How Does a Cloning Machine Work? | VM Copying Explained

Whether you’re spinning up a test server or replicating a production workload, cloning a virtual machine (VM) is one of the fastest ways to deploy identical systems. The process copies the source VM’s virtual disks and settings, then adjusts machine-specific details like the VM name and hardware identifiers so the new instance runs without conflicting with the original.

The result is a separate machine with its own storage that still contains all the data the source had at the moment you cloned it.

What Actually Happens When You Clone a VM

Cloning works in three basic steps: copy the configuration, copy the disk image, and make the copy unique. The configuration file defines the VM’s virtual hardware, while the disk image holds the operating system, applications, and files. Simply duplicating both files isn’t enough because the copy would share the same name and identifiers as the source, causing conflicts on the network.

The cloning tool rewrites those uniqueness-sensitive settings automatically in most workflows. For instance, Red Hat’s virtualization documentation for RHEL 9 and 10 explains that configuration adjustments are made to ensure the clone’s identity differs from the source.

Full Clone vs. Linked Clone: What’s the Difference?

Most hypervisors offer two cloning modes, and choosing the wrong one can create an unintended dependency. Oracle VM VirtualBox’s documentation describes both clearly.

• Full clone: A complete, independent copy of the source’s disk images. It can run without the original VM and doesn’t rely on it in any way. This is the safer default.
• Linked clone: Uses differencing disks based on the source VM’s disks. It’s faster to create and uses less storage, but it depends on the source disks. Deleting the source can break the clone.

Linked clones are handy for temporary test environments, but full clones are the right choice when you need a standalone machine. If you’re weighing a purpose-built device over a general-purpose VM setup, our roundup of the best cloning machines on the market covers hardware alternatives worth considering.

How to Clone a VM in the Major Hypervisors

Every major platform has its own workflow, but the core logic is the same. Here’s how it works in the three most common environments.

Red Hat Enterprise Linux (RHEL 9/10)

Red Hat’s web console offers the simplest route. Log in, open the Virtual Machines interface, select the VM’s menu, choose Clone, optionally enter a new name, then confirm. The command-line alternative uses virt-clone, though Red Hat advises preparing the source VM first. Some versions recommend running virt-sysprep to remove machine-specific data like SSH host keys before cloning.

Oracle VM VirtualBox

Right-click the VM in VirtualBox Manager, choose Clone, then specify a new name and storage path. You’ll pick the clone type (full or linked) and the snapshot scope — this determines whether you copy the current state or a previously saved snapshot. You can also use the VBoxManage clonevm command for scripted cloning.

VMware vSphere 8.0

In the vSphere Client, select the VM and choose Clone an existing virtual machine. Proceed through the creation wizard to set the name, location, and resources. The wizard handles the unique identifier rewrite automatically.

Critical Caveats: What Most People Get Wrong

Cloning is straightforward, but a few mistakes cause real headaches. The most common error is skipping source preparation. If you clone a VM that’s running a web server with active sessions, the clone carries those sessions forward, creating unpredictable behavior. Always shut down the source cleanly and purge machine-specific data where practical.

Network conflicts are the second issue. The clone may have the same MAC address as the source, causing both machines to fight for the same identity on the network. Most modern hypervisors regenerate the MAC address automatically, but older workflows may require manual changes.

Finally, remember that cloning copies current data. Any sensitive files on the source at clone time exist on the clone too. Sanitize the source before cloning if you plan to share the clone with others.