You can use vSphere Host Update Utility to upgrade ESXi 3.5 hosts to ESXi 4.0.

vSphere Host Update Utility is meant for small deployments in which a host is being managed by a single administrator. For example, the following scenario is not supported: Admin 1 starts to upgrade host1 using vSphere Host Update Utility. Admin 2 starts the vSphere Host Update Utility, sees that host1 is running ESXi 3.5, and tries to upgrade the host. The vSphere Host Update Utility does not report that an upgrade is already in progress.

VMware supports and recommends that you perform one upgrade at a time when you use vSphere Host Update Utility. If you do upgrade multiple hosts simultaneously and the upgrade fails for one of the hosts, you must close and restart vSphere Host Update Utility to retry the upgrade on the host that failed. In this case, you must wait until the upgrade for all the hosts is complete before you restart the utility. For simplicity, it is best practice to upgrade one host at a time.


For large deployments and for environments with clustered hosts, VMware recommends that you use vCenter Update Manager instead of vSphere Host Update Utility. See the vCenter Update Manager Administration Guide.

When you upgrade a host, no third-party management agents or third-party software applications are migrated to the ESX 4.0/ESXi 4.0 host.

Prepare the host before you upgrade it.

See ESX Hardware Requirements and Recommendations for Enhanced ESX Performance.

Make sure you are logged in to an account that has administrator permissions on your computer.


Download an ESXi 4.0 ZIP file and save it on the same Windows computer on which vSphere Host Update Utility is installed.


Use the vSphere Client to put the host into maintenance mode.


Select Start > Programs > VMware > vSphere Host Update Utility 4.0.


Select a host from the list and click Upgrade.

If a host is not in the list, you can add it by selecting Host > Add Host.


Type the location of the ESXi 4.0 upgrade file to use or click Browse to select the location from a file browser and click Next.

For ESXi 4.0, the installation file is a ZIP file.


Select I accept the terms of the license agreement and click Next.


Type the administrative account information for the selected host and click Next.

The software performs a host compatibility check.


Click Finish.

The host upgrade begins. You can view the upgrade progress in the Host Details pane.

When an upgrade is in progress, do not exit vSphere Host Update Utility.

The host is upgraded to ESXi 4.0. If the upgrade fails, restart vSphere Host Update Utility before you retry the upgrade.

vSphere Host Update Utility might appear to stop working. If this happens, wait several minutes to see if the utility starts working again. VMware recommends that you do not cancel the upgrade at any point during the upgrade process. The host might appear to successfully boot into ESXi 4.0. If this happens, continue to wait until the message Upgrade Succeeded appears before you close the utility.