I hope this time most of the VMware administrators  will be busy with upgrading their infrastructure to vSphere 6. There are some rare situations in which your ESXi upgrade to 6.0 may fail due to some old firmware or drivers or may be whatever reasons. Most of the administrators will be aware  about rolling back vCenter or VM upgrade by reverting it to previous snapshot. Most of them may be unaware about the rolling back your ESXi upgrade. This post explains you the procedure to roll back your ESXi 6.0 upgrade to previous version i.e ESXi 5.5.

Procedure to Downgrade or Rollback your ESXi 6.0 Upgrade:

After the ESXi upgrade is failed or Hung, reboot your ESXi host. Durig ESXi host boot up, hit  Shift+R

Recovery mode will display the ESXi build version which you were upgrading from. If you want to roll back to the previous version, hit Y to go back to the previous version of ESXi. In my case , I was upgrading my ESXi host from ESXI 5.5 to ESXi 6.0. So I am hitting Y to rollback to previous version ie. ESXi 5.5.

Thats it. Your ESXi server will boot with the previous version of the ESXi i.e ESXi 5.5. This is a permanent and you will not able to boot to ESXi 6.0 until your next successful upgrade. I hope this is informative for you. Thanks for Reading!!!.  Be Social and share it in social media, if you feel worth sharing it.