Guest Operating System Customization

You can use the vSphere Web Services SDK to customize several attributes of the guest operating system. The CustomizationSpec data object allows you to specify network and identity settings in the guest operating system.

Use the CustomizationSpec data object to specify the settings that you choose to modify. You can specify the following areas:

IP addresses and gateway addresses for virtual NIC devices
DNS servers
Virtual hostname
Domain name
Time zone

You can customize a guest operating system while the virtual machine is stopped, by invoking the VirtualMachine.CustomizeVM_Task method. You can customize the guest operating system while the virtual machine is running, by invoking the VirtualMachineGuestCustomizationManager.CustomizeGuest_Task method. The instant clone feature requires that you customize the virtual machine while it is running. To initialize a virtual machine for a cloud environment, you must customize the virtual machine while it is stopped.

The two ways to customize a virtual machine are compared in the following table.

Table 1. Comparing Guest Operating System Customization
	Customization While Stopped	Instant Clone Customization
vSphere Compatibility	vSphere 5 and later Both vSphere and VMC	vSphere 7 and later vSphere only (not VMC)
API Method	`VirtualMachine.CustomizeVM_Task()`	`VirtualMachineGuestCustomizationManager.CustomizeGuest_Task()` `VirtualMachineGuestCustomizationManager.StartGuestNetwork_Task()` `VirtualMachineGuestCustomizationManager.AbortCustomization_Task()`
Creating CustomizationSpec	Create customization specifications in vSphere Client or in API.	Create customization specifications in API.
Virtual Machine State	Must be powered off.	Must be powered on.
vmtools	Must be installed. For Linux cloud-init customization, use open-vm-tools.	Must be installed and running.
cloud-init	Must be installed if using cloud-init customization.	Not used.
Customization Engine	Not used.	Required.
Supported Guests	Both Linux and Windows. For supported versions, see https://partnerweb.vmware.com/programs/guestOS/guest-os-customization-matrix.pdf.	Linux only. Supported distributions are listed in Customizing Guest Network Settings for Running Virtual Machines.
Network Adapter State	For Sysprep or Linuxprep customization, `CustomizeVM_Task()` disconnects virtual adapters and prepares customization. The next time the virtual machine powers on, the customization will take effect and `vmtools` will reconnect virtual adapters. For CloudinitPrep customization, `CustomizeVM_Task()` does not disconnect virtual adapters.	`InstantClone_Task()` disconnects virtual adapters before creating a clone. Use `StartGuestNetwork()` to restart virtual adapters after customization.
Rebooting the Guest	`vmtools` reboots the guest operating system after reconnecting virtual network adapters. No reboot needed after Linux cloud-init customization, either LinuxPrep or CloudinitPrep.	No reboot needed. `StartGuestNetwork()` restarts network services after customization.