Objective

The following instruction will explain how to clone KVM-based Virtual Machines on Redhat Linux from command line using virt-clone command.

Operating System and Software Versions

  • Operating System: - Redhat 7.3
  • Software: - libvirtd (libvirt) 2.0.0

Requirements

Privileged access to your Redhat Linux installation will be required.

Difficulty

EASY

Conventions

  • # - requires given command to be executed with root privileges either directly as a root user or by use of sudo command
  • $ - given command to be executed as a regular non-privileged user

Instructions

Obtain Source Virtual Machine's information

Before we begin cloning any virtual machine we first need to obtain some basic information about it. The absolute minimum information required about the source virtual machine we are about to clone would be its name and number of disk in use. To get virtual machines name run:
# virsh list
 Id    Name                           State
----------------------------------------------------
 1     server1.linuxconfig.org            running
Next, we may would like to know the number of disk our source virtual machines is using as well as its location. The information about disks location is optional as it only provides us with a hint on where to store new clone disk files for the sake of consistency:
 # virsh dumpxml server1.linuxconfig.org | grep "source file"
      <source file='/var/lib/libvirt/images/server1.linuxconfig.org.qcow2'/>
      <source file='/var/lib/libvirt/images/server1.linuxconfig.org-1.qcow2'/>
      <source file='/var/lib/libvirt/images/server1.linuxconfig.org-2.qcow2'/>
From the above output we can see that our original virtual machine has three disks stored in location /var/lib/libvirt/images/.

Suspend Source Virtual Machine

Before cloning can take place our source virtual machine needs to pause/suspended:
# virsh suspend server1.linuxconfig.org
Domain server1.linuxconfig.org suspended

Auto-Clone Virtual Machine

One way of cloning KVM-based Virtual Machines on Redhat Linux is to use --auto-clone switch. The main advantage of --auto-clone switch is that it automatically clones any number of source disks hence the user does not necessary need to know the location and number of the disk attached to the original virtual machine.

The disadvantage is that the user is unable to specify disk names and pride an alternative location to new cloned virtual disks. The following command will clone original virtual machine server1.linuxconfig.org to new clone virtual machine server2.linuxconfig.org automatically using --auto-clone switch.
# virt-clone --original=server1.linuxconfig.org --name=server2.linuxconfig.org --auto-clone
WARNING  Setting the graphics device port to autoport, in order to avoid conflicting.
Allocating 'server2.linuxconfig.org.qcow2'                                      |  10 GB  00:00:00     
Allocating 'server1.linuxconfig.org-1-clone.qcow2'                              | 5.0 GB  00:00:07     
Allocating 'server1.linuxconfig.org-2-clone.qcow2'                              | 5.0 GB  00:00:00     
Clone 'server2.linuxconfig.org' created successfully.
As we can see from the above output the --auto-clone automatically cloned all virtual disks attached to the original virtual machine and appended clone keyword to any additional disks. New cloned virtual machine should be now waiting in shut off state to be started:
# virsh list --all
 Id    Name                           State
----------------------------------------------------
 1     server1.linuxconfig.org            paused
 -     server2.linuxconfig.org            shut off

Clone Manually Multiple Disk

To gain more control over the new cloned disk location and name we can omit the --auto-clone switch and supply all new cloned disk name and destination path using --file switch. Note the number of --file arguments supplied must be equal to the number of disks attached to the original virtual machine. Example:
# virt-clone --original=server1.linuxconfig.org --name=server2.linuxconfig.org --file /var/lib/libvirt/images/server2.linuxconfig.org.img --file /var/lib/libvirt/images/server2.linuxconfig.org-1.img --file /var/lib/libvirt/images/server2.linuxconfig.org-2.img
WARNING  Setting the graphics device port to autoport, in order to avoid conflicting.
Allocating 'server2.linuxconfig.org.img'                                                                                                                                                            |  10 GB  00:00:00     
Allocating 'server2.linuxconfig.org-1.img'                                                                                                                                                          | 5.0 GB  00:00:07     
Allocating 'server2.linuxconfig.org-2.img'                                                                                                                                                          | 5.0 GB  00:00:00     
Clone 'server2.linuxconfig.org' created successfully.

Resume/Start

At this stage we are ready to resume our original virtual machine server1.linuxconfig.org:
# virsh resume server1.linuxconfig.org
Domain server1.linuxconfig.org resumed
and also start the newly cloned virtual machine server2.linuxconfig.org:
# virsh start server2.linuxconfig.org
Domain server2.linuxconfig.org started
Check the state of all virtual machines:
# virsh list --all
 Id    Name                           State
----------------------------------------------------
 1     server1.linuxconfig.org            running
 3     server2.linuxconfig.org            running