Which I assume get wiped on he reboot.

So, what's next?

So each time it completes OK, but then just reboots to the current version?

The update completes successfully, but when it reboots, it gets to "loading VMWare Hypervisor" gets to the end, and just a blinking cursor. And it just sits there.

I have to reset the computer to get it to boot and in doing so it reverts back to 4.0U2

Something might be screwed up on partition 0 or the bootbank that 4.1 get's installed to. I would probably try a repair install and then upgrade again. After you boot back to 4.0 what do you see in /altbootbank? If you open boot.cfg in /altbootbank do all the files that it reference exist?

/altbootbank and the contents of boot.cfg look good to me

I do see ACPI=FALSE an uwSwap=FALSE for the kernelopts. Not sure if that is right or not (would have to check to see what my BIOS settings are).

How do I do a repair install?

Page 43 - http://www.vmware.com/pdf/vsphere4/r40/ ... _guide.pdf

OK i can try that, although it does sound a little scary.

I assume I need to save my config (since it looks like that gets wiped out).

I hope that is the only thing I really need to do...

Or should I also backup my Disk0 (I have ESX installed on it, and the remaining disk I use for storage).

If you've done a lot of configuration of ESXi you'll want a system configuration backup. The repair install should preserve the VMFS datastore on the install drive, but a backup of VMs is always a good idea regardless.

Interesting. I don't seem to be able to find ESXI 4.0 Update 2 on the vmware site.

Well, I guess I do, but it says that I am not authorized to download it. How do I get a serial number for it?

I can get 4.0 U1, but my host is actually running 4.0 U2

You can try signing up for an eval of vSphere and then on the download page there is a previous versions link.