VMware Tools upgrade fails with vix error code 21001 due to isolation settings in VMware vCenter Server

Products

• VMware vCenter Server

Issue/Introduction

When attempting to upgrade VMware Tools on a virtual machine managed by VMware vCenter Server, the operation fails with the following error messages:

• "The required VMware Tools ISO image does not exist or is inaccessible."
• "vix error code = 21001"
• "The VMware Tools image is inaccessible."

This behavior occurs even when the VMware Tools ISO image is manually mountable from the datastore, confirming that the underlying ISO file is intact and accessible to the ESXi host.

Environment

VMware vCenter Server 8.x

Cause

The virtual machine has the advanced configuration parameter isolation.tools.autoInstall.disable is set to TRUE. When this parameter is enabled, it explicitly prevents the automated installation or upgrade of VMware Tools for that virtual machine, causing the VIX error 21001. 

Resolution

To resolve this issue, the isolation.tools.autoInstall.disable parameter must be disabled:

1. Power off the virtual machine.
2. In the vSphere Client, right-click the virtual machine and select Edit Settings.
3. Navigate to the VM Options tab.
4. Expand Advanced and click Edit Configuration.
5. In the Configuration Parameters window, locate the parameter isolation.tools.autoInstall.disable
6. Change the value from TRUE to FALSE.
7. Click OK to save the changes.
8. Power on the virtual machine.
9. Retry the VMware Tools upgrade from the vSphere Client by right-clicking the VM > Guest OS > Install/Upgrade VMware Tools. 

Note: It is recommended to take a snapshot of the virtual machine before modifying configuration parameters.

Additional Information

VMware Tools Documentation - Installing and Upgrading VMware Tools

VMware Tools install or upgrade failed - error code = 21001

VMware Tools upgrade failed on 32-bit Windows OS