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Using VMware vSphere VM Customization Specification

Deploying virtual machines is a basic part of VMware vSphere administration. Virtual machines are deployed, cloned, etc. Customizing the guest operating system can be a very labor intensive set of tasks from a provisioning standpoint. Thankfully, the VM Customization Specifications tool can be leveraged to take a lot of the heavy lifting out of this process. We can choose to utilize the Custmization Specification to customize guest operating systems with cloning or in customizing an existing guest operating system that is powered off. Let’s take a look at Using VMware vSphere VM Customization Specification and how create the specification to use with customizing a guest operating system.

Creating VMware VM vSphere Customization Specification

To create our new Customization Specification, we navigate to Policies and Profiles in our vCenter web client or Flash client.  Below, I am using the newest HTML5 web client that is available.  See how to use the most current HTML5 web client available with the HTML5 web client fling.  Below we have navigated to the Policies and Profiles screen where we can click the New button to add a new Customization Specification.

Create VM Customization Specification

The New VM Guest Customization Spec wizard begins.  The first screen allows us to customize the Name and target OS of the virtual machine.  Note here we can select both Windows and Linux, use a custom SysPrep answer file and control how SIDs are handled.

Customize the name and target OS

Next, we set the Registration information with the Owner name and Owner Organization.

VM Customization Specification customize registration information

We can decide how we want to handle the computer name creation.  There are three options here:  User the virtual machine nameEnter a name in the Clone/Deploy wizard, and Enter a name.

Choose how to customize the computer name

We can choose whether or not we want to specify Windows licensing information as well.

Specify the Windows licensing information

Set the administrator password and choose whether or not to automatically login.

Set the administrators password

Configure the time zone for the virtual machine.

Customize the time zone for the virtual machine

If we have any commands we want to run the first time a user logs in, we can add those on the Commands to run once screen.

Add commands to run the first time a user logs in

Network connectivity can be configured as well.  We can use standard network settings or manual select custom settings for the virtual machine.

Specify virtual machine network settings

Workgroup or domain allows us to choose which we want to join our virtual machine to.

Choose whether to join domain or workgroup

Review the settings screen to make sure we have everything we want to configure in VM customization specification.

Finalize the customization specification

Using VMware vSphere VM Customization Specification

Now that we have the VM customization Specification created, let’s see what we can do with it.  Below you should see your newly created VM customization specification listed.

Verify we have the new VM customization specification in Policies and profiles

If we choose to clone a virtual machine, on the customize guest OS screen we will see the VM customization specification listed.

Use VM Customization Specification during cloning

If we have an existing virtual machine, we can power off the virtual machine and run the customization specification against the existing virtual machine by right clicking the virtual machine and choosing Guest OS >> Customize Guest OS.

Customize an existing virtual machine with VM Customization Specification
vCenter task to run VM Customization Specification

The VM customization specification should be applied to the virtual machine and should reboot after settings have been applied.

Verifying VM Customization Specification was successful

To verify the VM Customization Specification was successful we can quickly take a look at the owner information on our virtual machine to see if it has been successfully changed.

Verify VM customization specification was successful


Using VMware vSphere VM Customization Specification is a great way to take a lot of the mundane heavy lifting out of provisioning a virtual machine.  The VM customization specification is easily created and can be used for mass deployments, etc.  Also powerful is that it can be applied to new clones, deploying from template, and existing virtual machines that are powered off.

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Brandon Lee

Brandon Lee is the Senior Writer, Engineer and owner at and has over two decades of experience in Information Technology. Having worked for numerous Fortune 500 companies as well as in various industries, Brandon has extensive experience in various IT segments and is a strong advocate for open source technologies. Brandon holds many industry certifications, loves the outdoors and spending time with family.

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