You may sometimes need to revert the ESXi back to a previous, stable state in case that the installed patches have caused problems and instability.
It’s very simple, just follow these steps:
1- connect to the host direct console either vial direct KVM, or remote KVM.
2- reboot the server with the method that suits you.
3- once you see the boot screen of ESXi appears, this one below, press Shift + R keys once. the letter “R” here stands for “Roll-back”.
4- as you can see below, the version and build number that is currently active, and the previous image available to be restored is displayed. You could recover to a one state back only. So, this is a bit like a snapshot for ESXi itself. This is pretty handy.
5 – press “Y” to accept reverting back to the previous state.