direct +45 31 13 16 10
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