How to clone existing KVM virtual machine images on Linux

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I wanted to clone my Debian or Ubuntu Linux KVM VM for testing purpose. How do I clone existing virtual machine images under KVM?

You can use a simple command named virt-clone. It is a command line utility for cloning existing virtual machine images using the “libvirt” hypervisor management library. It will copy the disk images of any existing virtual machine, and define a new guest with an identical virtual hardware configuration. Elements which require uniqueness will be updated to avoid a clash between old and new guests.

How to clone your VM and spawn new instances in KVM

The syntax is
# virt-clone --original {Domain-Vm-Name-Here} --auto-clone
OR
# virt-clone --original {Domain-Vm-Name-Here} \
--name {New-Domain-Vm-Name-Here}

Examples

First VM/domain with devices to clone must be paused or shutoff. To gracefully shutdown a domain named ubuntu-box1, run:
$ sudo virsh shutdown ubuntu-box1
OR you can paused it as follows:
$ sudo virsh suspend ubuntu-box1
$ virsh list

Sample outputs:

Domain ubuntu-box1 suspended

 Id    Name                           State
----------------------------------------------------
 1     freebsd                        running
 5     ubuntu-box1                    paused

Let us generate a new guest name, and paths for new storage automatically for a vm called ubuntu-box1
$ sudo virt-clone --original ubuntu-box1 --auto-clone
Sample outputs:

WARNING  Setting the graphics device port to autoport, in order to avoid conflicting.
Allocating 'ubuntu-box-1-clone.qcow2'                                                              |  40 GB  00:00:04     

Clone 'ubuntu-box1-clone' created successfully.

The above command cloned the guest called “demo” on the default connection, auto generating a new name called ubuntu-box1-clone and disk clone path. You can start or resume original domain:
$ sudo virsh start ubuntu-box1
OR
$ sudo virsh resume ubuntu-box1
Next, start ubuntu-box1-clone, enter:
$ sudo virsh start ubuntu-box1-clone
Verify it:
$ virsh list
My dhcpd server gave 192.168.2.147 IP address to ubuntu-box1-clone VM, run:
$ ping -c2 192.168.2.147
Finally, ssh into the box:
$ ssh [email protected]
Sample sessions:

Fig.01 virt-clone command cloned existing virtual machine images
Fig.01 virt-clone command cloned existing virtual machine images

Please note, virt-clone does not change anything inside the guest OS, it only duplicates disks and does host side changes. So things like changing passwords, changing static IP address, ssh-keys, hostnames etc are outside the scope of this tool. Once login using to cloned VM using ssh, you can change those:
$ ssh [email protected]
$ sudo -s
# echo 'ubuntu-box1-clone' > /etc/hostname
# sed -i 's/ubuntu-box1/ubuntu-box1-clone/g' /etc/hosts
# reboot
# /bin/rm -v /etc/ssh/ssh_host_*
# dpkg-reconfigure openssh-server
# passwd vivek

You can use virt-sysprep instead of virt-clone if you need to clone the VM and make/reset anything inside the guest OS.

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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