• You successfully installed VMware ESXi on hardware with an unsupported CPU following the steps of this guide: How to install VMware ESXi on unsupported CPUs but after a reboot you’re stuck with an error message like this:

VMB: 578:
            
Unsupported CPU: Intel family 0x06, model 0x1a, stepping 0x4
            
Intel(R) Xeon(R) CPU E5-4620 v 4 @ 2.10GHz
            
See http://www.vmware.com/resources/compatibility
        

• You installed a version of ESXi which is for your hardware CPUs (refer to: VMware - Compatibility)

1. Shut down the ESXi server
2. Remove the media where ESXi is installed on (might be an USB, a SD card or a SSD/HDD)
3. Plug the media into a PC running Windows or any other OS capable of working on FAT filesystems
4. You will see two partitions, one containing ONLY a file named BOOT.CFG and another with several files including another BOOT.CFG
5. Open the BOOT.CFG contained in the partition WITH MULTIPLE FILES with a text editor
6. Find the line starting with kernelopt= and add the string allowLegacyCPU=true at the end of the line



7. Save the file
8. Insert the boot media back into the server
9. Boot the server. If everything worked correctly ESXi should now boot automatically without the need to pass the AllowLegacyCPU=true parameter manually each time.

• This workaround is permanent, but doesn’t mean you won’t experience unexpected behavior in the future since this configuration is not officially supported.
• This workaround can be applied to virtualized (nested) ESXi hosts too by working on the .vmdk file.