How to change the VM Guest OS type and version information

As we all know that, we specify the guest operating system and its version during the VM creation. In case if you’ve specified the wrong operating system, version or upgrading the already installed guest OS then you will need to change the guest operating system version to reflect the same correctly in vCenter inventory.

Here in my case we just upgraded the operating system of our last remaining Server 2003 servers and want to correct the related guest OS info in vCenter inventory.

Prerequisites

Power off the virtual machine.

Procedure

• Right-click a virtual machine in the inventory and select Edit Settings. 
• Click the VM Options tab and expand General Options. 
• From the Guest OS drop-down menu, select the guest operating system family. 
• From the Guest OS Version drop-down menu, select the guest operating system version. 

• If you select Other for the guest operating system family and Other (32-bit) or Other (64-bit) for the version, in the vSphere Web Client you are prompted to type a name for the operating system in the text box. 
• Click OK. 

And you are done…

Note: When you change the guest operating system type in the virtual machine settings, you change the setting for the guest operating system in the virtual machine's configuration file. To change the guest operating system itself, you must install the new operating system in the virtual machine. 

When you set the guest operating system type for a new virtual machine, vCenter Server chooses configuration defaults based on the guest type. Changing the guest operating system type after the virtual machine is created does not retroactively change those settings. It affects the recommendations and setting ranges offered after the change. 

Why its important to select the Correct Guest OS Type/Version:

Incorrect configuration of Guest OS of the virtual machine can lead to;

• Reduction of performance
• Different default type for the SCSI device
• Different defaults of devices
• Wrong VMware Tools presented to the Guest OS resulting in failure to install
• Inability to select virtual hardware such as enhanced vmxnet, vmxnet3 or number of vCPUs.
• Inability to activate features such as CPU and Memory Hot Add.
• Inability to activate Fault Tolerance.
• VM burning up 100% of CPU when idling (rare occasions) 

Reference: http://frankdenneman.nl/2009/12/15/impact-of-mismatch-guest-os-type/ 

http://www.yellow-bricks.com/2012/01/13/why-selecting-the-correct-os-when-creatingupgrading-a-vm-is-important 

That's it... :)