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Archive for December, 2015


VMware Esxi – Mounted ISO won’t boot “Operating System not Found” (Everything is set correctly)

I recently had an issue with a VM on Esxi 5.5 that seemed to have the MBR (master boot record) messed up.  For whatever reason when it was rebooted it kept saying “Operating System Not Found”.  What I wanted to do is to boot the VM with an ISO image of the operating system and get to the command prompt to use DiskPart to make the correct partition active.  None-the-less I shut down the VM went to edit settings and pointed the CDROM to an ISO on the datastore.  In this particular case the datastore was local storage.  I checked the Connect at Power On and Connected boxes at the top of that window and then went to the next tab and set the boot options to force the VM into the Bios on the next boot.  I then booted into the bios and confirmed that the CDROM was at the top of the boot order and not below the hard drive.  Saved and Exited the bios.  At that point I assumed I’d be on my way.

Guess what?  This post wouldn’t be here if that was the case.  What followed was a boatload of reading posts from people that didn’t know how to properly mount an iso and  people explaining how to properly do it.  Every few posts I’d see someone saying, I know how to do all that and it’s all right but it’s still not working.  I could relate to them, because that was my case.  Nothing I did could get this thing to boot to that ISO.  I tried all kinds of stuff.  At the end of the day I didn’t want to rebuild this VM because there was a bunch of stuff on there that I really didn’t want to have to re-setup.  So the hunt was on.  Unfortunately the company I was working with didn’t have tech support from VMware….bummer.  I tried mounting the ISO to a new VM and whala it booted right up.  Tried to compare all the settings on the vm, tried to clone my vm, tried to upgrade my vm, tried cussing at my vm…none of it worked.

Ultimately I was in the bios of the VM for the millionth time and I noticed that the Primary Master didn’t have anything listed on the first page.  For whatever reason I remembered back to when you had to set the IDE to what kind of device was on it.  I figured at this point I’d try anything.  I set it to CDROM.  Saved and Exited.  It booted right into the ISO!!!

I can say I have never had to do this before in all of my experience with VMware.  Who knows if it’s some sort of bug, or just crappy luck.  Either way I hope this helps someone else from not having to go through what I did.

If you need to know how to do the DiskPart here is what I did:


  1. Boot to the ISO of the OS select recovery then run the Command Prompt

  2. Start DISKPART by running the following command: diskpart

  3. DISKPART will start and you will be at the “DISKPART>” prompt.

  4. List the drives by running the following command: list disk

  5. The installed drives will be listed, starting with Disk 0. In most cases, Disk 0 is the booting drive and also the drive containing the booting partition. You need to select the drive that contains the partition which needs to be set active. In this example, that is Disk 0.  I removed any other drives from my VM before this just so I didn’t accidentally choose the wrong one. Select the appropriate drive by running the following command: select disk 0

  6. The next step is to select the partition. To see the list of partitions on the drive, run the following command: list partition

  7. Select the partition which needs to be set active. In this example, Partition 1 is the desired partition.  In Windows Server 2008 R2 you want to select the small partition that is around 100mb.  select partition 1

  8. Set the selected partition active by running the following command: active

  9. Finally, exit DISKPART: exit